UF/IFAS Citrus Magazine - December 2025

December 2025 Vol. 1, Issue 2

UF/IFAS

Citrus Magazine

Time to plan for the spring

UF/IFAS Citrus Magazine

Welcome

Chris Oswalt: A Legacy of Knowledge, Leadership, and Friendship in Florida Citrus As we approach the end of December, the UF/IFAS citrus community prepares to say goodbye to a colleague who has faithfully served and greatly benefited numerous growers, researchers, and his fellow Extension agents. Chris Oswalt, the multi-county citrus agent for Polk and Hillsborough Counties, will be retiring after decades of dedicated service.

Chris’s journey in citrus Extension began decades ago, inspired by his family’s involvement in the industry. Yet, his path was never linear. From early work on the Florida Department of Citrus’s mechanical harvesting project, to a stint with an agri-chemical Credit: Tonya Weeks, UF/IFAS company in the late 1970s, Chris eventually found his calling in citrus production and Extension work. He earned both his bachelor’s and master’s degree at UF and accumulated a lifetime of experience that he has generously shared with Florida growers throughout his career.

Those of us who have worked alongside Chris know that he is the embodiment of practical wisdom. Growers know him as a go-to resource, someone whose advice is always grounded in reality, and keenly aware of the challenges growers face in their grove operations. Researchers and fellow Extension specialists have long relied on his guidance to translate scientific research into practical, workable strategies. Chris has always exhibited an uncanny ability to grasp the intersection of science with the art of production, a skill he honed through years of hands-on experience and careful observation.

Throughout his career, Chris has played a key role in shaping Florida’s citrus Extension programs. He has been a leader among UF/IFAS citrus agents, mentoring new colleagues and preparing the next generation of Extension professionals. His contributions to events like the Florida Citrus Growers’ Institute in Avon Park have brought growers, researchers, and industry partners together year after year fostering collaboration, sharing critical knowledge, and strengthening the Florida citrus industry as a whole.

Those of us who have benefited from Chris’s guidance know that his legacy extends far beyond technical knowledge. He has been a friend to many and is respected by all. He has a generosity of spirit that makes him approachable, whether mentoring colleagues, advising growers, or collaborating with researchers.

Looking back, it is clear that Chris will retire having left an indelible mark on Florida citrus.

Chris, as you welcome a well- earned retirement, please know that the UF/ IFAS citrus community will continue to benefit from the foundation you have built, the wisdom you have shared, and the friendships you have forged. Thank you for your years of service, your leadership, and your dedication to the Florida citrus industry and UF/IFAS Citrus Extension programs!

Sincerely, Michael E. Rogers UF/IFAS Statewide Citrus Research and Extension Coordinator

In Season: What To Do Now! During this period, citrus trees transition through a wide range of growth stages, from a low metabolic state in January to active growth, blooming, and fruiting in spring. The primary goal of grove management is to provide trees with the resources needed to remain dormant during the coldest months and then support their transition into active growth as the freeze window passes.

Pest and disease management also become a critical aspect of spring grove care. As trees flush, they become more susceptible to insect pressure and disease outbreaks. Many foliar diseases, although not always visible until summer, begin to establish in the spring, making early monitoring and intervention essential.

Horticultural Management • Monitor and prepare for potential freezes • Plan prebloom and postbloom fertilization • Irrigate regularly and frequently in March and April • Apply cytokinin-rich plant growth regulators (PGRs) to promote growth

Disease Management • Monitor weather for postbloom fruit drop (PFD) conducive conditions, apply fungicides if needed • Apply fungicides for Alternaria brown spot and citrus scab, if needed, for tangerines and tangerine hybrids • Apply copper to prevent early-season infection of canker and melanose

Credit: UF/IFAS

Pest Management • Dormant sprays for psyllids before bud break occurs • Apply a bee safe systemic chemistry prior to fruit set

4

UF/IFAS Citrus Magazine December 2025

In this issue....

READ. APPLY. GROW. Page 6 Horticultural Grove Management Page 8 When is the best time to perform oxytetracycline trunk injections?

Page 10 Citrus Nutrition Considerations for Year-Round Nutrient Management Page 13 Citrus Insect and Snail Management Page 16 Disease Management

RESEARCH:

Editorial Committee

WHAT’S NEXT

Ute Albrecht

Page 25 Will a lower price bring back orange juice demand?

Megan Dewdney

Michelle Danyluk

Page 26 A New Chapter for Citrus: Turning Orange Peels into Heart-Healthy Gold Page 29 Somatic Cybridization in Citrus: A New Frontier for Disease-Resistant Cultivars

Lauren Diepenbrock Mark Ritenour Michael Rogers Muhammad Adnan Shahid Ariel Singerman Matt Smith Tripti Vashisth Editorial Jamie Burrow Graphic Designer Tonya Weeks

Page 32 Genetic Transformation Offers Hope Against Huanglongbing Page 34 Helping Florida Citrus Growers Through Mighty Collaboration Page 38 Early Performance of New Citrus Rootstock Cultivars

UF/IFAS Citrus Research https://citrusresearch.ifas.ufl.edu

Contact us at citrusresearch@ifas.ufl.edu

Credit: Tonya Weeks, UF/IFAS

Cover Credit: Tonya Weeks, UF/IFAS

UF/IFAS Citrus Magazine December 2025

5

Horticulture - Read. Apply. Grow.

Horticultural Grove Management Alissa Hevesh and Tripti Vashisth From January through early February, citrus trees have relatively low water and nutrient demands. As temperatures rise and spring approaches, these demands increase as trees resume growth, bloom, set fruit, and develop new leaves. The main goal of horticultural management during this period is to promote fruit set and spring vegetative growth. Fruit that develops with a healthy canopy and abundant leaves nearby is more likely to grow to maturity and reach harvestable size.

Irrigation Adequate irrigation is essential for optimal tree growth, fruit development, and yield. In Florida, January through early February is typically cooler, and trees require less water. However, as weather warms and trees enter periods of active growth, water availability becomes critical.

Spring is often a dry season in Florida, coinciding with intense physiological activity (flowering, fruit set, and vegetative growth) all of which require abundant water. For HLB-affected trees, irrigation management is even more important. These trees have smaller and weaker root systems, which limits their ability to take up sufficient water and nutrients. Although HLBaffected roots remain efficient at uptake, the reduced root mass means they cannot meet canopy demand.

The severity of HLB symptoms correlates with the extent of root loss and water deficit. Because of these challenges, precise irrigation scheduling is critical and should be adjusted according to grove conditions.

A recent field trial demonstrated that trees receiving frequent irrigation produced more than twice the yield of trees on conventional, everyother-day irrigation schedules. Both treatments received the same total volume of water, but the frequency differed. The trees receiving frequent irrigation developed larger, denser canopies (83% vs.

75% light interception).

These findings emphasize that consistent and frequent watering during spring and early summer,

Fertilization Citrus trees have their highest nutrient demand from late winter through summer, when flowers, fruitlets, and new shoots are actively growing and competing for resources. As fruit growth slows later in the season, nutrient requirements decrease.

The first fertilizer application should be made from early February through the start of flowering to prepare trees for new growth. Fertilizer applications made earlier (December—January) are often ineffective, as cold soil temperatures limit root uptake. Winter applications also carry a higher risk of leaching, especially when micro-sprinkler irrigation is used for freeze protection.

Late-winter fertilization can also increase freeze susceptibility by encouraging tender new growth and can complicate psyllid management, as it overlaps with the overwintering ACP population.

During spring, citrus trees require high nitrogen availability to support vegetative growth, flowering, and fruit set.

• Apply up to 50% of the annual nitrogen rate between late winter and early summer.

• Apply an additional 25–30% before the onset of summer rains.

• As fruit develops, increase potassium applications.

Citrus fruit and blossoms Credit: Tonya Weeks, UF/IFAS

6

when rainfall is limited, is vital to support fruit development, improve retention, and maximize yield.

Regularly irrigated trees grow more vigorously and produce significantly higher yields.

UF/IFAS Citrus Magazine December 2025

• The annual N:K ratio should be 1:1.25 approximately.

Nutrients should be applied frequently in small amounts, rather than in large and infrequent doses.

HLB-affected trees particularly benefit from a steady supply of nutrients throughout the growing season.

Ideally, make 2—3 dry fertilizer applications during this period.

Growers in central and southwest Florida, where HLB is widespread, should avoid bloom-promoting nutritional sprays. Research shows that increasing flower number does not necessarily improve yield in HLB-affected trees, as heavy flowering often leads to poor fruit set and increased fruit drop. Excess flowering can also divert energy away from vegetative growth.

Foliar nutritional sprays can be effective for supplying micronutrients, especially where soil pH limits availability. For best absorption, apply foliar sprays to young leaves when they are two-thirds to nearly fully expanded, prior to hardening. However, foliar sprays should supplement, not replace, soil fertilization, as soil-applied nutrients ensure more uniform distribution throughout the tree.

Oxytetracycline (OTC) Trunk Injections Trunk injections of oxytetracycline (OTC) may begin as early as March and continue depending on variety and season: • Early-season and grapefruit varieties: March through May • Mid-season varieties: March through June • Late-season varieties: March through July

Congratulations

For detailed nutrient management recommendations, consult Nutrition of Florida Citrus Trees, published by UF/IFAS. Following these guidelines will help maintain healthy, productive trees and improve fruit yield.

Plant Growth Regulators (PGRs) The use of plant growth regulators (PGRs) during this period should focus on promoting vegetative growth and improving fruit development. While gibberellic acid (GA) can enhance vegetative growth, its use in the spring is not recommended. Applying GA at this time can stimulate excessive fruit set in HLB-affected trees, leading to heavy fruit drop later in the year.

Instead, cytokinin-based products, including some seaweed extracts, have shown positive effects on canopy growth and fruit development in HLB-affected trees when applied during spring and early summer.

However, not all seaweed extracts have the same activity, growers should review product formulations and field data carefully before use.

Recent field studies have also shown that brassinosteroids can promote growth in young citrus trees when applied during spring and summer, suggesting a potential role in recovery and canopy expansion.

Early Career Excellence Award 2025

Manjul Dutt

Assistant Professor, Horticultural Sciences UF/IFAS Citrus Research and Education Center American Society for Horticultural Science

Plant Biotechnology Professional Interest Group

UF/IFAS Citrus Magazine December 2025

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Horticulture - Read. Apply. Grow.

When is the best time to perform oxytetracycline trunk injections?

Ute Albrecht The timing of oxytetracycline (OTC) trunk injections can influence fruit size, juice quality, and OTC residue levels in harvested fruit. These effects are closely tied to the stages of citrus fruit development. Understanding when these stages occur helps growers choose the most effective injection period based on their management goals.

Stages of Fruit Development

Stage III–Fruit Maturation: During this final stage, fruits undergo non-climacteric ripening. Peel color changes, titratable acidity (TA) decreases, and sugar levels, measured as total soluble solids (TSS or °Brix), increase.

The timing and duration of each stage vary slightly by cultivar and environmental conditions, but the general pattern is consistent across citrus types.

Citrus fruit development occurs in three overlapping stages (Figure 1):

Effects of Injection Timing

Stage I–Cell Division: This stage lasts from the main flowering period until the end of physiological fruitlet abscission (commonly called June drop). During this time, cell division predominates, fruit growth is moderate, and peel thickness is greatest.

Stage I (March–June): OTC injections during this period (Figure 2) promote cell division, often resulting in larger fruit. The earlier the application, the greater the increase in fruit size. However, these larger fruits may take longer to mature; if harvested early, they may remain green with lower °Brix levels. On the positive side, OTC residues in the fruit are typically very low because the antibiotic is diluted as the fruit expands and because there is a longer period for degradation before harvest. Injections made in May or June can still improve juice quality while improving fruit size.

Stage II–Cell Enlargement: Beginning after June drop and lasting until just before color change, this stage is characterized by rapid enlargement of juice sacs within the segments. The peel gradually thins as fruit size approaches its final diameter.

Figure 1. Development stages of citrus fruit and effects of injection timing on fruit quality and OTC residues. Credit: Ute Albrecht, UF/IFAS

8

UF/IFAS Citrus Magazine December 2025

Stage II (July–September): Injections during this stage have less impact on fruit size (Figure 2) but can enhance soluble solids content, leading to higher °Brix readings and improved flavor.

Later injections within this period also tend to improve peel color. However, because fruit growth slows or stops toward the end of Stage II, OTC can no longer be diluted within the expanding fruit. As a result, residue levels can be expected to be higher with late injections.

Figure 2. Effects of oxytetracycline (OTC) injection month on citrus fruit quality.

• Injections made in September have Credit: Ute Albrecht, UF/IFAS been shown to cause OTC residues that exceed the legal limit of 10 parts per billion (ppb), even at lower °Brix development while keeping residues within application rates and with a 180-day pre-harvest acceptable limits. interval.

Yield Effects • August injections may also result in excessive While injection timing clearly affects fruit quality residues, particularly at higher rates. attributes and OTC residue levels, current research To balance improved juice quality with lower OTC indicates that the month of injection does not residues, growers are advised to complete OTC significantly influence total yield. injections by July. This timing allows for enhanced

Scan QR code for more information on all upcoming UF/IFAS events.

Save the Date

Statewide Citrus Grower Workshop January 14, 2026

CREC Grower Seminar February 10, 2026

UF/IFAS Southwest Florida Research and Education Center

UF/IFAS Citrus Research and Education Center

Join us for presentations and demonstrations focused on tools for today.

Citrus Field Day January 28, 2026 UF/IFAS Citrus Research and Education Center Join us for a follow-up field day to view OLL budlines on multiple rootstocks before harvest.

Get the latest citrus management strategies for spring.

Florida Citrus Growers’ Institute April 14, 2026 South Florida State College Learn about effective management of HLB and other challenging pests affecting the industry.

Visit the Statewide Citrus Calendar for registration links and additional program information. https://go.ufl.edu/citruscalendar

Horticulture - Read. Apply. Grow.

Citrus Nutrition Considerations for Year-Round Nutrient Management Davie Kadyampakeni, Kelly Morgan, and Tripti Vashisth Timing of Fertilizer Applications In Florida, citrus trees should always be fertilized using split applications. Different nutrients are needed at different times of the year to support vegetative growth, yield, fruit quality, and compliance with best management practices (BMP). These goals cannot be achieved with a single annual application, especially on Florida’s sandy soils, which have limited nutrient- holding capacity.

The active growing season for citrus trees in central and southwest Florida typically spans about nine months (February–October). Citrus trees have peak nutrient demand in late winter (February–March) and spring (May–June), followed by moderate to low demand in summer, fall, and winter. The rainy summer months bring the greatest risk of nutrient leaching, which further reinforces the importance of split applications. Splitting fertilizer also reduces the risk of major nutrient loss from a single misapplication or natural event such as a hurricane.

Peak nutrient demand in bearing trees occurs between bloom and the end of fruit growth Stage I (cell division). Because bloom timing varies by variety and year, the trees should be “primed” before bloom with a fertilizer application in late winter (around February).

This prebloom feeding supports new flush and early fruit set.

Fertilization

should

end

by

October.

Late

fall

applications can interfere with fruit color development and sugar accumulation (°Brix), especially in fresh fruit destined for the early market. Excess nitrogen during this period delays color break and reduces pack-out.

Waiting to harvest until fruit color and sugar improve can also increase the risk of preharvest fruit drop in HLB-affected groves. Late fertilizer applications can further complicate psyllid management and increase freeze susceptibility. Nutrients applied in winter are also likely to leach before tree uptake.

Splitting Fertilizer Applications Dry soluble fertilizers are often applied in three to four equal splits for convenience (e.g., 33.3% or 25% per application). More frequent splits are possible but may not be practical due to equipment calibration limitations or cost.

Fertigation, however, offers greater flexibility. Liquid fertilizers can be applied weekly, biweekly, or monthly, allowing growers to more precisely match tree nutrient demand.

Figure 1A shows the incorrect method for applying three splits of fertilizer in a linear fashion using equal time increments, which mismatches with the peak nonlinear demand for nutrients by citrus in the spring.

In this situation (Figure 1A), the trees would likely encounter nutrient deficits during April. A better approach (Figure 1B) is to front-load applications, applying two of the three adjusted fertilizer doses

Figure 1. Linear trend of nitrogen supplied by three equal allocations (33.3%) of fertilizer and equal time increments during the growing season (A; not recommended) versus nonlinear supply of nitrogen from three unequally timed 33.3% increments (B) and four unequally timed 25% increments (C). Approximate nitrogen requirements for citrus by calendar month are depicted as increasing green color and Low (L), Moderate (M), and High (H) labels. Credit: Morgan et al. 2025.

10 UF/IFAS Citrus Magazine December 2025

between bloom and the end of Stage I growth. A similar strategy for four unequal splits is shown in Figure 1C. Growers may need to experiment with timing to find the best schedule for their varieties and harvest windows.

For early-season varieties, the final nitrogen application should occur in mid-summer, while mid- and lateseason varieties can receive their last split in late summer or early fall. Keep in mind that fertilizer applied during the rainy season carries a higher leaching risk.

For fresh-fruit production, leaf sampling can help maintain nitrogen in the proper range (Table 1): • High end of the optimum range (≈2.7%) during bloom, fruit set, cell division and cell enlargement stage • Low end of the optimum range (≈2.5%) or the low range (2.2–2.4%) during fruit maturation in the fall and winter The optimal timing for potassium differs slightly from nitrogen. Citrus requires less K during bloom and fruit set, but more K than N during the cell division, enlargement, and maturation stages. Potassium is especially important for proper fruit sizing.

Example N:P₂O₅:K₂O fertilizer blends for different growth stages include: 1. 15:3:11–prebloom stage 2. 9:3:18–during cell division stage 3. 12.5:3:18–during cell enlargement stage HLB and Micronutrient Requirements Huanglongbing (HLB) causes leaf chlorosis and blotchy mottling similar to Mn and deficiencies. The disease also damages feeder roots, the main site of nutrient uptake, leading to deficiencies of K, P, Mg, Ca, Mn, Zn, and Fe. Research shows that supplemental foliar and soil applications of Ca, Mg, Mn, and Zn can help mitigate HLB symptoms. This has led to the widespread adoption of enhanced foliar nutrition programs across Florida.

However, the effectiveness of these programs can vary by grove tree health and nutrient formulation.

Because no single program fits all situations, UF/IFAS recommends at least two leaf tissue analyses per year to accurately assess nutrient status and adjust fertilizer applications accordingly.

Element

Unit of Measure

Deficient

Low

Optimum

High

Excess

N

%

< 2.2

2.2–2.4

2.5–2.7

2.8–3.0

> 3.0

P

%

< 0.09

0.09–0.11

0.12–0.16

0.17–0.30

> 0.30

K

%

< 0.7

0.7–1.1

1.2–1.7

1.8–2.4

> 2.4

Ca

%

< 1.5

1.5–2.9

3.0–4.9

5.0–7.0

> 7.0

Mg

%

< 0.20

0.20–0.29

0.30–0.49

0.50–0.70

> 0.70

Cl

%

---

---

< 0.2

0.20–0.70

> 0.701

Na

%

---

---

---

0.15–0.25

> 0.25

Mn

mg/kg or ppm2

< 18

18–24

25–100

101–300

> 300

Zn

mg/kg or ppm

< 18

18–24

25–100

101–300

> 300

Cu

mg/kg or ppm

<3

3–4

5–16

17–20

> 20

Fe

mg/kg or ppm

< 35

35–59

60–120

121–200

> 200

B

mg/kg or ppm

< 20

20–35

36–100

101–200

> 200

Mo

mg/kg or ppm

< 0.05

0.06–0.09

0.10–2.0

2.0–5.0

> 5.0

1

Leaf burn and defoliation can occur at Cl concentration >1.0%. : 2 ppm = parts per million.

Table 1. Guidelines for interpretation of leaf analysis based on 4-to-6-month-old spring-flush leaves from nonfruiting twigs of healthy trees.

Source: Florida Citrus Nutrition Guide

UF/IFAS Citrus Magazine December 2025 11

Horticulture - Read. Apply. Grow.

Enhanced nutrition programs alone cannot restore pre-HLB production levels, but maintaining adequate leaf nutrient concentrations improves canopy volume and yield stability. Current UF/IFAS guidance (Table 2) recommends three foliar applications per year, following spring, summer, and fall flushes (March, May, and September), to maintain nutrient concentrations within the optimal range.

Method

Timing

Mn

Zn

Cu

B

Fe

Foliar

Yes

Yes

Yes

Yes

No

Soil

Yes1

No

Yes

Yes

Yes

Foliar

When spring flush leaves reach full expansion

Soil

Any time as needed

Rates (applied in a combination of foliar and soil applications)

For example, previous UF/IFAS recommendations for Mn and Zn were 5 lb metallic per acre per year. These rates were tripled in 2022 for HLB-affected trees, now totaling 15 lb metallic per acre per year applied in three foliar sprays.

Table 2. Recommended methods, timing, and rates for micronutrient application to citrus groves.

Source: Florida Citrus Production Guide

Pound (lb) metallic equivalent/acre Foliar

15

15

Soil

20

25

5

1

See below2

1

Soil applications of Mn are not recommended on calcareous soils.

2

Acid soil: Fe-EDTA, 20 grams/tree; Calcareous soil: Fe-EDDHA, 50 grams/tree.

Nutrient Management Key Points • Split fertilizer applications are essential for Florida citrus because of the state’s sandy soils and long growing season. Apply nutrients in multiple smaller doses from February—October to match tree demand and reduce leaching losses.

• Peak nutrient demand occurs between bloom and the end of fruit growth Stage I (cell division).

Apply two-thirds of total nitrogen and potassium during this period to support flush and early fruit development.

• Avoid fertilization after October. Late-season nitrogen can delay color break, reduce Brix, increase fruit drop, and elevate freeze risk.

• Tailor fertilizer timing to variety and harvest season: finish nitrogen applications by midsummer for early varieties and late summer to early fall for mid- and late-season fruit.

• Leaf sampling at least twice per year is essential to monitor nutrient status and adjust fertilizer programs for grove-specific conditions.

12 UF/IFAS Citrus Magazine December 2025

• Potassium demand exceeds nitrogen during enlargement and maturation, especially important for achieving optimal fruit size in fresh-fruit groves.

• HLB-affected trees have higher micronutrient requirements due to root loss and reduced uptake.

Foliar or soil applications of Ca, Mg, Mn, and Zn can help sustain canopy health and yield.

• UF/IFAS now recommends three foliar micronutrient applications annually (March, May, and September) for HLB-affected trees—tripling Mn and Zn rates from 5 lb to 15 lb metallic per acre per year.

• No single fertilizer program fits all groves; customization based on leaf analysis and field observations remains key to maintaining productivity under HLB pressure.

Entomology - Read. Apply. Grow.

Citrus Insect and Snail Management Lauren Diepenbrock From January through February, most citrus pests remain relatively inactive as cooler temperatures fall below their optimal range. However, occasional warm days can trigger short periods of pest activity.

In recent years, localized infestations of lebbeck mealybug have been observed on early set fruit, and Bulimulus snails have shown notable activity during warm spells.

As we move from bloom into early fruit development, many of our common citrus pests become active and remain so through the rest of the growing season. The following summary outlines key pests, their seasonal behavior, and management needs for this period. Always refer to the latest UF/IFAS Florida Citrus Production Guide for current pesticide recommendations.

Asian Citrus Psyllid (ACP)

Bulimulus Snail

Dormant sprays applied before budbreak are strongly recommended to reduce adult ACP populations heading into spring. Suppressing adult psyllids early helps minimize egg-laying on new flush, lowering the initial population and reducing overall pressure during the season.

Bulimulus spp. snails do not truly hibernate, though their activity is reduced in cool months and often goes unnoticed. On warmer days, they become active and feed within the grove, retreating to sheltered areas as temperatures drop at night.

The rationale and benefits of dormant sprays were discussed in Citrus Industry Magazine (January 2022).

In short, this timing takes advantage of the reduced number of adult psyllids in groves during the winter.

By further reducing this population, we move into the spring flush with fewer ACP ready to immediately infest and start the next generation. This can reduce the overall ACP pressure in groves. Psyllid numbers increase rapidly during the spring flush, when adults lay eggs on feather flush. Once hatched, the nymphs have limited mobility and are highly susceptible to control measures, making timing applications around major flush periods an effective strategy for managing local ACP populations.

While the exact overwintering behavior of this species is not fully understood, it is likely that they burrow into the Citrus leafminer larvae and “mining” damage on underside of young leaf.

Credit: Lauren Diepenbrock, UF/IFAS

Citrus Leafminer (CLM) Like ACP, citrus leafminer adults are attracted to new flush for egg-laying. Insecticides applied during flush can limit CLM damage to tender leaves while also helping suppress ACP activity.

CLM control is particularly important for young tree development, as heavy leafminer feeding reduces photosynthetic area and limits energy available for growth. In addition, reducing local CLM populations will also help minimize canker infection following storm or wind events.

Mixed sizes of Bulimulus bonariensis snails on fruit, March 2023.

Credit: Lauren Diepenbrock, UF/IFAS

UF/IFAS Citrus Magazine December 2025 13

Entomology - Read. Apply. Grow. soil to insulate themselves from cold. Populations typically reappear in March, and management actions taken at that time may help reduce their impact later in the season. Research is ongoing to develop effective management recommendations for this pest.

Lebbeck Mealybug Lebbeck mealybug populations tend to increase around fruit set (March–April). Applying systemic insecticides prior to fruit set can help reduce the number of reproductive females and protect developing fruit from damage.

Because bloom is often still present during this period, always verify label restrictions and use only bee-safe insecticides when applying treatments for this application.

Lebbeck mealybug infestation on young fruit.

Credit: Lauren Diepenbrock, UF/IFAS

Summary Early-season pest management, especially before and during flush, can significantly influence pest pressure throughout the year. Monitoring grove conditions closely, applying treatments at optimal timings, and following label and pollinator safety guidelines are key to maintaining healthy trees and fruit set.

Lebbeck mealybug on flower bud.

Credit: Lauren Diepenbrock, UF/IFAS

Congratulations Dr. L.W. ‘Pete’ Timmer Professor Emeritus, Plant Pathology UF/IFAS Citrus Research and Education Center

Florida Citrus Hall of Fame Inductee Class of 2026 14 UF/IFAS Citrus Magazine December 2025

Weeds Highlight : Parthenium weed (Parthenium hysterophorus) Ramdas Kanissery Parthenium weed, also known as Ragweed Parthenium, White Top Weed, Santa Maria Feverfew, or False Ragweed, is a fast-spreading annual weed in the sunflower family (Asteraceae). Native to Central and South America, it has now become common across many tropical and subtropical regions. In Florida, it often appears along citrus grove edges, roadsides, and disturbed areas, but can quickly move into tree rows if left unmanaged, competing with citrus trees for resources.

This upright, branching plant usually grows between one and five feet tall (Figure 1A). The gray-green leaves are deeply lobed (Figure 1B), covered with fine hairs, and give off a strong odor when crushed. Small white flower clusters form at the tips of the branches (Figure 1C), each producing many tiny black seeds that can survive in the soil for several years. While it may look similar to common ragweed or dogfennel, its bright white blooms and distinct scent make it easy to recognize.

Fun Facts: A single Parthenium plant can produce more than 25,000 tiny seeds that remain viable in the soil for several years. This makes early detection and control very important to keep the weed from spreading into new areas. Although Parthenium weed belongs to the sunflower family, it is known to cause problems rather than benefits. Its pollen and tiny plant hairs can trigger skin irritation and allergies in people and livestock, which is why it is sometimes referred to as the “allergy weed.”

Management Tips • Scout early: Keep an eye on grove edges, ditches, and roadways, especially after rain when seedlings (Figure 1D) are likely to appear.

• Prevention: Clean mowers, sprayers, and other equipment after working in infested areas to avoid spreading seeds into groves.

Chemical Control • Pre-emergence: Herbicide products containing simazine, diuron, flumioxazin or indaziflam can help prevent seed germination of parthenium weed.

• Post-emergence: Herbicide products containing glufosinate ammonium, saflufenacil, or 2,4-D work well on young, actively growing Parthenium weed.

In some areas of Florida, this weed has shown tolerance to common herbicides like glyphosate.

To maintain good control, rotate herbicides with different modes of action. Always read and follow herbicide product label directions carefully to achieve effective weed control and to protect citrus trees from injury.

Act early because once Parthenium weed becomes established, it spreads quickly. Regular scouting, timely herbicide use, and good sanitation are the best ways to keep this aggressive weed out of citrus groves.

Figure 1. Parthenium weed in a citrus grove (A), close view of leaves (B), flower clusters (C), and seedling stage (D).

Credit: Ramdas Kanissery, UF/IFAS

Pathology - Read. Apply. Grow.

Disease Management Megan Dewdney While I do not have a crystal ball to predict the weather in the spring of 2026, current forecasts indicate a neutral weather pattern. This means temperatures and rainfall should remain within the average range for Florida following a late fall and winter of warmer temperatures and lower rainfall. While it is difficult to predict how severe foliar diseases will be in 2026, it is important to evaluate your risk from these diseases that erode profit margins. Each grower has a different level of acceptable risk based on fruit destination and other economic factors, but foliar diseases can suddenly flare up in ways that cannot be ignored. When that happens, it is often too late for the current season.

As a side note, phytophthora root rot programs should begin with the spring root flush right after bloom, if the number of propagules is above the threshold of 10–20 propagules/cm³.

Citrus Canker Plan to conduct at least minimal canker suppression even if fruit are destined for juice. In this case, target early-season lesions to maximize fruit retention. Early lesions become large and can cause up to 80% of fruit to drop prematurely, especially if located near the stem. After multiple seasons with hurricanes, many groves have stem cankers that can exude inoculum for nearly four years. These bacteria are ready to infect once the weather warms and susceptible leaves and fruit are present. All they need is water!

To protect against early-season infection, initiate a spray program when fruit reach more than ¼ inch in diameter for oranges or ½ inch for grapefruit (typically mid- to late March). Apply at least two applications of a good-quality copper product (FRAC M 01) no more than three weeks apart. If no further applications are made, fruit may still develop canker lesions, but they will be smaller and cause much less drop.

Keep in mind that fruit are most vulnerable at ¼–1¼ inch diameter for oranges and ½–1½ inch for grapefruit, particularly for fresh fruit. Grapefruit are always highly susceptible and will require greater effort to keep canker levels to a minimum.

Young Plantings Young trees are particularly susceptible to canker. They produce new flush frequently, and a large proportion of stems are vulnerable. Infected stems are likely to become scaffold limbs and are undesirable to remove once lesions develop. Copper cannot protect rapidly

16 UF/IFAS Citrus Magazine December 2025

Citrus canker Credit: Tonya Weeks, UF/IFAS

growing leaves or those damaged by leafminer. A better option for young trees is plant defense inducers such as Actigard® FRAC P 01) or Aura Citrus® (FRAC P 09), which are effective against stem lesions and help minimize foliage infections.

If trees are within individual protective covers (IPCs), canker is less of an issue because the netting reduces wind speed and droplet size. However, as trees grow into their covers and touch the netting, canker risk increases. See application and rate details in the Florida Citrus Production Guide (https://edis.ifas. ufl.edu/publication/CG040).

CUPS Structures Canker outbreaks can occur in CUPS structures and should be managed early to prevent spread.

Fortunately, the disease can be controlled relatively easily. Inside CUPS, lower wind speeds limit bacterial spread, but routine operations such as equipment movement or spraying can move inoculum without a suppressive material in the mix.

For early infections, trim affected portions of trees and treat the tree plus up to five surrounding trees in each direction. SAR inducers may also be good options within CUPS. Because of phytotoxicity concerns in high temperatures (>94 °F) and increased mite populations, apply copper early in the morning when risk is lowest.

Keeping canker restricted to small areas is key.

Lowering the quality of fruit from 25 trees is preferable to compromising an entire block.

Postbloom Fruit Drop (PFD) Even in dry springs, PFD is reported annually in groves that remain wet or foggy. Although 2026 is expected to be relatively dry in the beginning, scout these blocks carefully. ‘Valencia’ and ‘Navel’ oranges are the most susceptible, while grapefruit are the least, though all cultivars can be affected.

PFD is primarily a disease of flowers and there is no disease if there are no flowers. If rain occurs leading into full bloom, scout any blocks with a history of PFD. To optimize application timing, focus on your most profitable blocks and use the Citrus Advisory System (http://agroclimate.org/tools/cas/). The system uses FAWN data, but if your grove is wetter or foggier than the nearest FAWN site, consider applying when the disease risk index approaches 0.18–0.19 rather than waiting for 0.20.

Few fungicides are effective against PFD, and copper is ineffective. Strobilurin-containing fungicides (FRAC 11) remain among the most effective options but carry a high resistance risk. No resistance has been observed in Florida, but only four FRAC 11 applications are allowed per season. If one is used for PFD, only three remain for other diseases. Overuse increases the chance of selecting resistant isolates. Since few new fungicides are being registered, rotate modes of action and consult the Florida Citrus Production Guide for more details and options (https://edis.ifas.ufl.edu/ publication/CG007).

Greasy Spot Recently, greasy spot has resurged in young trees, with and without IPCs. Though it may seem minor, untreated greasy spot causes significant defoliation, limiting canopy and root development. The inoculum forms in decomposing leaf litter and is released when the litter is wetted, primarily in spring but often throughout the year.

The most vulnerable leaves to infection are the most recently matured leaves after the fungus has grown on the surface for several months. On mature trees, the most damaging infections occur on the spring flush by late August or early September. Young trees, which flush continuously, are vulnerable nearly year-round, though it’s impractical to treat continuously.

Focus on spring and summer applications.

Grapefruit are most susceptible, followed by early oranges; ‘Valencia’ and tangerines are less affected.

Apply treatments in late May or early June, followed by another in early July (~3 weeks later). If symptoms were severe or flush abundant, apply a third in early August.

Copper (≤2 lb/acre) remains the preferred treatment as it is effective and economical. Oil applications can also help with defoliation, especially on ‘Valencia’. Avoid applying copper or oil in hot weather (>94 °F) and do not mix with additives. Copper is also effective against other fungal diseases except PFD. Fresh Fruit On fresh grapefruit, greasy spot causes rind blotch, producing large black rind patches or degreening problems (“greasy green”). Grapefruit are especially susceptible because of their light rind color.

The first application should be in late May or early June, followed by another in early July. If rind blotch was severe the previous year, a third application in early August may help. While horticultural oil is sufficient for leaves, it’s generally ineffective for rind blotch.

Copper remains the most economical option, but if temperatures exceed 94 °F, consider Enable® (FRAC 3) or premixes such as Amistar Top® (FRAC 11+3) or Pristine® (FRAC 11+7). Limited data also suggest promise for Double Nickel™ (FRAC BM 02) and Miravis Top® (FRAC 7+3).

Avoid two consecutive non-copper applications and do not rely solely on FRAC 11 fungicides to prevent resistance.

CUPS Structures Greasy spot can also be problematic in CUPS because high humidity and poor air circulation promote fungal growth. Pruning to open canopies can help increase air flow. Studies show ascospore peaks in early May, similar to outdoor groves, but leaves may become UF/IFAS Citrus Magazine December 2025 17

Pathology - Read. Apply. Grow.

Citrus Disease Management Spray Timing Schedule Shaded areas represent suggested spray periods.

Refer to the annual Florida Citrus Production Guide for more details.

DISEASE

FRUIT MARKET JAN

Black spota

Greasy spotb

FEB

MAR

APR

MAY

Processed/fresh

Processed/fresh Processed

Cankerc

Processed/fresh

Melanosed

Fresh

Alternaria brown spote

Fresh

Citrus Scabf

Fresh

Postbloom fruit dropg

Processed/fresh

Phytophthora Processed/fresh root roth Phytophthora brown roti

Fresh

Agal spotj

Fresh

a. Optional application if there are high rainfall amounts in April, otherwise begin applications in early May b. Optional application in late July–early August if infection was severe and has caused defoliation in the previous year c. Canker is a bacterial disease managed with copper; apply every three weeks d. Apply copper every three weeks e. Frequency of sprays depends on amount of rainfall; start applications at ¼” to ½” full expansion with the second spray at petal fall; see Florida Citrus Production Guide for more details

18 UF/IFAS Citrus Magazine December 2025

THE LABEL IS THE LAW! KEY: Oranges

JUN

Grapefruit

‘Valencia’

Tangerines and hybrids

JUL

AUG

SEP

OCT

All varieties

Optional applications

NOV

DEC

f. Apply first application at ¼” flush; second application at petal fall; and third application three weeks after petal fall; application time will vary depending on year and location, but typically begins mid-February

g. Make applications only if there is sufficient bloom to warrant the application. Follow recommendations of Citrus Advisory System (agroclimate.org/tools/cas) for application timing

h. Apply when phytophthora threshold is above 20 propagules/cm2 of soil i. Usually only occurs in groves with phytophthora history j. Phosphite fungicide at 0.5 gal/acre is the best option currently

Credit: UF/IFAS

UF/IFAS Citrus Magazine December 2025 19

Pathology - Read. Apply. Grow. susceptible earlier due to warmer CUPS conditions.

If applications in previous years at the timing described above did not have the expected outcome, consider starting applications in mid-May to improve timing.

Blemishes are a major concern in the heat as is mite damage, so choose a fungicide carefully that can be used in hot weather when copper or oil is inadvisable.

As a reminder, efficacy of fungicides within the CUPS system is not known at this time.

Citrus Black Spot Citrus black spot continues to move north from southwestern Florida and was recently detected in Manatee, eastern Polk, DeSoto, and a small part of Highlands County. As fruit color changes this winter, scout late-season cultivars for unusual symptoms and contact your local CHRP office if you suspect infection.

Black spot rarely affects leaves. The wind- and waterdispersed spores develop in leaf litter, dead twigs, and ripening fruit. Fruit remain susceptible from petal fall to mid–late September. April is typically dry, so delay applications until early May unless April is unusually rainy.

Monthly fungicides applications are recommended but may be cost-prohibitive. Because fruit are most susceptible early, prioritize early-season sprays if reducing frequency. Effective products include strobilurin fungicides (FRAC 11), Enable® (FRAC 3), Amistar Top® (FRAC 11+3), Pristine® (FRAC 11+7), and copper. Many of these also control other diseases so it is possible to find one that can manage more than one problem. Just verify the timing works well for all of the targeted diseases.

To enhance fungicide efficacy, apply a compost accelerator to leaf litter (50 gal/acre via herbicide boom) and lightly hedge to remove dead wood. Because black spot remains a quarantine disease, ensure all plant material is removed from vehicles and equipment moving between groves to prevent spread. These simple practices can save headaches in new locations.

Melanose Melanose is a disease of dead wood. The causal fungus colonizes dead or live twigs less than ¼ inch in diameter, including fruit stems from the previous season that fail to detach. Leaf and fruit lesions are sterile and do not produce spores. Severe infections can crack and deform fruit and leaves, most often following a freeze.

20 UF/IFAS Citrus Magazine December 2025

Melanose

Credit: Tonya Weeks, UF/IFAS

In spring, the fungus produces many spores on colonized twigs. These spores disperse short distances during rain events, usually splashing downward. In dry weather, the fungus preserves spores in long tendrils, which remain viable for at least a month, ready for rain.

Spores infect susceptible leaves, fruit, and twigs with only 10–12 hours of wetness at 70–80 °F; outside this range, infection may take up to 24 hours. Such wetting periods are common in Florida during spring and early summer.

Grapefruit is by far the most susceptible cultivar and typically the only one requiring routine applications unless there is a freeze. Light hedging to remove dead wood reduces inoculum and improves fungicide performance.

Applications should be made from May through late June or early July. Grapefruit are susceptible from ¼–½ inch diameter until 2.5–3.0 inches. Copper remains the most economical and effective management tool because of its long residual activity. However, copper coverage declines over time due to fruit growth and rainfall erosion, which is why applications are recommended every 21 days. If heavy rain occurs within that interval, residue longevity may be reduced.

Growers can estimate residue persistence using the Citrus Copper Application Scheduler (http:// agroclimate.org/tools/citrus-copper-applicationscheduler/). Copper also helps suppress greasy spot, canker, and black spot.

If phytotoxicity is a concern in hot weather, one application of a non-copper fungicide can be substituted. Recommended alternatives include strobilurin fungicides (FRAC 11), Amistar Top® (FRAC 3+11), or Pristine® (FRAC 7+11). Note that their residual period is shorter, so adjust the spray schedule accordingly.

Alternaria Brown Spot (ABS) Certain tangerine cultivars and hybrids are affected by ABS, while others are resistant. Susceptibility depends on whether the cultivar is sensitive to the host-specific toxin produced by the pathogen. This toxin likely affects mitochondrial function, though the precise target is not fully understood.

Progeny of ‘Dancy’ tangerine are generally susceptible to some degree, while ‘Clementine’ types are resistant.

Hybrids between ‘Dancy’ and ‘Clementine’ may segregate for susceptibility. Historically, Rough Lemon rootstock was also susceptible to a different Alternaria species, but tangerines were not affected by that strain.

Information on newer tangerine cultivars remains limited. ‘Marathon’ is known to be susceptible and will require management, whereas SugarBelle® is not.

Although few susceptible tangerine plantings remain in Florida, some still require management.

For highly susceptible cultivars or groves with a recent outbreak, begin applications as early as early March, when flush is ¼–½ expanded. If spring is wet, a second application at full flush expansion may be necessary.

Managing leaf infections also reduces stem lesions that can kill young twigs.

For optimized timing, consult the ALTER-RATER table in the Florida Citrus Production Guide (https://edis.ifas.ufl. edu/publication/CG021). Growers should be very careful with the selection of fungicides for ABS management.

Widespread strobilurin (FRAC 11) resistance is found in Florida, rendering these fungicides ineffective.

Citrus Scab Since the Florida citrus industry transitioned from field nurseries to covered nurseries, scab incidence has dropped dramatically. This is a success story! However, infections still occasionally occur and require attention.

Citrus scab in Florida is caused by two primary forms: the Florida broad host range (FBHR) and the Florida narrow host range (FBNR) types.

• FBHR infects lemons, grapefruit, Temples, sour oranges, sweet oranges, Satsuma, and many tangerines.

• FBNR infects lemons, grapefruit, and Satsuma only.

Sweet oranges are rarely affected, typically only when adjacent to heavily infected tangerine blocks.

The first line of defense, beyond using clean nursery trees, is pruning out infected limbs, provided they are not a major portion of the canopy. The fungus spreads primarily within the canopy but can occasionally move between trees via wind and rain. It produces spores after 1–2 hours of wetting, and only 5–6 hours of moisture are needed for infection.

Three applications are recommended for effective management, and timing is critical:

Alternaria brown spot Credit: Jamie Burrow, UF/IFAS

A third application should be made at petal fall. For the first three applications, alternate Amistar Top® (FRAC 3+11) and Pristine® (FRAC 7+11) with copper.

Afterward, maintain a protective coating on fruit until mid-July, when fruit are no longer susceptible.

Copper should suffice unless phytotoxicity risk is high, in which case rotate in one of the other fungicides.

1. ¼ flush expansion (late February–early March)– Apply a strobilurin-containing fungicide (FRAC 11), which protects new growth and suppresses sporulation from old lesions.

2. Petal fall–Apply Ferbam® (FRAC M 03) or Enable® (FRAC 3).

3. Two weeks later–Apply copper. Although copper is not particularly effective against scab, this timing overlaps well with control for other diseases such as ABS. If disease levels remain high, rotate to a different mode of action not previously used in the season.

UF/IFAS Citrus Magazine December 2025 21

Career Highlight Chris Oswalt, UF/IFAS Multi-County Extension Agent What inspired you to pursue this career path?

My inspiration came from the family business, though my path wasn’t straightforward. I explored a few directions first—working with the Florida Department of Citrus’s mechanical harvesting project and later at an agri-chemical facility in the late 1970s. Eventually, I decided to focus on citrus production, enrolling at the University of Florida. Near graduation, I was offered a graduate assistantship, which led me to pursue a master’s degree and ultimately a career in Extension work.

Can you describe your first few days on the job? What do you remember most? Was it as per the expectations?

My first Extension job began in May 1988 at the Cocoa office in Brevard County, covering several counties hit hard by the freezes of 1983 and 1985. Fresh out of school, I was eager to share what I thought growers needed—but quickly learned their priorities differed when only one grower showed up to my first meeting.

When I returned in 2001 as the citrus agent for Polk and Hillsborough Counties, ten years in citrus production had given me a better understanding of growers’ needs. What I remember most is how welcoming the growers were. Not everyone agreed with me, but I never had a bad experience working with a citrus grower or researcher.

22 UF/IFAS Citrus Magazine December 2025

What are some of the most significant milestones or achievements in your career?

Some of my most significant career milestones include serving as an executive officer and member of the Florida State Horticultural Society—an organization my family has been part of for generations and where I first published my master’s research. I’ve also been active with the National Association of County Agricultural Agents, earning several professional honors, including the Distinguished Service Award.

Additionally, I contributed to the Citrus Under Protective Screen

(CUPS) project, helping growers successfully adopt new production research and practices.

How has your role in Extension programming and the tools used evolved over the years?

When I first started, Extension programming and tools looked very different. My citrus Extension newsletter was duplicated on a ditto machine—that was our version of mass communication. We used landlines for all phone calls, and the most advanced technology at our disposal was a basic-function calculator.

Computers were large, centralized systems housed in separate buildings, and data was entered using punch cards. Forecasting tools were also rudimentary—we recorded winter weather watch forecasts on a phone answering machine, and only one office computer

could access the actual National Weather Service updates.

How has growers’ approach toward citrus production changed?

Educational outreach required a great deal of manual effort. Presentations were made using 35 mm slides that we photographed ourselves, developed at a camera shop, and then organized in a projector carousel with wired remotes. Preparing a single presentation could take days or even a week. Meeting registration was handled entirely by phone calls to office staff, since digital platforms like Eventbrite were decades away.

While we still rely on proven practices, growing citrus in an HLB environment has forced us to adapt and tailor our methods to each grove’s specific needs and tree responses—one size no longer fits all in Florida citrus production.

Today, the tools of extension programming have transformed completely. Smartphones, digital cameras, and computer software allow us to collect data, create visuals, and build presentations in hours rather than days.

Communication now happens instantly through email, online newsletters, and social media. We can analyze field data on laptops, visualize trends with specialized software, and deliver programs virtually through webinars and online platforms. What once required a team and extensive logistics can now be accomplished by one person with the right digital tools. The evolution of technology has not only changed how we work—it has also made Extension programming faster, more accessible, and far more impactful.

What lessons did you learn that you wish you had known earlier in your career?

One key lesson I learned as a production manager is that while citrus production is a science, applying that science is an art. Research provides the foundation, but each person must adapt it to their own operation— there are many paths to the same destination.

What do you hope your legacy will be?

I hope my legacy is that I provided stability and reliable information to Polk and Hillsborough county growers through some of the citrus industry’s most challenging times. While helping growers rebuild after HLB hasn’t fully materialized, I take pride in supporting them through change and uncertainty.

What are some of your favorite memories from your time in this role?

My favorite memories are the interactions with citrus growers. I’ve learned as much from their shared experiences as from research, and those insights have shaped how I help them. I’ve always valued being a voice for growers when working with regulators and researchers who may not fully understand their needs.

Any advice or suggestions to the growers as you bid farewell?

Still around, just stepping back from Extension duties.

As for advice, I’ve done my share—now I’ll mostly observe and sprinkle in the occasional unsolicited tip.

UF/IFAS Citrus Magazine December 2025 23

Cover Crop Highlight : Daikon radish Sarah Strauss Raphanus sativus (Daikon radish) is a broadleaf cover crop that can produce a large taproot. Daikon radishes are sometimes known as tillage radishes, as the large roots can help break up compacted soil and provide aeration. When daikon radish cover crop is terminated, the taproot provides resources for soil microbes.

Daikon radish Credit: Sarah Strauss, UF/IFAS

Daikon radish Credit: Sarah Strauss, UF/IFAS

While Daikon radish can grow all year in Central and South Florida, it does best during the cooler months and does well during the dry season when there is little rain. However, it is still important to try and plant them before the end of the rainy season, generally in October or early November, to ensure there is sufficient moisture to help them germinate.

Seeding rates for planting Daikon radish as a cover crop generally range from 4—10 lbs/acre.

Daikon radish Credit: Sarah Strauss, UF/IFAS

What’s happening in research?

Will a lower price bring back orange juice demand?

Ariel Singerman Since citrus greening disease was first found in Florida, orange production statewide has declined in almost every season thereafter. As supply began decreasing in 2005, price started to increase to ration demand— as economic theory predicts. Figure 1 illustrates this relationship by displaying Not-From-Concentrate (NFC) orange juice sales, which represent approximately 90% of the use of Florida’s processed oranges, alongside its price. A notable exception to the inverse relationship between price and quantity occurred in the 2019/20 season, when the quantity demanded for orange juice increased—despite a higher price—driven by consumers’ belief that its consumption would boost their immune system in the face of the COVID-19 pandemic.

Research trial data on oxytetracycline (OTC) trunk injections have shown evidence of increased yield and improved quality in processed oranges. Depending on the magnitude of the yield response in commercial groves to OTC—and barring any negative impact from weather events—supply may increase in upcoming seasons. If so, and making the typical economic assumption that everything else will remain constant, price will decrease. A critical question is then whether demand would increase in response to the lower price— and if so, to what extent. The question is particularly relevant because, in the last few years, there have

Figure 1. Not-From-Concentrate orange juice sales quantity and price.

been numerous media and online articles questioning the benefits of consuming orange juice due to its sugar content. Some even argue that consumer preferences have changed as a consequence of those concerns, driving orange juice consumption down. But, as I will explain next, the data show that the decrease in orange juice consumption has been mostly a consequence of the increase in its price.

Transforming the data shown in Figure 1 using natural logarithms to express changes in percentage terms, I constructed Figure 2. Each dot in the figure represents the combination of (inflation-adjusted) price and quantity in each season from 2005/06 to 2022/23.

The red line, estimated by regressing quantity on price, can be interpreted as a downward-sloping demand curve. The fit is quite strong: price explains 94% of the variation in quantity. Also, the price elasticity of demand is estimated at -1.65, indicating that for every 1% increase in price, demand decreased by 1.65%.

While this relationship may not necessarily hold in the future, the estimation provides evidence that the price of orange juice has been the major factor affecting demand. Therefore, it is likely that if the price of orange juice decreases due to an increase in supply, demand will increase.

Figure 2. Combination of Not-From-Concentrate orange juice sales quantity and (inflation-adjusted) price by season.

UF/IFAS Citrus Magazine December 2025 25

What’s happening in research?

A New Chapter for Citrus: Turning Orange Peels into Heart-Healthy Gold Yu Wang and Hyun Jeong Jung Florida’s citrus industry is world-renowned for producing premium orange juice. Yet for every gallon of juice produced, nearly an equal amount of peel is left behind. Traditionally, this material has been used for cattle feed or compost, but new research from the UF/IFAS Citrus Research and Education Center (CREC) suggests a far more valuable use.

Recent studies from our group reveal that orange peel contains bioactive compounds that may help support human heart health. These findings point to an innovative opportunity to transform a processing byproduct into a value-added ingredient with commercial potential.

Understanding the Link Between Citrus and Heart Health Our work focused on a compound called trimethylamine N-oxide (TMAO), which has been identified as a key contributor to heart disease. High levels of TMAO are associated with an increased risk of atherosclerosis, stroke, and other cardiovascular conditions.

TMAO is produced when gut bacteria convert nutrients from red meat and certain energy drinks, particularly L-carnitine, into trimethylamine (TMA), which the liver then converts into TMAO. Elevated

TMAO promotes inflammation and plaque buildup in arteries.

We asked whether natural compounds in orange peel could interrupt this process. Citrus peels are rich in flavonoids and phenolic acids known to influence metabolism and inflammation, making them ideal candidates for study.

Discovering a Powerful Natural Inhibitor To explore this idea, we separated orange peel into two extracts: Oil-based (nonpolar) solvents and Waterbased (polar) solvents. Each contained distinct sets of natural compounds. The water-based extract proved far more effective at reducing TMA and TMAO levels in both laboratory and animal studies, indicating that the most active compounds are water-soluble.

Using metabolomics, a powerful technique for analyzing complex mixtures, we identified one compound that stood out: feruloylputrescine. This molecule acts as a natural inhibitor of bacterial enzymes that form TMA. Unlike antibiotics, which can disrupt beneficial gut microbes, feruloylputrescine works selectively, preventing harmful bacterial activity while maintaining a healthy microbiome balance.

Effect of orange peel extract on heart disease indicators. Created by BioRender.com

26 UF/IFAS Citrus Magazine December 2025

Promising Results in Laboratory Studies In animal trials, diets supplemented with orange peel extracts or purified feruloylputrescine led to:

value, from juice and essential oils to flavor compounds and health-promoting molecules. Such innovation strengthens both the economic resilience and sustainability of Florida citrus.

• Lower blood and urine TMA/TMAO levels

Science with a Purpose

• Reduced inflammation

Our research also demonstrates how advanced science can serve practical goals for Florida agriculture. Through technologies such as liquid chromatography, mass spectrometry, and metabolomics, we are uncovering compounds that connect agricultural production with human health benefits. This farm-to-function approach not only strengthens the scientific foundation of citrus research but also creates new opportunities for growers and industry partners.

• Improved cardiovascular markers Even when animals consumed a high-fat diet, feruloylputrescine maintained its protective effects, suggesting a strong potential for promoting heart health.

These findings highlight a new dimension in citrus research, revealing that compounds within orange peel can influence human health in ways previously unrecognized. The discovery of feruloylputrescine demonstrates that natural products from citrus not only contribute to flavor and aroma but may also hold potential for disease prevention and wellness applications.

Turning Waste into Value For Florida’s citrus industry, these discoveries could represent a new revenue stream. Citrus processing plants already handle large volumes of peel, and the infrastructure for collection and drying is well established. If the extraction and purification of feruloylputrescine can be integrated into existing systems, peel could become a profitable source of functional ingredients for foods, beverages, or nutraceuticals.

This concept supports the vision of a “citrus biorefinery” where every part of the fruit contributes

Looking Ahead Florida’s citrus growers have always shown resilience and innovation in the face of challenges. Discoveries such as feruloylputrescine reaffirm the renewed potential of the state’s signature crop. This study reminds us that even familiar materials like orange peel can yield surprising possibilities when examined through the lens of modern science and technology.

Peel may have started as a byproduct, but it is quickly becoming part of a bigger story for Florida citrus.

Finding new value in what was once waste helps keep the industry strong and competitive, while showing consumers that citrus can contribute to both a healthy lifestyle and a sustainable future.

Acknowledgment: The research team gratefully acknowledges Uncle Matt’s Organic for providing the citrus peel materials used in this study.

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March 16-18, 2026

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The 4th International Flavor Summit: A Gathering of Industry Perspectives is a biennial event for professionals, academia, students, and anyone interested in the latest trends and discoveries in the world of flavor science.

Hosted by the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Citrus Research and Education Center, this three-day conference brings together leading researchers and practitioners working in flavor science across the food, beverage, and health sectors.

Find out more at: conference.ifas.ufl.edu/flavorsummit

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Faculty Spotlight: Stephanie Brown

UF/IFAS State Specialized Extension Agent, Food Science Can you briefly describe your current Extension program?

I develop, implement, and evaluate Extension programs that help Florida’s food processors and entrepreneurs comply with food safety regulations and build and maintain successful businesses.

What are you most passionate about in your Extension program?

As a lifelong learner, I’m passionate about translating food-safety and value-added processing advances into practical, real-world practices for the food system.

I love meeting people where they are whether it’s helping startups or larger operations grow.

What’s a project you’re especially proud of?

Through great partnerships, I helped turn a shared kitchen closure into a new program by relocating testing supplies and launching in-person technical support opportunities.

How has your program evolved?

Since joining UF/IFAS, my programs have evolved iteratively through client feedback and policy shifts.

This includes expanding trainings, one-on-one support, and practical resource development. This approach helps producers stay compliant and ready to innovate.

What is your teaching philosophy?

Applied, learner-centered, and outcome-driven. I start with industry problems, translate the science into practical steps, and use different teaching tools until people feel confident. I judge success by what learners do next and adapt based on feedback.

What’s the most exciting part of your work?

The most exciting part is the daily variety, with no two days ever being the same. The constant change keeps me learning and helps me deliver tangible outcomes including improved regulatory compliance, safer products, and new innovations in the food system.

What’s been the biggest challenge in your program, and how did you Credit: Stephanie Brown, overcome it?

UF/IFAS Covering a big state with diverse producers and commodities is challenging because needs and schedules differ. To address this, I used a needs assessment to prioritize gaps, build partnerships, and will deploy a train-the-trainer approach to deliver core materials.

How do you come up with new ideas for presenting your information?

I generate ideas by learning from colleagues and program evaluations. When possible, I use multimodal delivery including hands-on practice, visuals, and scenarios. I also offer one-on-one support outside of trainings to tailor content for those who prefer this method.

What tools or techniques are essential to your work?

People and partnerships, a computer, and a vehicle are essential. These are needed to continue to co-develop solutions with stakeholders and deliver trainings across Florida.

What’s the weirdest or most unexpected thing that’s happened during your Extension work?

The most unexpected thing has been realizing that a single point of clarification can save weeks.

Small regulatory misunderstandings derail production and waste resources, so clear guidance is priceless.

Credit: Jessica Ryals, UF/IFAS Credit: Worth Brown

What’s happening in research?

Somatic Cybridization in Citrus: A New Frontier for Disease-Resistant Cultivars Ahmad Omar, Flavia Zambon, and Jude Grosser Promising Tool for Citrus Growers

What are cybrids?

Citrus growers have long faced the challenge of balancing fruit quality with disease resistance.

With persistent threats such as citrus canker and huanglongbing (HLB) continuing to devastate groves, the need for innovative, durable solutions has never been greater.

Cybrids, or cytoplasmic hybrids, are plants that combine the nuclear DNA of one parent with the mitochondrial and/or chloroplast DNA of another.

One promising approach is somatic cybridization, a biotechnology technique that allows researchers to enhance disease resistance in existing citrus varieties without changing the fruit’s appearance or taste.

Developed and refined at the UF/IFAS Citrus Research and Education Center (CREC), this method enables the introduction of beneficial traits from disease-tolerant species into known commercial cultivars. The resulting plants, called cybrids, retain the same desirable characteristics that growers and consumers already recognize and love.

In citrus, cybrids are created through protoplast fusion (Figure 1), where cells from two different species or varieties are merged. One parent provides the nucleus (which determines the plant’s main characteristics), while the other contributes organelles, like mitochondria and chloroplasts, which can influence disease resistance and other traits.

This process was discovered by accident while researchers were attempting to create somatic hybrids.

We discovered that some regenerated plants looked identical to one parent but carried organelle DNA from the other. These were later confirmed to be cybrids, and the discovery opened an entirely new avenue for citrus improvement.

From Serendipity to Strategy The first commercial success story from this work came from an unexpected source. While trying to create triploid hybrids, we fused protoplasts from ‘Dancy’ mandarin with pollen cells from ‘Pink Marsh’ grapefruit. The result was N228 ‘Summer Gold’ grapefruit (Figure 2), a new variety with higher sugar content and a longer harvest window than traditional Ruby Red grapefruit.

Encouraged by these results, the CREC plant improvement team began designing specific combinations to target key diseases. One particularly promising example is a cybrid of ‘Dancy’ tangerine with Satsuma cytoplasm.

Figure 1. Illustration of protoplast fusion in citrus.

Created by BioRender.com

UF/IFAS Citrus Magazine December 2025 29

To confirm these findings, our team propagated new trees from Cybrid #3 and subsequently tested them using quantitative PCR (qPCR). The results were astonishing: no detectable HLB bacteria in any of the 19 tested trees.

What does this mean for growers?

Figure 2. N2-28 ‘Summer Gold’ grapefruit.

Credit: Jude Grosser, UF/IFAS

While ‘Dancy’ is valued for its exceptional flavor, it is extremely susceptible to Alternaria brown spot. The cybrid version, however, has shown complete resistance to Alternaria for more than 15 years in the field and displays tolerance to HLB. This new ‘Dancy’ clone has now been released for commercialization.

Targeting Canker and HLB Our team also explored whether cytoplasm from ‘Meiwa’ kumquat, known for its canker resistance, could improve grapefruit’s tolerance to the disease.

We created 144 cybrid plants using protoplasts from three grapefruit varieties and ‘Meiwa’ kumquat.

All the resulting plants looked like grapefruit, and all had the ‘Meiwa’ mitochondrial genome.

However, the chloroplast genome in the cybrids was randomly inherited.

When tested in greenhouse assays, cybrids with grapefruit chloroplasts remained susceptible to canker. However, those with both mitochondrial and chloroplast DNA from ‘Meiwa’ showed significantly improved tolerance, with some even showing resistance.

These promising results led to field trials under realworld conditions, including high disease pressure and environmental stress.

If these findings continue to hold, Cybrid #3 could represent a breakthrough for both HLB and canker management. The ability to grow high-quality grapefruit with built-in disease resistance, without using genetic modification, offers a powerful new tool for sustainable production.

This same approach can be extended to other commercially important yet disease-prone varieties, allowing breeders to preserve the fruit’s desirable characteristics while improving its resilience.

Looking Ahead The next research step is to confirm that Cybrid #3 produces true-to-type fruit. To accelerate this process, our team has topworked advanced budwood onto mature rootstocks at the Lake Alfred research center.

If the fruit quality matches expectations, this will mark a major milestone toward the commercial release of disease-tolerant grapefruit cultivars.

Somatic cybridization represents a new frontier for citrus breeding, a precise, non-GMO method that merges the strengths of different citrus species. It holds great promise for helping growers combat HLB, canker, and other persistent challenges while keeping the fruit just the way we love it.

Acknowledgment: We thank the Scott Family for assisting in this project by hosting the cybrids in their grove.

Field Trials and Unexpected Challenges The field trials were anything but smooth. The first planting suffered damage from misapplied herbicide, halting tree growth. After repropagation and replanting, the second site experienced saline irrigation water, causing widespread decline across the grove.

Despite these setbacks, one tree, Cybrid #3, derived from the N11-11 Ruby somaclone, stood out (Figure 3). It not only survived but thrived, showing no signs of canker or HLB, despite having initially tested positive for HLB. This tree had the ‘Meiwa’ chloroplast genome, suggesting a strong link between organelle DNA and disease resistance.

30 UF/IFAS Citrus Magazine December 2025

Figure 3. (A) Ruby somaclone N11-11 Cybrid #3 tree impacted by saline irrigation water and (B) transplanted Cybrid #3 tree to a location irrigated with well water. Credit: Ahmad Omar, UF/IFAS

FAWN

Florida Automated Weather Network

Providing weather data for Florida’s agriculture stakeholders https://fawn.ifas.ufl.edu

What’s happening in research?

Genetic Transformation Offers Hope Against Huanglongbing Manjul Dutt and Zhonglin Mou Introduction Huanglongbing (HLB), or citrus greening, remains one of the most destructive diseases facing the citrus industry today. In Florida, it has caused devastating losses in acreage and productivity. Conventional approaches, such as enhanced grove management and vector control, can help prolong the life of infected trees, but they do not offer a permanent solution.

The most effective long-term strategy for managing HLB is to develop citrus trees that are tolerant or resistant to the disease. Traditional breeding has made progress toward this goal, but it is slow and unpredictable.

Most citrus varieties have long juvenile periods, and hybridization often introduces unwanted traits along with desirable ones, especially when using HLB-tolerant relatives. It can take several generations of selection to eliminate undesirable traits while maintaining HLB tolerance in conventionally developed hybrids.

Modern genetic techniques, particularly genetic transformation, offer a more precise way to introduce resistance into commercial varieties. This approach allows researchers to add specific, well-characterized genes that enhance HLB tolerance or resistance, while preserving the fruit quality and variety traits growers and consumers already value.

What is genetic transformation?

Genetic transformation is a process in which a specific gene is added to a plant’s DNA to improve a targeted trait such as disease resistance, drought tolerance, or fruit quality. Unlike traditional breeding, transformation does not shuffle all the genes from two parent plants.

Instead, it introduces only one or a few well-defined genes into the existing variety, keeping the rest of the variety unchanged.

For citrus growers, this means that favorite varieties such as ‘Hamlin’, ‘Valencia’, and ‘Ruby Red’ could retain their fruit quality and yield, but with added protection against HLB.

How does transformation differ from traditional breeding?

Both transformation and traditional breeding aim to create better, more productive trees. However, they differ in how they alter the plant’s genetics: • Similarity: Both methods result in heritable improvements that can be passed to future generations.

• Difference: Traditional breeding mixes the entire genetic makeup of two parents, producing offspring that may have both beneficial and undesirable traits. Transformation is more targeted, allowing the introduction of just one specific gene without changing other characteristics of the variety.

In other words, traditional breeding is like shuffling two complete decks of cards, while transformation is like carefully adding one winning card to a hand you already like.

Why does Florida need genetic transformation?

Florida’s citrus industry continues to face unprecedented challenges from HLB. Despite decades of effort, no cure exists, and current management practices only slow the disease’s impact. Genetic transformation provides a path forward by directly introducing disease-resistance genes into existing commercial varieties, creating trees better equipped to survive and produce fruit in HLBendemic environments.

Researchers can also draw upon the wealth of genetic information available from other plants.

Resistance genes from well-studied species such as Arabidopsis and rice have been characterized in detail, allowing scientists to identify promising candidates for transfer into citrus. This cross-species approach greatly accelerates the search for effective resistance genes.

How does genetic transformation work?

The most common and effective method for citrus

32 UF/IFAS Citrus Magazine December 2025

transformation uses a naturally occurring soil bacterium, Agrobacterium tumefaciens. In nature, this bacterium transfers part of its DNA into plants, a process that has been occurring for millions of years.

Researchers have harnessed this natural ability for agriculture. Instead of inserting genes that cause plant tumors (crown gall disease), scientists guide Figure 1. The process of developing genetically modified (GM) citrus trees.

Agrobacterium to deliver beneficial Created by BioRender.com genes, such as those that improve 3. Regulatory Review (2–3 years): disease resistance. In this way, a natural process is Candidate varieties are submitted to redirected toward valuable outcomes. the USDA, EPA, and FDA for independent safety evaluations, and to the Florida Budwood Program to Other transformation methods, such as gene gun ensure they are disease-free and true to type. technology, which shoots DNA-coated particles into cells, and protoplast transformation, which introduces DNA into isolated cells, are also available. However, 4. Commercial Release (2–3 years): Once approved, new GM citrus varieties are Agrobacterium-mediated transformation remains the propagated on a large scale and made available most efficient and widely used approach for citrus. to growers.

The process works in four main steps (Figure 1): Are GM citrus trees safe?

1. Small pieces of citrus tissue (often stems) are YES. Before any GM citrus tree can be planted exposed to Agrobacterium carrying the new gene. commercially, it must pass rigorous safety evaluations to ensure it is equivalent to conventional varieties in 2. The bacterium transfers the gene into the growth, fruit quality, and environmental safety. citrus DNA. 3. These modified cells are grown into whole plants in the lab.

4. The new plants are tested in greenhouses and fields to confirm that they resist or tolerate HLB and grow normally.

Steps in Developing Genetically Modified (GM) Citrus The process of creating a genetically modified (GM) citrus tree generally takes 8–12 years from gene discovery to commercial release (Figure 1).

1. Gene Identification and Lab Work (1–2 years): Scientists identify promising resistance genes, insert them into citrus tissue, and verify expression in the lab.

2. Greenhouse and Field Testing (3–7 years): The best candidates are propagated and evaluated for HLB tolerance. Trees derived from juvenile tissue may take 5–7 years to bear fruit, while those from mature tissue can produce fruit in as little as two years.

Key requirements include: • The trees must grow and perform normally in the field.

• The fruit must be safe to eat and comparable in taste, nutrition, and quality.

• The trees must not have negative effects on the environment.

In the U.S., safety assessments are conducted independently by the USDA, EPA, and FDA. Only after all three agencies approve can a GM citrus variety be released for commercial production.

Genetically modified crops are not new. Examples such as the papaya Arctic® apple (which resists browning), disease-resistant bananas, and longestablished corn, and soybean varieties have been safely grown and consumed worldwide for decades.

These examples show that when carefully developed and regulated, GM crops can be as safe as conventional ones, while offering valuable new traits for growers and consumers alike.

UF/IFAS Citrus Magazine December 2025 33

What’s happening in research?

Helping Florida Citrus Growers Through Mighty Collaboration Charlie Messina and Michael Rogers The Citrus Research and Education Center (CREC) is more than 100 years old and is the largest University of Florida off-campus research station. Since its establishment, the CREC has served the citrus industry by advancing Research, Extension, and Teaching programs to meet growers’ needs.

Since the discovery of HLB in Florida groves, CREC scientists have worked tirelessly to find solutions to this devastating disease. Their multi-disciplinary approach has included improved horticultural practices, plant protection strategies, and genetic modification of citrus varieties. These efforts have given growers practical tools to adapt their operations and better manage HLB while long-term solutions are pursued. Today, growers have access to technologies such as antibiotic applications, improved horticultural practices, and promising new citrus varieties with varying levels of HLB tolerance. Still, because HLB remains a challenge, additional efforts and investments are needed to speed progress toward a lasting solution.

Launching the Crop Transformation Center (CTC) Following discussions among Florida citrus leaders including Scott Angle, Matt Joyner, Morgan McKenna Porter, Emery Smith, and others, UF/IFAS, supported by the UF president’s office, the Florida Department of Citrus, and the Citrus Research and Development Foundation, launched the UF/IFAS Crop Transformation Center (CTC) in Gainesville.

The CTC’s mission is “to accelerate genetic gain for specialty crops to improve human and environmental health.” While the CTC will eventually expand into areas like turfgrass and row crops, its current priority is citrus and the fight against HLB.

Credit: Tonya Weeks, UF/IFAS

The CTC advances main functions:

its

mission

through

three

• Research and development pipeline–The center manages stakeholder investments and helps move ideas from concept to solutions for growers. This includes overseeing a pipeline of potential gene edits and transgenics, with balanced investments in plant transformation, nursery tree production, field evaluation, and regulatory needs.

• Service platforms–By centralizing services, the CTC allows scientists to focus on discovery. Citrus transformation work takes place primarily in the citrus transformation facilities already established at the CREC, with additional labs assisting as needed. The center also coordinates regulated field evaluations, with CREC, led by scientists from the CREC. In addition, the CTC provides IFAS leadership in regulatory science and compliance.

• Collaboratory–The CTC fosters collaboration among scientists from multiple disciplines— molecular biology, horticulture, entomology, plant pathology, breeding, economics, and more. Geneedited and transgenic crops cannot be developed in isolation; success depends on this kind of “mighty collaboration.”

How do CTC and CREC work together?

The partnership between CTC and the CREC did not form overnight. It has taken time to align capabilities, expertise, and resources into a unified system that functions as a “collective mind and body.”

This system works in cycles:

A

B

1. Discovery–Scientists identify promising genes and methods for transformation and gene editing. Recently hired scientists Dr. Huo (transformation) and Dr. Baysal (gene editing) bring additional specialized expertise to the CTC in Gainesville, while CREC scientists continue ongoing work identifying gene targets for HLB resistance/tolerance.

2. Transformation–Identified gene targets are then transformed in the juvenile and mature tissue transformation labs at the CREC. 3. Evaluation–Plants are then returned to the discovery scientists (Gainesville/CREC) for accelerated growth and testing. Promising lines are then tested in regulated field sites overseen by CREC scientists.

Figure 1. Iterative learning cycle of Research and Development (A) that led to the first set of Bt transformed scion events microgragted onto immature citrus rootstocks transformed at CREC with Bt proteins designed at CTC (B). These plants will be grown at UF Gainesville in indoor agriculture facilities and sent back to CREC for field testing. Panel (A) generated using ChatGPT. Credit: UF/IFAS

4. Feedback–Scientists analyze results, share findings with growers, and use the feedback to inform the next cycle of innovation.

While the process can vary, this workflow demonstrates how the CTC and CREC combine their strengths to move solutions from the lab to the grove.

Expanding Collaboration Beyond Florida HLB is not just a Florida problem; it is a hemispheric threat. Even if Florida finds solutions, new insect introductions from Central or South America could undermine progress. Recognizing this, UF/IFAS CTC and FONTAGRO (https://fontagro.org/en) coorganized an online workshop on September 9–10, 2025.

The event brought together UF scientists from multiple disciplines, USDA researchers, and partners from South America and Brazil.

Together, they developed a blueprint for addressing HLB at a hemispheric scale.

This blueprint will guide funding efforts for a coordinated project that spans detection, field evaluations, regulatory approval, and grower outreach—another example of how collaboration is essential to tackling HLB. UF/IFAS Citrus Magazine December 2025 35

Cultivar Highlight : ‘Marathon’ Mandarin (formerly 1420) John Chater • Origin: ‘Marathon’ mandarin is a cultivar selected from a 2005 cross between ‘Daisy’ and ‘Seedless Kishu’ developed by Dr. Fred Gmitter. It was released by the UF/IFAS Plant Improvement Team around 2019.

• Harvest Timing: Harvest typically occurs in October, though fruit quality should be monitored beginning in September. Fruit set this season has been adequate on mature trees grafted to sour orange in Polk County and on US-897 in CUPS (Citrus Under Protected Screen) systems after cropping. Cropping consistency can vary, and it is not yet known whether the cultivar exhibits alternate bearing. Rootstock effects on both yield and fruit quality are still under evaluation.

• Tree Health and Growth: ‘Marathon’ appears to maintain good tree health in HLB-affected environments at multiple locations (including Polk and Lake Counties) across several rootstocks (sour orange, orange 14, UFR-5, and an additional unreleased rootstock candidate).

Trees develop large, vigorous canopies and gain significant height and biomass over time.

• Fruit Size and Quality: In HLB conditions, average fruit size ranges from 2.1 to 2.4 inches, increasing to 2.8 inches in CUPS systems.

Average soluble solids (°Brix) measured in Lake Alfred trials range from 9.0 to 10.7 °Brix, and up to 11.9 °Brix in CUPS conditions in Central Florida.

• Fruit Characteristics and Management: ‘Marathon’ fruit are seedless and easy to peel, making them well-suited for the fresh market.

However, the cultivar is susceptible to Alternaria brown spot, which can significantly reduce marketable yield if not properly managed. Fruit may exhibit granulation at the stem end (“dry tops”), particularly in early cropping years on young trees and in mature trees later in the season. Ongoing evaluations are investigating how rootstock choice and oxytetracycline (OTC) trunk injections influence granulation incidence.

Marathon fruit

Credit: Tonya Weeks, UF/IFAS

‘Marathon’ on orange 14 in Lake County, Florida, was planted in October 2021, now four years old.

Credit: John M. Chater, UF/IFAS

Rootstock Highlight : Orange 14 John Chater

• Origin: Orange 14 is an allotetraploid zygotic hybrid (“tetrazyg”) rootstock developed by Dr. Jude Grosser through the UF/IFAS Citrus Improvement Program. It originated from a conventional cross between two somatic hybrids previously created via protoplast fusion. The somatic hybrid seed parent is ‘Nova’ mandarin hybrid + ‘Hirado Buntan’ pummelo (zygotic seedling), and the pollen parent is Cleopatra mandarin + Argentine trifoliate orange.

Orange 14 rootstock Credit: Jude Grosser, UF/IFAS

• Disease Tolerance and Field Performance: Orange 14 has demonstrated tolerance to Phytophthora in Florida trials and shows good tree health when budded with sweet orange scions at multiple sites in Polk County (including Lake Alfred and Haines City) using OLL budlines.

• Tree Growth and Yield: Trees grafted on orange 14 generally develop a medium- to full-sized canopy. Early observations suggest promising productivity and fruit quality performance, though long-term data collection is ongoing. In a demonstration block in St. Cloud, Florida, six-year-old OLL-8 trees on orange 14 produced approximately 3.5 boxes per tree over two years under HLB conditions.

• Availability: This rootstock has been newly approved for commercial release and is now available to Florida citrus growers through licensed nurseries.

CITRUS ADVISORY SYSTEM Get the current on postbloom fruit drop (PFD) disease risk in your local area.

http://agroclimate.org/tools/cas/

What’s happening in research?

Early Performance of New Citrus Rootstock Cultivars Ariel Singerman, Kim Bowman, and Danelle Seymour This article provides estimates for the performance of ‘Valencia’ sweet orange grafted on new hybrid citrus rootstock cultivars, developed by the Agricultural Research Service (ARS) of the U.S. Department of Agriculture (USDA). These estimates can help growers decide which rootstocks to plant in huanglongbing (HLB)-endemic regions affected by Candidatus Liberibacter asiaticus (CLas). Notably, the analysis combines yield and economic performance.

Our data consist of annual yields collected in a large, replicated trial conducted at the USDA Picos Farm located in Fort Pierce, Florida. The trial consisted of a total of 50 rootstocks that included Swingle, sour orange, Cleopatra, and ridge orange as standard rootstocks used in Florida for comparison. Trees were planted in 2014 using a randomized block statistical design with a planting density of 640 trees per hectare (approximately 260 trees per acre). Yield data were collected over six seasons.

Rootstock

Year 3

Year 4

Year 5

We calculated yield differences between each rootstock and sour orange because sour orange had the highest yield among the standard rootstocks in the trial. In addition, we used regression analysis to determine which of the differences were statistically significant. Table 1 lists the 13 rootstocks that attained positive cumulative pounds solids per acre differences, with respect to sour orange over six seasons after production began. In the table, the asterisks next to the estimates denote statistical significance. One, two, and three asterisks indicate the results are statistically significant at the 10%, 5%, and 1% level, respectively, that is more asterisks indicate stronger evidence. The rootstocks with the largest cumulative difference in pounds solids per acre are US SuperSour 4 and US SuperSour 5, which yielded 638 and 361 pounds solids per acre more over six seasons relative to sour orange, respectively. For both rootstocks, the differences with respect to sour orange are largest (and statistically significant) in Years 4 and 6.

Year 6

Year 7

Year 8

Cumulative over 6 seasons

Difference of Pound Solids per Acre Relative to Sour Orange US SuperSour 4

20.85

291.11 ***

64.72

148.19 **

55.91

56.85

637.63

US SuperSour 5

10.81

149.06 ***

39.78

100.10 **

30.87

29.94

360.56

US-1672

98.83

126.40

27.77

-14.46

94.67

-29.46

303.76

US-1676

113.28

68.18

10.60

130.99 ***

-16.74

-14.40

291.91

US SuperSour 3

40.44

269.83 ***

-43.79

-71.79

82.03

11.04

287.76

US-2338

-0.46

158.99 ***

85.44

10.13

22.71

-34.22

242.61

US-2111

-28.40

201.62 ***

58.91

-4.84

-7.93

-38.39

180.97

US-2109

76.79

151.05 **

-86.68

-11.16

19.80

-21.00

128.81

US-1649

10.77

129.48 *

12.98

52.47

-63.43

-38.16

104.10

US-1687

-49.20

118.35

-53.74

62.79

14.54

-5.52

87.22

US-2137

26.66

78.23

-30.68

36.07

36.16

-74.48

71.96

US-1673

112.73

43.68

-2.63

-29.69

-35.40

-58.89

29.80

US-2336

74.47

164.23

-61.89

-48.67

-20.88

-93.64

13.63

Table 1. Rootstocks with positive cumulative differential pound solids per acre relative to sour orange.

Note: One, two, and three asterisks indicate the results are statistically significant at the 10%, 5%, and 1% level, respectively, that is more asterisks indicate stronger evidence.

38 UF/IFAS Citrus Magazine December 2025

Rootstock

Year 3

Year 4

Year 5

Year 6

Year 7

Year 8

Cumulative over 6 seasons

Difference in Revenue Relative to Sour Orange ($/Acre) US SuperSour 4

91.94

1209.26

211.85

480.23

154.47

159.71

2,307.46

US SuperSour 5

47.65

619.18

130.22

324.41

85.30

84.10

1,290.85

US-1672

435.86

525.06

90.92

-46.85

261.53

-82.76

1,183.77

US SuperSour 3

178.32

1120.88

-143.33

-232.66

226.63

31.01

1,180.85

US-1676

499.56

283.23

34.70

424.49

-46.25

-40.45

1,155.29

US-2338

-2.01

660.46

279.69

32.84

62.75

-96.11

937.62

US-2111

-125.26

837.54

192.85

-15.70

-21.91

-107.85

759.67

US-2109

338.65

627.45

-283.73

-36.15

54.71

-58.99

641.94

US-1649

47.49

537.84

42.50

170.04

-175.24

-107.20

515.42

US-2137

117.55

324.98

-100.43

116.89

99.90

-209.22

349.68

US-2336

328.44

682.19

-202.59

-157.72

-57.67

-263.05

329.59

US-1687

-216.99

491.63

-175.91

203.50

40.17

-15.50

326.89

US-1673

497.15

181.43

-8.60

-96.22

-97.79

-165.44

310.54

Table 2. Rootstocks with positive cumulative differential revenue per acre relative to sour orange.

Note: Revenue each season was compounded using a 10% interest rate to express the cumulative value in 2022-dollar terms.

To explore the reasons behind the larger yield differences in Years 4 and 6, we compare the yield of US SuperSour 4 and US SuperSour 5 to sour orange in Figure 1. It is clear that in Year 4, US SuperSour 4 and US SuperSour 5 perform substantially better compared to the previous year, whereas the performance of sour orange increases only moderately. In Year 6, US SuperSour 4 and US SuperSour 5 perform better compared to the previous year (although not as much as in Year 4), while the yield of sour orange decreases relative to the previous year. Notably, in Years 7 and 8, the yield differences between the US SuperSours and sour orange become smaller; yield of all the three rootstocks change by a similar magnitude in Year 8.

Table 2 shows the differences in revenue between each rootstock in the trial and sour orange. To obtain

Credit: Adobe Stock

these estimates, we multiplied the differences in yield shown in Table 1 by the corresponding delivered-in price in each of the seasons, as reported by the Florida Department of Citrus. However, because the price in 2019/20 (Year 6) was particularly low–due to Florida processors having contracts with suppliers in Brazil and Mexico–we used the average price of the three previous seasons for that year only, to better represent more typical market conditions. The prices were $2.74, $2.84, $2.46, $2.68, $2.51, and $2.81 per pound solids, respectively. Table 2 shows that US SuperSour 4 and US SuperSour 5 attained cumulative revenue differences over six seasons (expressed in 2022-dollar terms and using a 10% interest rate) of $2,307 and $1,291 per acre, respectively, compared to sour orange.

Summary We analyzed annual yield data over six seasons to obtain estimates of the performance of ‘Valencia’ sweet orange grafted on new citrus rootstock cultivars developed by ARS-USDA. We found that thirteen of the new hybrid rootstocks attained a positive cumulative yield difference relative to sour orange. The top two rootstocks were US SuperSour 4 and US SuperSour 5, which became commercially available following official release by USDA in 2023. While the differences between the top rootstocks and sour orange become smaller in later years-suggesting that the advantage of the new rootstocks may decrease over time-these early differences are still valuable, as they can lead to a quicker payback period and a higher return on investment when establishing a new grove.

Acknowledgement: This research was funded by USDA NIFA ECDRE award # 2023-70029-41305.

Figure 1. Yield of rootstocks US SuperSour 4, US SuperSour 5, and sour orange grafted with ‘Valencia’ sweet orange scion.

Contributng Author Ute Albrecht Lauren Diepenbrock UF/IFAS Southwest Florida UF/IFAS Citrus Research Research and Education and Education Center Center Manjul Dutt Kim Bowman UF/IFAS Citrus Research USDA Horticultural and Education Center Research Laboratory, Jude Grosser Ft. Pierce UF/IFAS Citrus Research Stephanie Brown and Education Center UF/IFAS Southwest Florida Alissa Hevesh Research and Education UF/IFAS Extension Center Highlands County John Chater Hyun Jeong Jung UF/IFAS Citrus Research UF/IFAS Citrus Research and Education Center and Education Center Megan Dewdney Davie Kadyampakeni UF/IFAS Citrus Research UF/IFAS Citrus Research and Education Center and Education Center

40 UF/IFAS Citrus Magazine December 2025

Ramdas Kanissery Danelle Seymour UF/IFAS Southwest Florida University of California, Research and Riverside Education Center Ariel Singerman Charlie Messina UF/IFAS Citrus Research UF/IFAS Gainesville and Education Center Kelly Morgan (Emeritus) UF/IFAS Gainesville Zhonglin Mou UF/IFAS Gainesville Ahmad Omar UF/IFAS Citrus Research and Education Center Chris Oswalt UF/IFAS Extension Polk County Michael Rogers UF/IFAS Citrus Research and Education Center

Sarah Strauss UF/IFAS Southwest Florida Research and Education Center Tripti Vashisth UF/IFAS Citrus Research and Education Center Yu Wang UF/IFAS Citrus Research and Education Center Flavia Zambon UF/IFAS Indian River Research and Education Center

North Florida Research and Education Center

The North Florida Research and Education Center is one of the largest and most diverse units of UF/IFAS, consisting of research and education campuses in Live Oak, Quincy, and Marianna. The research and Extension citrus programs at NFREC are designed to help develop the cold-hardy citrus industry in North Florida by improving cold protection management and preventing the spread of harmful pests and diseases.

https://nfrec.ifas.ufl.edu UF/IFAS Citrus Magazine December 2025 41

Extension Agents Madelyn Greathouse Sumter, Pasco, and Hernando Counties mgreathouse@ufl.edu Edwin Gutierrez DeSoto, Hardee, and Manatee Counties edwingr@ufl.edu

Alissa Hevesh Highlands County ahevesh@ufl.edu

Amir Rezazadeh St. Lucie County amir2558@ufl.edu

Danielle Williams Gadsden County dsprague@ufl.edu

Chris Oswalt Hillsborough and Polk Counties wcoswalt@ufl.edu

Matt Smith Lake and Orange Counties smith197@ufl.edu

Mongi Zekri Charlotte, Collier, Glades, Hendry, and Lee Counties maz@ufl.edu

Research Faculty Ute Albrecht ualbrecht@ufl.edu

Larry Duncan lwduncan@ufl.edu

Xavier Martini xmartini@ufl.edu

Lukasz Stelinski stelinski@ufl.edu

Fernando Alferez alferez@ufl.edu

Manjul Dutt manjul@ufl.edu

Kimberly Morgan kimorgan@ufl.edu

Sarah Strauss strauss@ufl.edu

Yiannis Ampatzidis i.ampatzidis@ufl.edu

Choaa El Mohtar mohtarc@ufl.edu

Zhonglin Mou zhlmou@ufl.edu

Eric Triplett ewt@ufl.edu

Ozgur Batuman obatuman@ufl.edu

Svetlana Folimonova svetlana@ufl.edu

Taylor O’Bannon taylorlangford@ufl.edu

Nikolaos Tziolas ntziolas@ufl.edu

Bryony Bonning bbonning@ufl.edu

Fred Gmitter fgmitter@ufl.edu

Ahmad Omar omar71@ufl.edu

Tripti Vashisth tvashisth@ufl.edu

Stephanie Brown stephaniebrown@ufl.edu

Claudio Gonzalez cfgonzalez@ufl.edu

Dean Pringle td.pringle@ufl.edu

Christopher Vincent civince@ufl.edu

Tom Burks tfburks@ifas.ufl.edu

Jude Grosser jgrosser@ufl.edu

Nicole Quinn nicole.quinn@ufl.edu

Tara Wade tara.wade@ufl.edu

Michael Burton burton.m@ufl.edu

Sandra Guzmán Jawwad Qureshi sandra.guzmangut@ufl.edu jawwadq@ufl.edu

Nian Wang nianwang@ufl.edu

Liliana Cano lmcano@ufl.edu

Davie Kadyampakeni dkadyampakeni@ufl.edu

Mark Ritenour ritenour@ufl.edu

Yu Wang yu.wang@ufl.edu

José Chaparro jaguey58@ufl.edu

Ramdas Kanissery rkanissery@ufl.edu

Michael Rogers mrgrs@ufl.edu

Alan Wright alwr@ufl.edu

John Chater jchater@ufl.edu

Nabil Killiny nabilkilliny@ufl.edu

Arnold Schumann schumaw@ufl.edu

Flavia Zambon f.zambon@ufl.edu

Michelle Danyluk mddanyluk@ufl.edu

Mark Kistler mark.kistler@ifas.ufl.edu

Muhammad Shahid mshahid@ufl.edu

Megan Dewdney mmdewdney@ufl.edu

Amit Levy amitlevy@ufl.edu

Ariel Singerman singerman@ufl.edu

Lauren Diepenbrock ldiepenbrock@ufl.edu

Graciela Lorca glorca@ufl.edu

Kirsten Pelz-Stelinski pelzstelinski@ufl.edu

Florida Citrus Production Guide The latest recommendations from UF/IFAS

SCAN NOW! Visit your local UF/IFAS Extension citrus agent to get your copy today!

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UF/IFAS

Citrus Magazine December 2025