Progressive Crop Consultant - July/August 2023

July / August 2023

Fungal Canker Diseases of Sweet Cherry

Average Daily Temperature in 2023 Has Been Lower: What Does it Mean for California Red Scale?

Phytophthora Diseases of Row Crops: A Review

September 27th - 28th

Learn more on pages 12 -13

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Photo courtesy F. Trouillas

Fungal Canker Diseases of Sweet Cherry

Average Daily Temperature in 2023 Has Been Lower: What Does it Mean for California Red Scale?

Phytophthora Diseases of Row Crops: A Review

PLANTALIFE for Crop Stress

Dial In Spray Coverage for Cost-Effective Spraying

Using Plant Nutrition and Biostimulant Products to Continue Citrus Production in HLB-Infected Trees.

The Dynamic Duo: Exploring the Synergy between Irrigation and Nutrient Management

4 14 28

PUBLISHER: Jason Scott

Email: jason@jcsmarketinginc.com

EDITOR: Taylor Chalstrom

ASSOCIATE EDITOR: Cecilia Parsons

Email: article@jcsmarketinginc.com

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Phone: 559.352.4456

Fax: 559.472.3113

Web: www.progressivecrop.com

CONTRIBUTING WRITERS & INDUSTRY SUPPORT

Sandipa Gautam Ph.D., UCCE Citrus IPM Advisor

Raquel Gomez Research Agronomist, CCA, AgroPlantae

Kelly Ivors Senior Plant Pathologist, Driscoll’s

Steven Koike Director/Plant Pathologist, TriCal Diagnostics

JW Lemons CCA, CPAg

Franz Niederholzer UCCE Farm Advisor, Colusa and Sutter/Yuba Counites

Florent Trouillas Plant Pathologist, UCCE

Scott Warr Commercial Manager, Digital Farming Yara

UC COOPERATIVE EXTENSION ADVISORY BOARD

Surendra Dara Director, North Willamette Research and Extension Center

Kevin Day UCCE Pomology Farm Advisor, Tulare and Kings Counties

Elizabeth Fichtner UCCE Farm Advisor, Kings and Tulare Counties

Katherine Jarvis-Shean UCCE Orchard Systems Advisor, Sacramento, Solano and Yolo Counties

Steven Koike Tri-Cal Diagnostics

Jhalendra Rijal UCCE Integrated Pest Management Advisor, Stanislaus County

Mohammad Yaghmour UCCE Area Orchard Systems Advisor, Kern County

The articles, research, industry updates, company profiles, and advertisements in this publication are the professional opinions of writers and advertisers. Progressive Crop Consultant does not assume any responsibility for the opinions given in the publication.

Fungal Canker Diseases of

Sweet Cherry Improving Disease Management Using An Integrated Approach

By FLORENT TROUILLAS | Plant Pathologist, UCCE

Fungal canker diseases of sweet cherry trees can be devastating to an orchard’s productivity and longevity and thus constitute a major threat to the cherry industry in California. Managing canker diseases has been challenging for growers as no control strategy alone suffices to manage these diseases. With funding from the California Cherry Board, the Trouillas Lab at UC Davis has worked during the past several years to improve management of canker diseases.

Anti-Stress

Main Fungal Canker Diseases of Sweet Cherry

Main fungal canker diseases of sweet cherry in California include Calosphaeria canker, Cytospora canker and Eutypa dieback, with Calosphaeria canker being the most widespread canker disease in the state. These diseases affect cherry trees in all cherry-producing areas worldwide, including Australia, Chile, France and Turkey. Canker diseases are caused by the plant-pathogenic fungi Calosphaeria pulchella, Eutypa lata and Cytospora sorbicola. These fungi infect and colonize the wood of cherry trees, killing branches, scaffolds and trunks, and causing important yield losses. Fungal cankers are to be distinguished from bacterial canker caused by the bacterium Pseudomonas syringae, which mostly affect the bark of cherry trees but also can lead to the killing of branches and entire trees.

Symptoms of Fungal Canker Diseases

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A canker in woody plants usually refers to a lesion produced in the bark of twigs and branches. However, most fungal canker diseases colonize both the bark and internal wood tissues causing canker rots or wood cankers that persist for years. The dead area can block water and nutrient transport thus causing the dieback of affected branches. Wood cankers typically consist of reddish-brown to dark-brown discoloration of xylem tissues and may vary in shape from wedgeshaped to round, or irregular. Typically, if you cut through a disease branch on a cherry tree, canker infection will appear as vascular (wood) discoloration (Figure 1), which indicates a disruption in the flow of water and nutrients through the tree vascular system. It is also common for canker diseases to produce gumming near the infected area.

Biology of Fungal Canker Diseases

Calosphaeria pulchella and Cytospora sorbicola commonly produce fruiting bodies in sweet cherry trees. These can be observed easily beneath the periderm of dead or infected branches after

Figure 1. A wood canker in a branch of cherry tree with the typical discoloration of xylem tissues (all photos courtesy F. Trouillas.)

Figure 2. Fungal fruiting bodies (perithecia) of Calosphaeria occurring in groups with long cylindrical necks below the bark and that emerged together at lenticel openings.

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peeling the external bark tissue with a knife. This method is a great way to diagnose canker diseases in the field. Calosphaeria pulchella produces fruiting bodies or perithecia occurring in groups with long cylindrical necks that emerged together through the bark at lenticel openings (Figure 2, see page 4). Spores of Calosphaeria pulchella are primarily dispersed via rain and wind and infect open wounds such as pruning wounds. Sprinkler irrigation that wets the tree trunks also can contribute to spore release in cherry orchards, particularly during summer months. Cytospora sorbicola can be recognized as it forms pinhead-sized pimples pushing through the bark of cherry trees (Figure 3). These pimples are the reproductive structures of Cytospora. Under humid conditions, masses of spores may ooze out of the fruiting bodies in long, brownish, coiled, thread-like spore tendrils. These spore masses are then rain-splashed to fresh pruning wounds and other openings where infections initiate. Perithecia (the reproductive structures) of Eutypa lata are rarely observed on cherry trees in California. These mostly form on riparian trees such as willow or ornamental tree such as oleander as well as in apricot trees and eventually grapevine. Eutypa canker disease is more common in the Northern San Joaquin and Sacramento valleys as well as in Contra Costa and San Benito counties, and rarely occurs south of Merced County. During rainfalls, spores of fungal canker pathogens are air-dispersed or rain-splashed onto fresh wounds such as fresh pruning wounds where they germinate and initiate infection. Fungal mycelium then colonizes the heartwood before expanding into the sapwood, causing wood discoloration and the typical canker.

Management of Canker Diseases

To best manage canker diseases, we propose an integrated, preventive approach that minimizes risks of infection of sweet cherry trees by fungal pathogens. This integrated approach involves disease avoidance and prevention, combining cultural, chemical and biological control practices. First, pruning should

be performed to avoid rain and when dry weather is predicted for at least two weeks. Pruning of sweet cherry trees may be done after harvest during late spring and summer when conditions are warm and dry and when no rain is forecasted. Canker pathogen populations will be at their lowest during this period and the risk for infection is reduced. However, spore release and infection of pruning wounds can occur during late spring if rain occurs and during summer if sprinkler irrigation that wets trees is used in the orchard.

Overall, cold winter temperatures are unfavorable to pruning wound infection by Calosphaeria, and winter pruning may be considered particularly in orchards and regions where Calosphaeria canker represent the main canker disease. Indeed, spores of Calosphaeria pulchella will not germinate at temperatures below 15 degrees C (60 degrees F), and pruning during cold winter period can prevent infection of pruning wounds by Calosphaeria pulchella. Infection of pruning wounds by Cytospora sorbicola can be avoided also by pruning sweet cherry trees in the coldest parts of winter when temperature is below 10 degrees C (50 degrees F). Winter pruning, however, generally will not prevent infection of cherry trees by Eutypa if rain is present at the time of pruning. So, winter pruning is best done during cold and dry weather conditions, with no rain in the forecast.

Because pruning wounds serve as the main entry sites for canker pathogens, these must be protected following pruning of trees, especially if pruning occurs during the wet winter and spring months or during summer in orchards that receive sprinkler irrigation that wet the trees. Water from rain and sprinkler irrigation combined with wind are important factors for aerial dissemination of canker pathogens. Our laboratory recently evaluated the efficacy of different compounds to protect pruning wounds from infection by canker pathogens.

Of the different fungicidal compounds tested, Topsin M (Thiophanate-methyl) and Quilt Xcel (Azoxystrobin + Propiconazole) performed best against Cy-

tospora and Eutypa pathogens of sweet cherry, allowing significant disease reduction. Biological, Trichoderma-based products (e.g. Vintec®, RootShield® Plus) provided significant protection of pruning wounds against all canker pathogens, and performed best at reducing infection by Calosphaeria pulchella Fungicide or biocontrol products should be applied immediately after pruning to avoid infection at pruning wounds.

When orchards are seriously infected with canker diseases and branch dieback occurs, remove diseased branches/ limbs at least 4 to 6 inches below any sign of wood discoloration. The pruning cut should be made into healthy wood to ensure that all the disease has been removed. Incomplete canker removal wastes time and money with little to no benefit in disease management. Dead branches left in the orchard or adjacent to living trees provide inoculum for further infection and should be removed and destroyed. It is also advised to regularly disinfect pruning shears, particularly after cutting through dead wood, using common sanitizers or a flaming torch. Note that wood grinding or wood chipping potentially could release an important number of spores in orchards that could infect pruning wounds. Accordingly, the grinding or chipping of dead cherry wood should be avoided until at least several weeks following pruning. Although burning

Figure 3. Fungal fruiting bodies of Cytospora pushing up the bark on a cherry branch and looking like “pimples” on the bark surface.

of cherry wood is restricted, it is often the best option to get rid of fruiting bodies from cherry canker pathogens that have developed on dead wood. Storing dead wood near orchards also will have no effect at reducing inoculum sources unless the wood is thoroughly covered and protected from rain and irrigation water.

Topping cherry trees to encourage new vegetative growth also has been linked to severe sunburn damage in cherry orchards. Branches with sunburn damage then become highly susceptible to both fungal and bacterial canker pathogens. Techniques that help limit sunburn in cherry trees are encouraged to avoid canker disease outbreak in orchards. These may include proper pruning and training to promote adequate branch and tree structures as well as whitewashing, which consist of applying white paint to the interior of scaffold branches to reflect light and reduce bark heating from exposition to direct sunlight.

Management of canker diseases of sweet cherry is difficult due to the diversity of canker pathogens affecting sweet cherry trees in California. However, disease management may be achieved when considering multiple factors linked to disease spread and infection timing. These include the weather and weather forecast at the time of pruning and irrigation practices in the orchards as well as the orchard location and history of canker diseases. An integrated approach that combines disease avoidance and prevention is critical to achieve best control as no curative practices are available. While pruning must be conducted outside of the high-risk periods for infection, it is strongly advised also to protect pruning wounds with a fungicide or biological control agents.

Disclaimer: Mentioning of any active ingredients or products is not an endorsement or recommendation. All chemicals must be applied following the chemical label, local and federal regulations. Please check with your pest control adviser to confirm rates and site-specific restrictions. The author is not liable for any damage from use or misuse.

Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com

Average Daily Temperature in 2023

Has

Been Lower:

What

Does

it Mean for California Red Scale?

By SANDIPA GAUTAM | Ph.D., UCCE Citrus IPM Advisor

California red scale (CRS) is an armored scale insect that affects all citrus varieties. It attacks all aerial parts of the tree including leaves, fruits, twigs and branches by sucking on plant tissue with its long filamentous stylet. Heavy infestations cause leaf yellowing and drop, dieback of twigs and occasional death of the infested tree. Heavily infested fruits with patches of California red scale may be downgraded in the packinghouse. For managing CRS, an integrated approach that combines mat-

ing disruption, insecticides and biological control using Aphytis melinus is used. Growers and PCAs have long relied on using pheromone cards for monitoring males and use of degree days to predict future events for making treatment decisions. Insecticide applications give the best results when the population is at the most susceptible stage (immatures) and is uniform.

In a normal year, monitoring for CRS begins on March 1. PCAs put out pher-

Figure 1. CRS female (overturned) showing crawlers. Crawlers move around looking for feeding spot, settle and spend life on the same spot (photo courtesy UC Statewide IPM Project.)

Figure. 3. Number of males collected in pheromone trap at LREC. Note first fliers started 4 weeks later and peaked 4 weeks later. Second generation fliers stared on week of June

in

2023. Expect ~3

delay in crawler in second generation crawler emergence.

Figure 2. CRS male adult (top) and CRS males on trap card (bottom) (photos courtesy UC Statewide IPM Project.)

Figure 3. Number of males collected in pheromone trap at LREC. Note first fliers started four weeks later and peaked four weeks later. Second-generation fliers stared on week of June 19 in 2023. Expect about three-week delay in crawler in second-generation crawler emergence.

omone cards and call a biofix when first males are caught on the trap (biofix is the first event in CRS seasonal cycle.) In 2023, we got many calls from PCAs that their traps were empty in March. Our observation at the Lindcove REC center was the same. First males were found on trap cards on the week of April 10 and common consensus for biofix day was April 11. This situation is true for major citrus growing counties in the San Joaquin Valley.

How Do Lower Temps Affect CRS and its Management?

Like all other insects, development of CRS is temperature dependent. Season starts with surviving overwintering females. As the temperature increases and heat units accumulate, gravid female produces crawlers (Figure 1, see page 8). Crawlers only remain mobile until they find a suitable location to begin feeding. Once they start feeding, they do not move and go through development being attached to the feeding spot. Crawlers go through active feeding stage (instars) and a dormant period (molting). Females molt twice and males molt four times and emerge as fliers. Males are the only other moving stage (Figure 2). Males find and mate with third instar females. Afterwards,

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gravid female starts producing crawlers, hence completing the life cycle. In the San Joaquin Valley, there are four complete generations of CRS. In years with warm winters/hot summers, partial fifth generation (immatures/males) have also been reported.

CRS does not develop below 53 degrees F, and it is the lower developmental threshold (LDT) temperature based on which degree days for CRS development are calculated. Using CIMIS station data for four counties (Kern, Tulare, Fresno and Madera), I calculated the cumulative degree days above the LDT for CRS since 2020. Figure 2 shows degree days in 2023 trails below those for years 2020-22. Effects of low average

daily temperature were first noticed when biofix was delayed by about four weeks in all four counties. Figure 2 (see page 8) shows number of males/trap at Lindcove REC station, where biofix and first-generation flight peak were about four weeks later than in 2022. Second-generation flight started on the week of June 19, which is also about four weeks delayed. This means CRS is developing, but at a slower rate than it had been in earlier years (Figures 2 and 3, see page 8). It takes 550-degree days after the male flight for crawler emergence. Expect second-generation crawler emergence, third-generation male flights and consequent generations to be delayed. Relatively cooler spring and early summer temperatures mean less heat units/day and delayed development, thereby affecting male flight and crawler emergence, which will in-turn

affect spray timing for CRS control in the 2023 season. Visit lrec.ucanr.edu/Citrus_IPM/Degree_Days/ for degree day updates in Kern, Tulare, Fresno and Madera counties.

Management Monitoring

Monitoring for California red scale and applying treatments to target the most susceptible life stage/generation is key to managing CRS. Goal is to maintain CRS populations at low levels to minimize fruit contamination at harvest. UC IPM guidelines has a list of updated recommendations.

Mating disruption

Mating disruption such as Checkmate CRS prevents or delays mating of males with females. Unmated females do not produce crawlers and stay as third instar females which is the preferred stage of parasitism by Aphytis melinus. Application of mating disruption (180/ acre) prior to the onset of first or second generation (March or May) have shown to provide best results (Grafton-Cardwell et al. 2021).

Biological control

Parasitic wasps Apytis melinus and Comperiella bifasciata are important natural enemies that help manage CRS. However, these parasitoids can be susceptible to insecticides used for other pests, so their effectiveness depends on careful monitoring and use of selective insecticides (UCIPM Guidelines 2022).

Insecticides

Several insecticides have proven efficacy against CRS (UCIPM Guidelines 2022, Grafton Cardwell 2016). However, a number of populations have developed resistance to organophosphates and carbamates. Field observations show resistance to pyriproxyfen may

Figure 4. Cumulative degree days above the lower developmental threshold, 53 degrees F, for CRS in Madera, Fresno, Tulare and Kern counties. Note that 2023 (black line) trails below other years.

Figure 5. Mean live CRS per fruit on October 12 counts following insecticide treatment. All treatments were applied with 1% oil.

have developed (UCIPM Guidelines 2022). Where resistance to carbamates or pyriproxyfen is suspected, use of alternate chemicals such as buprofezin, spirotetramat, mating disruption and release of Aphytis may provide better results (UCIPM Guidelines 2022).

California Red Scale Trial, 2022

A field trial to evaluate multiple insecticide treatments on California red scale was conducted at the Lindcove Research and Extension Center in 2022 (Gautam and Dhungana 2023). Treatments were randomly assigned to single-tree plots that were organized into blocks based on pretreatment counts of CRS/twig on 25 July, 2022. Treatments were applied on July 28 in 750 gallons of water, except for Movento which was applied in 250 GPA, and Centaur which was applied at 1,000 GPA. Post-treatment evaluation was done by rating twigs on September 23 and twigs and fruit on October 12 for the presence of live CRS. We also rated fruit for infestation by CRS, 0=no scale, 1=1-10 scale/s, 2= >10 scales/fruit. The insecticides applied were Movento at 10 oz, Sivanto at 14 oz, Centaur at 46 oz, Senstar at 20 oz and Esteem at 16 oz.

The insecticide that provided the best control in terms of reducing the percentage of fruit infested with >10 scales was Movento (Figure 5, see page 10). Treatments, namely Centaur, Senstar, Sivanto and Movento, significantly reduced the total CRS/fruit compared to control (Gautam and Dhungana 2022).

Treatments should be applied to provide thorough coverage according to the size of the trees, except for Movento which is recommended at 250 GPA. See UC IPM guidelines for CRS for more application details and recommendations.

References

Gautam SG, SK Dhungana. 2023. California red scale insecticide trial, 2022. https://doi.org/10.1093/amt/tsad067

Grafton-Cardwell, EE, JT Leonard, MP Daugherty, DH Headrick. 2021. Mating Disruption of the California Red Scale, Aonidiella aurantii (Hemiptera: Diaspididae) in Central California Citrus. 114:

2421-2429

Grafton-Cardwell, EE, SJ Scott, and JE Reger, 2016. California red scale insecticide efficacy trial, 2016. https://doi. org/10.1093/amt/tsx044

UCIPM guidelines 2022. Citrus Pest Management Guidelines: Selectivity of Insecticides and Miticides.

https://ipm.ucanr.edu/agriculture/citrus/

selectivity-of-insecticides-and-miticides/

UCIPM guidelines 2022. Citrus Pest Management Guidelines: California red scale and yellow scale. https://ipm.ucanr. edu/agriculture/citrus/california-redscale-and-yellow-scale/

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Phytophthora Diseases of Row Crops: A Review

By STEVEN KOIKE | Director/Plant Pathologist, TriCal Diagnostics and KELLY IVORS | Senior Plant Pathologist,

Phytophthora is the genus name given to a group of fungus-like organisms that have tremendous impacts on plants. Recent research indicates Phytophthora is closely related to brown algae and diatoms. Of the many documented Phytophthoras, a few dozen species cause disease on vegetable, fruit, ornamental and forest plants grown worldwide. Phytophthora has a notorious record for damaging crops. One of the earliest notable cases involved Phytophthora infestans, which caused epidemics of late blight on potato in Europe in the 1840s to 1850s. Devastating losses of potato crops resulted in famines, human suffering and death, and forced migrations. Another species, P. cinnamomi, caused the loss of hundreds of plant species in Australia. Such widespread decline threatens the plant and animal ecosystems in this region. And even closer to home, in coastal California and southern Oregon, P. ramorum (sudden oak death) has killed millions of tanoak and coast live oak trees, and imposed the destruction of millions of ornamental nursery plants due to state and federal regulatory measures. This article will focus on Phytophthora problems of annually grown row crops.

Types of Phytophthora Diseases

Phytophthora is a plant pathogen that resides in the soil. However, this soilborne

pathogen can cause both belowground and aboveground diseases.

Root and crown rot

The majority of Phytophthora diseases involve tissues in contact with infested soil (Table 1). Roots are directly infected by Phytophthora in the soil; such roots become gray, brown or black in color. Roots later decay, with outer layers of the root sloughing off, leaving intact only the central wiry xylem core. While the stems and crowns of annual crops can be directly infected by Phytophthora

present in the rhizosphere, it is common to have root infections progress up the root and into the crown. Diseased crown tissues likewise become discolored and decayed. More fibrous row crops like strawberry will also manifest discolored roots and crowns. However, these roots and crowns usually retain their structure and do not have the soft decay symptom.

crops having root and crown infections can appear delayed in development, stunted and deficient in nutrients

All

Table 1. Some Phytophthora species, primary diseases they cause, and plants they infect.

Driscoll’s

Phytophthora can rot both crowns and roots of row crops (two healthy shallot plants on left) (all photos by S. Koike.)

due to non-functional roots. With time, these plants wilt, collapse and die. Fruit-bearing row crops can develop a gray to brown rot on fruit if such fruits are in contact with soil or puddled water. Fruit diseases can be seen on cucumber, melon, squash, pepper, tomato and strawberry. Postharvest decay can occur if fruits are infected in the field prior to harvesting.

Foliar blights

Some Phytophthora species can produce airborne or splash-dispersed spores that can infect leaves, stems and fruit that are not touching the ground (Table 1, see page 14). Initial symptoms include small, brown or gray lesions. Such le sions rapidly expand to affect large areas of the foliage, causing it to collapse. Fruits can also be infected by these ae rial spores, resulting in fruit rot. Collec tively, such diseased foliage and fruit are called blights. As previously mentioned, one of the best known foliar Phytoph thora diseases is late blight of potato and tomato caused by P. infestans. Phytophthora capsici causes both root and crown rot diseases as well as foliar blights on cu-

curbits and other vegetables. While not formally called a “blight,” P. ramorum causes aboveground diseases on foliage, twigs, branches and trunks of many woody trees and shrubs.

Biology and Disease Development

Phytophthora species are labeled with the common name “water molds.” This is an appropriate name because these organisms are closely connected to water. If sufficient soil moisture is present, Phytophthora will grow mycelium like fungi.

If host roots and favorable soil water conditions are present, Phytophthora will produce asexual reproductive structures called sporangia. Sporangia are flask- or oval-shaped structures within which are made zoospores. Zoospores released from these sporangia will swim in the soil water in the direction corresponding to increasing gradients of root exudates, land on roots and initiate infections. Sporangia and zoospores are

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Crop resilience against disease and pest pressure can be achieved with a biological program and balanced nutrition.

Phytophthora on peppers and other vegetables can cause internal discoloration of the crown.

ContinuedfromPage15

short-lived structures; if a host root is not found or if soil conditions become too dry, these structures shrivel up and die.

In addition, Phytophthora forms a second type of structure that is spherical, with a thick resilient cell wall, that is called an oospore. Oospores are sexual structures that allow Phytophthora to recombine genetically and form diverse genotypes and strains. With their thick walls, oospores enable the pathogen to survive periods when the soil is dry and host plants are absent. Oospores are the likely means by which these pathogens are spread when contaminated soil is moved from field to field.

Detection and Diagnostics

Confirmation that Phytophthora is causing a disease requires laboratory testing. Traditional culturing methods, in which pieces of diseased plant tissue are placed into Petri dishes containing selective agar media, are still very useful. More advanced and rapid detection tools

include serological methods (such as lateral flow devices or ELISA) in which specifically designed antibodies detect the antigens of Phytophthora and molecular methods (such as qPCR or RPA) in which molecular markers target the Phytophthora DNA. In seeking confirmation of Phytophthora diseases, make sure the diagnostic lab has experience with Phytophthora and uses the appropriate tests.

Diagnostic precision is needed because several soilborne pathogens including Phytophthora cause similar symptoms on row crops. Plant pathogenic species of Pythium and Phytophthora in particular cause very similar root rots, crown infections, foliage yellowing, leaf

ContinuedonPage18

FIRST THING I’VE GOT TO DO IS SQUIRREL. AND THEN I’VE GOTTA SQUIRREL. AND AFTER SQUIRREL, I NEED TO SQUIRREL.

Table 2. Comparing symptoms caused by Phytophthora, Pythium, and vascular wilt pathogens

Managing Phytophthora Managing soilborne Phytophthora diseases uses strategies like those

Seedling damping-o

Root rot

Crown rot

Vascular discoloration

Foliar blight

Fruit rot

Chlorosis, nutrient de Wilting, leaf drop

General poor growth

Plant death

ContinuedfromPage17

wilting, poor overall growth and death of the plant (Table 2 vascular wilt pathogens such as and Verticillium symptoms that resemble Phytophthora root and crown diseases (

Have qualified professionals confirm is the issue; in some cases, it is useful to also know which

Choose fields that do not have a histoproblems and that have well-draining soils. Soils higher in clay content have been associated with

is a concern, avoid backto-back plantings of the same susceptible crop. Rotate with crops that are not Phytophpresent at that location. Selection

of non-susceptible crops will depend on the identification of the Phytophthora species (Table 1, see page 14).

Irrigation management

Because Phytophthora is dependent on wet soil conditions, carefully schedule irrigations to prevent over watered, saturated soils. Low-flow irrigation systems such as drip irrigation for strawberry and microsprinklers for tree crops, can help discourage Phytophthora outbreaks. When possible, route excess or ponding water away from the production area with the use of ditches, raised beds or slopes.

Sanitation

Sanitation refers to measures used to prevent the introduction or spread of the pathogen in the growing location. Because Phytophthora resides in soil, avoid moving mud-encrusted farm implements from infested areas to clean fields. Avoid using transplants, cuttings and other vegetatively propagated materials that show disease symptoms and are infected with Phytophthora.

Fungicides

For some crops, applying fungicides to the crop may provide some protection. Because Phytophthora is not a true fungus, fungicides with modes of action effective against oomycete diseases are necessary. The repeated use of products having the same mode of action can result in Phytophthora populations that are insensitive (=resistant) to those products; therefore, fungicide applications should include products having different modes of action.

Resistant or tolerant cultivars

There appear to be relatively few row crop cultivars that are genetically resistant to Phytophthora; on the other hand, some cultivars (e.g., the strawberry cultivar Radiance) are known for their increased susceptibility to Phytophthora diseases.

The IPM components for managing soilborne Phytophthora diseases are also relevant for foliar Phytophthora problems and include proper diagnosis, site selection, crop rotation and genetic resistance. For foliar Phytophthora, the

mode of irrigation can be extremely critical; the use of overhead sprinkler irrigation can exacerbate Phytophthora blights on cucurbits, tomato, potato and pepper, for example. Sanitation is a key factor for the prevention of epidemics of late blight since P. infestans can over-season on infected plant material. For example, diseased potato tubers, left in old fields or lying in cull piles near production areas, are a source of airborne spores that can infect new plantings. Managing foliar Phytophthora diseas-

es relies more heavily on protectant fungicide sprays than control programs targeting soilborne Phytophthoras. For this reason, careful field scouting plays a critical role for early detection of symptoms and deployment of fungicide tools.

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• supports crops under stressful conditions.

is synergic when it’s blended with, fungicides, phosphite, or foliar fertilizers.

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PLUS™ ADVERTORIAL

PLANTALIFE for Crop Stress

By RAQUEL GOMEZ | Research Agronomist, CCA,

The seemingly never-ending drought followed by unexpected and poorly timed rain in 2023 has highlighted the importance of incorporating practices intended to support and protect crops from all stressors. However, environmental stress is not the only stress affecting crop yields; physiological stress due to crop load can affect harvest quality and marketable yield. Plant sensitivity to heat stress can vary by crop, variety, heat duration and many other factors. Research has shown the importance of managing crop stress at all growth stages that include reproductive growth like bloom, fruit development and in perennial crops the period in which the following years buds are setting. There are tools to measure soil moisture or transpiration, and environmental parameters can be used to estimate irrigation needs to lessen heat and drought stress. However, stem water potential (SWP) is the only true parameter that measures the plant water status and can quantify specifically plants’ stress due to water needs. SWP measures water tension in plants by applying pressure to a cut leaf and stem enclosed within the chamber. The measurement results in a negative number. The more negative or closer to -100 bars, the more stress, and the more positive (closer to zero) indicate less stress. Most tree crops have thresholds for SWP, almonds included, such that categories of stress

Figure 1 Figure

AgroPlantae

Figure 2. Fruit BRIX development after treatment applications were made.

Figure

Figure 1. Stem water potential (bars) and daily Maximum Temperature in Fresno, Calif. in relation to PLANTALIFE application and measurements.

Capturing Maximum Genetic Potential

In a 2022 trial done in California’s Central Valley on mature Nonpareil almonds, PLANTALIFE was sprayed in anticipation of a six-day heat wave, where temperatures were going to remain above 104 degrees F for five days. A plant’s natural threshold for reduced transpiration and closure of stomata

than 10 days. On application day, SWP was similar between the treatments. As the heat and days progressed, separation was observed where PLANTALIFE trees were noticeably less stressed compared to GS. While this data only shows one instance, this phenomenon has been observed in multiple crops and multiple areas. When a crop is less stressed, it

can provide growers’ protection against unpredictable elements and differentiate their crop quality in the market.

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Figure 3. Fruit color development treated GS, Seaweed, PLANTALIFE+SEAWEED or PLANTALIFE alone.

Dial In Spray Coverage for Cost-Effective Spraying

By FRANZ

The goal of airblast spraying is a uniform pesticide deposition of a known, prescribed pesticide rate throughout the entire target (tree canopy). Done right the first time, a good spray job saves the time and money of a second spray plus income lost due to crop damage in the case of a poor first spray (in tough economic times, a second spray for the same problem may not be in the budget.)

There are several steps to achieving this goal. Skipping any step will reduce spray efficacy and efficiency.

Step 1: The sprayer should travel at an appropriate speed to allow spray to reach the treetops. Too slow sprayer speed wastes time, too fast means poor coverage in the treetops and the risk of income loss due to crop damage.

Step 2: Point larger nozzles at thicker canopy (more leaves and nuts). For most orchard crops, this means 65% to 80% of the spray flow (gallons per minute) should be applied through the top half of open nozzles.

Step 3: Measure gallons per acre sprayed and, using total spray tank volume, determine the amount of pesticide product to add to each tank, to match your PCA’s recommendation.

Details

Ground speed

Airblast spraying uses air from the sprayer’s fan(s) to move the pesticide throughout the tree. If the fan’s air doesn’t reach the treetops, the pesticide won’t either. Ground speed is a simple and effective way to adjust air movement through the canopy, especially between bloom and harvest when spray coverage is most challenging.

The sprayer should travel fast enough so air from the sprayer’s fan reaches up through the tree to just above the tops of the tallest trees. To check this, at a time of day with little to no wind, tie a short (18-inch) length of surveyor’s ribbon to a section of PVC pipe or conduit and run the tubing up through the middle of a tree to a height just above the tallest trees in a planting. With the sprayer fan “on,” drive the sprayer past the tree with the flagging at tractor and sprayer settings you think is appropriate (e.g., full sprayer air delivery and 2.25 MPH sprayer speed). If the flagging flutters out to 45 degrees from the vertical as the sprayer passes the tree, the speed is appropriate for that planting at that time of the season. If the flagging just barely moves or doesn’t move at all, repeat the process with

slower tractor speed. If the flagging kicks up to the vertical (180 degrees from dead hang), repeat the process at a faster tractor speed. Record the tractor and sprayer settings that deliver air movement from the sprayer fan to just above the canopy. Calculate the acres per minute sprayed at that ground speed by multiplying ground speed (feet per minute) by the row width. Note: If spraying on a day with slight winds, drive slower, delivering more fan air to compete with the wind and better cover the upper canopy.

Nozzle selection

With a gallons per acre (GPA) target from your PCA and the appropriate sprayer speed measured with the aforementioned “flagging on a pole” process, calculate the sprayer output (gallons sprayed per minute; GPM) needed.

Gallons per minute = (Gallons per acre) x (Acres per minute)

Now select nozzles to deliver the GPM you just calculated (on paper). More spray should be applied to areas of the tree with more leaf area. Upper-canopy locations often hold more crop than the rest of the tree and are the toughest to cover. Extra spray volume with larger nozzle size targeted there will deliver more uniform coverage.

Step 1: Park the sprayer in the orchard and

Step 4: Check coverage with water-sensitive paper (WSP) placed in the canopy.

NIEDERHOLZER | UCCE Farm Advisor, Colusa and Sutter/Yuba Counites

In mature orchards, 65% to 80% of the spray flow should be applied through the top half of open nozzles (all photos by F. Niederholzer.)

Tying flagging to the nozzle ports and running the fan can help show you which ports point where in the tree. If the fan’s air doesn’t reach the treetops, the pesticide won’t either.

look where the different nozzle ports are located. Tying flagging to the nozzle ports and running the fan can help show you which ports point where in the tree.

Step 2: Using the manufacturer’s catalog and desired system pressure (for example, 150 psi), select nozzle sizes to locate on different nozzle ports. The goal for mature trees is 65% to 80% of the total GPM going out the top half of the open nozzles. That is, if there are 16 nozzles per side of a sprayer that should be open in a particular orchard based on the sprayer and tree size, the top 8 should have most of the total GPM. Using the same nozzle size at every nozzle port will, at best, overspray the lower canopy while delivering good/decent coverage to the treetops (as long as the ground speed is right.)

Gallons per acre

With the ground speed and nozzles selected, determine the GPA by checking the math you just did in the previous step. Park the sprayer on flat ground and completely fill the tank with clean water. With the nozzles just selected on the sprayer and using the sprayer and tractor settings for the right/appropriate ground speed, turn on the spray booms for a measured amount of time (one minute, two minutes, etc.) and then shut off the flow. Refill the sprayer with clean water using calibrated buckets or a hose with a flow meter to measure how much water was sprayed in the time the nozzles were “on.” Calculate GPM from the volume sprayed and the run time. Adjust GPM, as needed, using the system pressure or by changing nozzle sizes or parts (e.g., twoor four-hole swirl plates for disc/core nozzles) to deliver the recommended GPA.

Check coverage

Water-sensitive papers (WSP) are small cards with yellow coating on one side that turn blue where water (or fingerprints) touches the surface. To check spray coverage, place WSP at different heights in the trees in the orchard. This can be done several ways. If you have a pruning tower, use it to get up into one or more trees in the orchard and directly clip WSP to leaves or attach to nuts. Flag each WSP location so you can find it later. Another method is to attach WSP at different heights on a PVC pole and run the pole up through the middle of the tree canopy. Once WSP are up in the canopy, spray clean water

down the row where WSP are placed using the tractor settings and nozzle selection/location determined earlier. Take down WSP after and compare upper- and lower-canopy locations to see if coverage is generally uniform. You can measure coverage with a smartphone camera and apps, but a visual scan should be enough. Are the lower cards all blue? If so, the lower canopy is getting too much spray. One possible fix for this is to change out lower nozzles for a size smaller and repeat the test. If the upper cards are not getting much coverage, increase selective nozzle sizes that target the upper canopy and/or slow down the sprayer.

Spraying when relative humidity is low (<40%) can cut spray deposition in the upper canopy in half compared to spraying when relative humidity is higher (early morning). This can lead to poor pest control and/or development of pesticide resistance. Especially in warm summer months with low daytime humidity, night and early morning spraying is important to achieving good spray coverage.

Effective pest control with pesticide(s) is a key backstop in a good, cost-effective IPM program. Good spray coverage (and material selection/spray timing) ensures the backstop is solid.

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Using Plant Nutrition and Biostimulant Products to Continue

Citrus Production in HLB-Infected Trees

By JW LEMONS |

Citrus huanglongbing (HLB), previously called citrus greening disease, has been covered in thousands of articles. New technology and management tools continue to be discovered. Yet we still have no definitive cure and it could be a while before we see one. New rootstocks are surfacing, and treatment techniques are having some effect on slowing this devastating disease that has destroyed huge amounts of the world’s citrus trees.

As a Certified Professional Agronomist and a Certified Crop Advisor, I must prepare myself for HLB and its arrival here in the rest of California. It is currently here in one county. Many qualified scientists are approaching this menace with specific technologies, genetic modifications to trees, finding new resistant root stocks and of course trying to find something that will destroy the infections as well as a chemical or biological spray or injection that can combat and even cure the infection.

Others are addressing the psyllid vector, Diaphorina citri, that spreads the disease. Spray timings, mating disruptions, netting to cover the trees and keep the insect off them are being addressed.

Nutrition for Management

One approach I have used over the years mainly in Florida and Texas is based on years of repeated trials. It calls for using balanced and adjusted plant nutrition. It is most certainly not a cure, but I have witnessed improved yield, tree health, fruit quality and additional years of production from infected trees. It takes management and a deep knowledge of your citrus trees. When are the critical

CCA, CPAg

Well balanced nutrition programs for citrus may improve yield, tree health, fruit quality and additional years of production in HLB-infected trees.

The concept of well-balanced plant nutrition in citrus.

times of a developing tree, flower, bud development and fruit set, sizing, brix production and even color?

We need to study the amounts and most effective types of nutrients to apply. Balancing your crop nutrition is always critical, but a crop infected with the HLB needs special attention and application changes from a healthy crop nutrition program. A well-balanced program may handle these demands.

We must do more than a normal citrus nutrient program. One should understand the beneficial use of foliar applications of fertilizer nutrients and SAR (Systemic Acquired Resistance) products to maintain the health of HLB-infected trees. Several groves have maintained tree health and production by producing 7 to 10 years of profitable crops. The cultural production programs consist of a foliar spray cocktail of nutrients and SAR products applied three or more times per year to coincide with the initiation of vegetative growth flushes. The

application of the nutrient/SAR foliage spray program can reduce and ameliorate HLB leaf symptoms and includes a good soil-applied dry fertilizer.

We know the movement of the bacteria inside the roots and leaves severely

blocks the phloem tissue of these two areas. The interruption and restrictions to the movement of nutrients and sugars results in leaves dropping and

The greatest gain in fruit retention can be made during fruit set.

remaining leaves being smaller. By using products that can stimulate or increase the efficiency of these affected areas, we should be able to improve movement of nutrients and sugars.

Research has shown that by applying potassium foliarly, we can improve the health and production of infected trees. Polyamines have also been shown to be effective.

Other Possibilities

If simply changing application methods and fertilizer sources can make major changes, we can start to imagine other possibilities.

Verdesian Life Science has proven the use of phosphites can improve sugar and size in citrus fruit when compared to citrus trees not using this technology. Phosphites also trigger a plant’s own ability to increase its SAR. Plants have this ability to help them fight off infections.

Verdesian also uses other proven biostimulant products such as Primacy Alpha that through foliar applications increase nitrogen assimilation. The increased effect on the glutamine/glutamate pathway increases production of amino acids, proteins, lipids and other essential building blocks in the plant. We have seen a consistent increase in new root growth. This could lead to a healthier pathway for water and nutrient uptake. Water uptake is essential to carry nutrients and provides much of the fruit weight.

With Primacy Alpha, we documented increased leaf size, chlorophyll production, and CO2 fixation which could offset the HLB effects on leaves. With the documented increased flowering, we might improve fruit counts. With consistent nitrogen uptake improvement along with whole plant biomass gains, we continue to successfully improve the health and production on healthy and stressed crops. Primacy Alpha also contains a cytokinin precursor. It trig-

Research showed potassium nitrate resulted in the highest net income increase, $1925/ha/ year in HLB-infected Florida citrus.

Potassium nitrate sprays show less greening in Valencia oranges.

Increased leaf size, chlorophyll production and CO2 fixation were documented in citrus trials using Primacy Alpha.

gers the plant to produce more natural cytokinin. Cytokinins play a role in cell division. More cells mean bigger fruit.

If plant growth, smaller fruit, leaf development, reduced chlorophyl production and activity plus phloem blockage are results of HLB, it stands to reason that stimulating and improving these restricted systems could benefit the affected crop.

Seeing the effect HLB has on fruit size and fruit color, we must seek ways to offset these things that reduce marketability of fruit.

Products such as Cyto-Red+, a unique blend of patented technologies, help support plant performance through chelation/complexation. MAC Trigger upregulates genes involved in the shikimic acid secondary metabolite pathway, which leads to production of flavonoids

and anthocyanins, which are the main color components of the fruits.

I could spend days and thousands of additional words and examples to show how using plant nutrition and biostimulant could help at least extend the quality production on HLB infected citrus.

It is not a cure but simply a temporary solution to continue producing fruit while we find a permanent solution.

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Solar Protectant & Heat Stress Solution

Eckosil Shield Cuticle Enhancer is a soluble Orthosilicic acid formulation specifically designed to alleviate crop abiotic & heat stress and sunburn. It helps to reinforce plant cell walls, creating stronger plants with greater tolerance toward abiotic stress, reduced sunburn potential, and improved light absorption which leads to greater crop quality and marketable yield.

Products such as Cyto-Red+, a unique blend of patented technologies, help support plant performance through chelation/complexation.

‘If plant growth, smaller fruit, leaf development, reduced chlorophyl production and activity plus phloem blockage are results of HLB... stimulating and improving these restricted systems could benefit the affected crop.’

The Dynamic Duo: Exploring the Synergy between Irrigation and Nutrient Management

By SCOTT WARR | Commercial Manager, Digital Farming, Yara

As agriculture faces increasing pressure to produce more food with less resources, the role of irrigation and nutrient management has become ever more critical. Efficient irrigation and nutrient management practices are essential not only for maximizing crop yield and quality, but also for promoting sustainability and minimizing environmental impacts. In this article, we will explore the interconnected role of irrigation and nutrient management in agriculture and how growers and advisors can implement strategies to improve their efficiency and effectiveness. By understanding the relationship between these two critical factors, we can promote sustainable agriculture while ensuring food security for generations to come.

Years ago, as I was interviewing many

farm managers and their advisors to better understand their irrigation practices, I kept hearing one common statement: “The fastest way to compromise a great nutrition plan is to irrigate improperly.” Efficient irrigation management is crucial to minimize water losses, optimize nutrient use efficiency, improve soil health and increase grower profitability. Their goal is to manage irrigation by applying it at the proper time and rate for the specific crop demand and soil conditions. Excessive watering can cause waterlogging, nutrient leaching, soil erosion, disease and decreased crop yields. Conversely, insufficient watering can result in stunted growth and reduced harvest.

Agronomists have accepted and are committed to the 4Rs of Nutrient Management. While traditionally our 4Rs

focus has been on the nutrients delivered with fertilizers, we can use the same paradigm to manage the equally essential, and in some crop systems more limiting, nutrients of hydrogen and oxygen delivered in the form of H2O.

Right Source

Choosing the right source of water for irrigation is crucial. Water quality can vary significantly, and it is essential to consider factors such as salinity, alkalinity and potential contaminants. Testing the water source and ensuring it meets the required quality standards will help prevent adverse effects on soil health and plant growth. Growers and advisors should consider the following factors regarding water quality:

Salinity

High salt concentration can harm plants,

The same paradigm of nutrient management can be used for irrigation management when thinking about right source, right place, right time and right rate. Efficient irrigation management is crucial to optimize nutrient use efficiency.

reduce crop yield and quality, and affect soil health. Use electrical conductivity (EC) or total dissolved solids (TDS) meters to measure salinity and manage it through leaching, salt-tolerant crops or water treatment.

pH

Water acidity or alkalinity affects nutrient availability, uptake and soil health. Maintain a pH range of 6.0 to 7.5 through pH-adjusting chemicals or selecting pH-tolerant crops

Nutrient content

Nitrogen, phosphorus, and potassium levels in water impact plant growth and nutrient management. Adjust fertilizer rates or choose crops suitable for specific nutrient levels.

Pathogens and contaminants

Water may contain harmful bacteria, viruses and heavy metals that affect plant and human health. Implement water treatment, testing and monitoring practices.

Water availability

Consider the source, quantity and timing of water for irrigation. Implement water management practices to ensure availability throughout the growing season.

Water quality is vital for agricultural irrigation. Though growers cannot control the quality of their water source, they can monitor and adjust it as needed. Consider all relevant factors to ensure suitable water for crop growth without posing risks to plants or human health.

Right Place

The “right place” in irrigation management involves effectively delivering water and nutrients to the plant’s effective root zone. Advancements in irrigation systems, such as drip, micro and pivot systems, have improved water distribution and incorporated fertigation (applying fertilizers through irrigation.) Fertigation increases nutrient efficiency, reduces waste and promotes soil health. Regular maintenance ensures high dis-

tribution uniformity, avoiding uneven irrigation. To evaluate distribution uniformity, contact your local Natural Resources Conservation Department or refer to this resource: ucanr.edu/ sites/farmwaterquality/files/156399.pdf. Proper installation, maintenance and monitoring optimize the right place for uniform water and nutrient distribution, maximizing crop yield and sustainability.

Right Time

Knowing how much and when to turn on irrigation is crucial for maximizing water efficiency, promoting healthy plant growth, and optimizing crop yield. Consider the following factors:

Crop water needs

Understand the specific water requirements of each crop, considering different growth stages and their corresponding water demands. This knowledge helps

determine when irrigation is necessary for optimal crop development.

Soil moisture monitoring

Regularly monitor soil moisture levels using sensors or visual inspection techniques. This information identifies when the soil has dried sufficiently to require irrigation, avoiding both overirrigation and underirrigation.

Weather conditions

Monitor weather forecasts and local climatic patterns. Factors like temperature, humidity, wind and solar radiation influence evapotranspiration rates, affecting water loss from the soil and plants. Adjust irrigation timing based on anticipated water loss.

Plant stress indicators

vents water stress, promotes optimal plant growth and minimizes crop yield losses.

al-time monitoring of plant stress levels. Adjust irrigation timing based on these insights, improving water efficiency and

Advancements in irrigation systems, such as drip, micro and pivot systems, have improved water distribution and incorporated fertigation (photo by Taylor Chalstrom.)

ture-based scheduling, crop evapotranspiration (ET) data or plant water demand. These tools guide when to irrigate, considering crop needs and environmental conditions.

Water conservation considerations

In water-limited regions, time irrigation to maximize water use efficiency. Avoid peak water demand periods, applying water during cooler, less evaporative periods to minimize water loss and optimize utilization.

By considering these factors, growers can determine the appropriate timing for irrigation, ensuring crops receive adequate water when needed the most. This approach maximizes water efficiency, conserves resources and promotes healthy plant growth and optimal crop yield.

Right Rate

Once we know the amount of water the plant needs and when, we need to determine how frequently and how long to apply the water so that we do not have runoff or infiltration below the effective root zone. This might be an area for most improvement. By determining the appropriate rate, we can ensure that water and nutrients remain within the effective root zone, where plants can efficiently utilize them. This minimizes leaching and evaporation, reducing loss and waste.

To determine the right rate of irrigation:

• Understand soil characteristics, including type, infiltration rate and water holding capacity

• Determine the irrigation application rate specific to your system

• Consider the water demand of the crop

Several tools can aid in developing an effective irrigation schedule. These include evapotranspiration models, soil moisture monitoring and plant-based sensors that track water and nutrient uptake. By utilizing these approaches, farmers can align irrigation events with actual plant and soil water needs, maximizing water use efficiency.

As agriculture strives to meet the growing global food demand while conserving resources, the proper management of irrigation and nutrients has emerged as a critical aspect. This article has emphasized the importance of efficient irrigation and nutrient management practices for achieving optimal crop production, maintaining high-quality harvests and reducing environmental harm. By adopting the 4Rs of Irrigation Management that improve the efficiency and efficacy of these practices,

growers and advisors can contribute to sustainable agriculture. Through a comprehensive understanding of the interplay between irrigation and nutrient management, we can pave the way for a future where agriculture meets the needs of the present while safeguarding the needs of future generations.

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