Progresive Crop Consultant - September/October 2023

September / October 2023 Groundwater Banking on California Croplands New Instances of Herbicide Resistance in California Small Grain Crops Biostimulants and the Role of Cytokinin in Crop Performance

September 27th - 28th

Volume 8: Issue 5

Photo courtesy K. Van Leuven

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Progressive Crop Consultant September / October 2023

PUBLISHER: Jason Scott Email: jason@jcsmarketinginc.com EDITOR: Taylor Chalstrom ASSOCIATE EDITOR: Cecilia Parsons Email: article@jcsmarketinginc.com PRODUCTION: design@jcsmarketinginc.com Phone: 559.352.4456 Fax: 559.472.3113 Web: www.progressivecrop.com

IN THIS ISSUE

6 Groundwater Banking on California Croplands

CONTRIBUTING WRITERS & INDUSTRY SUPPORT

12 16 24

New Instances of Herbicide Resistance in California Small Grain Crops

Biostimulants and the Role of Cytokinin in Crop Performance

Sandipa Gautam Ph.D., UCCE Citrus IPM Advisor Nick Clark UCCE Agronomy Advisor, Kings, Tulare and Fresno counties

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Daniel Geisseler UCCE Nutrient Management Specialist Sudan Gyawaly UCCE IPM Advisor, Northern Sacramento Valley

Do Wider Beds in Fresh Market Onion Production Increase Total Water Productivity?

Orangeworm 2 8 Navel Hullsplit Spray

Considerations in 2023

Jairo Diaz Director, UC ANR Desert Research and Education Center

Philippe Rolshausen Ph.D., Professor of Cooperative Extension, Department of Botany and Plant Sciences, UC Riverside

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for Managing Vine 3 2 Tips Nutrition in Vineyards

Biopesticide Discovery

Roberto Soto Faculty Member, Universidad Autonoma de Baja California Tian Tian UCCE Viticulture Farm Advisor, Kern County Jennifer Valdez-Herrera Graduate Student Researcher, UC Davis Kirk Van Leuven PCA, CCA Katherine Waselkov Ph.D., Professor, California State University, Fresno Eryn Wingate CCA, Board Member, Western Region Certified Crop Advisers

UC COOPERATIVE EXTENSION ADVISORY BOARD Steven Koike Surendra Dara Tri-Cal Diagnostics Director, North Willamette Research and Extension Center Jhalendra Rijal UCCE Integrated Pest Kevin Day UCCE Pomology Farm Advisor, Management Advisor, Stanislaus County Tulare and Kings Counties Elizabeth Fichtner UCCE Farm Advisor, Kings and Tulare Counties

and 36 Challenges Prospects for

Anil Shrestha Ph.D., Professor, California State University, Fresno

Mohammad Yaghmour UCCE Area Orchard Systems Advisor, Kern County

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

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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.

September / October 2023 www.progressivecrop.com

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Wednesday, September 27

Thursday, Thursday,September September2828

7:00 AM BREAKFAST & TRADE SHOW

7:00 AM BREAKFAST & TRADE SHOW

JOINT DPR & CCA TRACK 8:00 AM Neighborly NOW Program: Getting Connected with Mating Disruption Users

JOINT DPR & CCA TRACK 8:00 AM Biostimulant Panel: Plant Biostimulant Act Reintroduction

Jesse Roseman, Principal Analyst, Almond Board of California

Russell Taylor, Vice President, Live Earth Products; Kirk Van Leuven, CCA/PCA, Stoller USA; Rich Kreps, CCA, SSp., Ultra Gro; August York, CCA, Intuit Ag Consulting; James Henderson, CCA, President, Prime Dirt, Inc.

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Renee Pinel, President/CEO, Western Plant Health Association; Surendra Dara, NWREC Director and Professor, Oregon State University; Roger Isom, President, WAPA; Daniel Hartwig, Director of Sustainability, Woolf Farming

Doug Snyder, Business and Marketing Development Manager, SQM North America

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Almond Carbon Footprint and Soil Health

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Tom Turini, UCCE Vegetable Crops Farm Advisor, Fresno County

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Jessica Chiartas, Ph.D., California Soil Resource Lab, UC Davis

Devin Clarke, Permanent Crop Manager, Yara International

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Nutrition and Soil Health Panel

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9:30 AM Industry Talk: Iodine as a Plant Nutrient

David Haviland, UCCE Area IPM Advisor, Kern County

Eryn Wingate, Agronomist, Tri-Tech Ag Products

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Sandipa Gautam, UCCE Area Citrus IPM Advisor, Tulare County

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Zheng Wang, UCCE Vegetable Crops and Irrigation Advisor, Stanislaus County

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4:30 PM Soil pH Nutrient Availability Table: Where did it come from and how to use it?

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5

Groundwater Banking on California Croplands

By ERYN WINGATE | CCA, Board Member, Western Region Certified Crop Advisers

On-farm groundwater recharge methods include winter flooding, skipped row flooding, subsurface reverse tile drainage, recharge ponds and unlined canals or irrigation ditches (photo courtesy Almond Board of California.)

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alifornia relies heavily on groundwater, with 40% of annual demand supplied by aquifers during non-drought years and upwards of 60% during dry years. Approximately 83% of people in California receive part of their annual supply from groundwater, and many communities are exclusively reliant on well water for both ag and domestic purposes3. Chronic groundwater overdraft, estimated at 2 million acre-feet per year since the 1960s, leaves California communities and farmland vulnerable to water shortages and rising surface water and pumping costs1.

Groundwater depletion also causes subsidence, or land sinkage, as dry aquifers collapse. Subsidence damages infrastructure, such as roads, powerlines, pipes and canals. The California Aqueduct’s flow capacity has reduced due to increasing subsidence rates, with some areas surrounding the infrastructure sinking almost 1.25 inches per month4. Groundwater recharge efforts have begun to reverse subsidence in some regions, but aquifer degradation and sunken land is often irreversible, and recharge efforts fail. The collapsed aquifers are irreparably damaged and can no longer store water.

California experienced the worst drought on record from 2012 to 2015, 6

exacerbating groundwater pumping overdraft, water shortages and subsidence. Recharge during rainy years does not replenish the loss, and between 2010 and 2020, roughly 28% of monitored wells in California declined by 5 to 25 feet3,6,8. State officials responded by passing the Sustainable Groundwater Management Act (SGMA) in 2014 to bring pumping and recharge into balance by 2040. Local groundwater sustainability agencies, tasked with developing recharge implementation plans, will likely include Agricultural Managed Aquifer Recharge (AgMAR) to meet requirements and balance the groundwater pumping budget7.

On-farm groundwater recharge methods include winter flooding, skipped row flooding, subsurface reverse tile drainage, recharge ponds and unlined canals or irrigation ditches. Traditional recharge methods like drainage basins require land dedicated solely to water percolation, limiting groundwater banking with high infrastructure construction costs and spatial constraints.

Winter surface flooding on irrigated agricultural land can be implemented widely at low cost and with few infrastructure or management changes at the field level. With 5 million acres of California farmland suitable for AgMAR, groundwater banking can scale

Progressive Crop Consultant September / October 2023

up dramatically if even a small percentage of acreage can dually purpose for recharge during rainy years3,6.

University research and early commercial implementation on orchards, vineyards and other crops indicate AgMAR can effectively recharge aquifers and benefit production in multiple ways3,5,6,7.

AgMAR helps growers and landowners secure irrigation water availability for dry years while preventing further aquifer degradation and subsidence. When properly managed, recharge efforts can also improve soil quality by leaching excess salinity below the root zone. Well water quality also improves when clean stormwater dilutes nitrate and total dissolved solids (TDS) accumulated in the basin after years of ag chemical leaching and pumping overdraft. Better soil and irrigation water quality improve crop health and fertilizer use efficiency, leading to lower production costs or increased yield and crop quality.

Implementation

Growers and landowners implementing AgMAR must consider soil suitability for recharge, crop tolerance, water application timing and field management practices to protect both crop health and groundwater quality. Research and field studies conducted over the

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September / October 2023 www.progressivecrop.com

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Recharge methods from left to right: surface application to orchards, subsurface application to orchards and basins/water conveyance structures (illustrations by Jennifer Natali, courtesy Almond Board of California.)

Continued from Page 6 last 10 years can guide site selection and implementation, but land managers must evaluate their own soils and crops to adjust AgMAR protocols to fit the unique conditions at each ranch.

Site Selection

The Soil Agricultural Groundwater Banking Index (SAGBI), developed

by Toby ‘O Geen and collaborators at UC Davis, provides a scoring system to determine farmland’s suitability for AgMAR6. SAGBI assigns scores in five categories, including deep percolation, root zone residence time, topography, chemical limitations and soil surface

condition. The weighted average of scores in all categories is used to classify ag land as Excellent, Good, Moderately Good, Moderately Poor, Poor or Very Poor for agricultural groundwater banking. The best ground for recharge is on flat land with sandy or sandy loam soils.

Ideally, the soil should have fast water penetration and infiltration, and little to no chemical limitations such as high salinity, nitrates or pesticide residue that could contaminate groundwater if leached into the basin6,8.

Over 17.5 million acres of farmland in California have been scored using data from the USDA-NRCS Soil Survey Database, and 5 million acres were rated as

Areas of soil suitability for groundwater banking in California taken from UC Davis web-based application. The application uses the Soil Agricultural Groundwater Banking Index to score specific farmland suitability.

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Progressive Crop Consultant September / October 2023

Excellent, Good or Moderately Good for AgMAR. Most of the land suitable for recharge is found in the eastern Central Valley as well as some locations in Santa Maria, Salinas and Napa6.

Land managers can look up their ground’s SAGBI score on UC Davis’ web-based mapping app at casoilresource.lawr.ucdavis.edu/sagbi/. Recharge suitability indicated by SAGBI scores should be verified on the field level by soil testing and site evaluation prior to AgMAR implementation.

Crop Suitability

Crop suitability for AgMAR depends on tolerance to soil saturation, crop value and financial risk, and likelihood of nitrate leaching due to typical fertilization patterns. Groundwater banking on agricultural lands is safest during winter dormancy or when fields are fallow. Surface applications typically flood the field with 6 to 8 inches of water that drains in a week or less depending on soil permeability2,3,5. Oxygen levels in the soil decline due to standing water, and if saturation persists for too long, the crop’s roots may be harmed.

Stressed and damaged root systems cannot absorb water and nutrients effectively, resulting in yield decline later in the season. Damaged roots are also more vulnerable to soilborne diseases such as phytophthora and fusarium, so fields with known disease pressure may not be good candidates for recharge5,7.

Growers can avoid root damage and

even improve soil health by choosing appropriate fields and planning surface application to match soil drainage rates and crop tolerance thresholds.

Crops suitable for AgMAR include alfalfa, wine grapes, tomatoes, almonds and other tree nuts. Annual cropping fields can also be used for recharge during the fallow period between plantings. Alfalfa presents a good candidate for recharge because its relatively low value poses less financial risk compared with specialty crops if recharge damages production.

AgMAR field experiments with alfalfa found no decline in root health or yield after winter flooding on well-draining soils, demonstrating growers can safely carry out recharge programs if the crop is in its dormant stage. Since alfalfa is sensitive to soil saturation during the growing season, researchers suggest rotating recharge sites to older crops scheduled for replanting the following year, especially if flooding events are expected in late winter or early spring3,7.

Trees and vines are excellent candidates for groundwater banking, if flooded during winter dormancy, well before budbreak. Crop sensitivity to water logging varies with rootstock, but growers are advised to limit standing water duration to two days to avoid root damage. Wine grapes are fairly tolerant to soil saturation, and since they typically receive less nitrogen fertilizer than other crops, residual nitrate levels during the winter are low. Tomatoes, almonds and other tree nuts generally receive higher nitrogen application rates, posing greater risk to groundwater quality if excess nitrate leaches during flooding events. Low nitrate levels and saturation tolerance position vineyards as the safest crop candidate for recharge, but groundwater banking will be more effective if implemented on the state’s vast almond acreage as well5,8.

UC Davis research funded in part by the California Almond Board demonstrated AgMAR efficacy on two commercial almond orchards in the Central Valley from 2015 to 20175. Researchers applied a total of 24 inches of water per year, split into multiple flooding

events during winter dormancy for two consecutive years. One of the orchards, located near Dehli, Calif., has highly permeable, sandy soil. The second orchard, located in Modesto, has moderately permeable, sandy loam soil. Flood water at both locations percolated below the root zone in less than a week, and researchers found no negative impacts on tree water status, root health or yield at either site. Winter flooding proved an efficient recharge method, with over 90% of applied water percolating below the root zone on the sandy soil

and over 80% percolation on the sandy loam. Similar studies on pistachios, wine grapes and tomatoes also resulted in effective groundwater banking while maintaining root health and productivity2,3,5.

California almond growers have begun implementing AgMAR on their own orchards with promising results. Mark McKean, a prominent grower in the Fresno area, began testing flood irriga-

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Continued from Page 9 tion and recharge in 2010, and by 2020 he had experimented with groundwater banking on 350 acres. In 2016, McKean banked 2 ac-ft/ac and in 2019 1.4 ac-ft/ ac on a three-year-old almond orchard.

McKean found better percolation when flood water was applied for short durations rather than one long set, and he reduces his fall nitrogen application rate on fields slated for winter recharge to prevent excess nitrate leaching below the root zone7.

Other growers have installed subsurface groundwater banking systems to pump recharge water below the root zone and bypass the risk posed by surface flooding. Diverted stormwater or other source water is piped down to a reverse tile drain system at least 8 feet below the soil surface. Several subsurface systems have been installed in the Central Valley since they were introduced in 2017, and some water districts offer incentives programs to help cover the costs. Subsurface recharge systems are expensive to install, but they facilitate high recharge volumes without impacting roots and crop health7.

Water Quality Considerations

Groundwater banking on ag lands has the potential to significantly improve water resource security in California, but AgMAR poses a risk to groundwater quality if excess salts, nitrates and other residual contaminants are leached down to aquifers. Preliminary soil testing can assess field suitability for recharge

When properly managed, recharge efforts can also improve soil quality by leaching excess salinity below the root zone (photo courtesy Almond Board of California.)

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before each rainy season, and sites with excess nitrate, salinity or pesticide residue may be passed up in favor of sites with optimum chemical characteristics.

Fields with higher residual contamination may still be good candidates for recharge if enough clean stormwater is available to dilute nitrate and salinity down to safe drinking water quality standards. Growers can also prepare for winter recharge by reducing the proportion of annual nitrogen fertilizer applied in the fall.

Residual contaminants in the vadose zone, the unsaturated area between the soil and the groundwater table, may also pose a risk to groundwater quality. Salts, nitrate and ag chemicals accumulated in the vadose zone after years of commercial agriculture may be mobilized by high-volume recharge events and leach down to the groundwater basin.

Hannah Waterhouse and colleagues at UC Davis analyzed soil core data down to 30 feet on 12 fields in the Kings groundwater basin to quantify potential risk of nitrate and salt contamination to aquifers8. The study compared the effects of soil permeability, crop type and fertilizer management on nitrate and salt accumulation in topsoil and below. Fields with lower water infiltration rates had higher nitrate and salinity levels compared with more permeable ground. Soils with slower water infiltration rates stored on average 732 lbs N/ac while lighter, well-draining soils stored 542 lbs N/ac within the 30-foot profile8.

Information gleaned from this study and other research can help determine the source and volume of water required for recharge at each site to ensure that leached contaminants are sufficiently diluted to protect well water quality.

Crop type and grower management also strongly affected nitrate and salinity levels. High nitrogen application rates on tomatoes and almonds were reflected in the soil profile, while wine grapes with lower N applications and deep root systems almost always contained the lowest nitrate levels. Elevated residual nitrate found on one outlier vineyard was explained by the grower’s fertilizer management. While other wine grapes

Progressive Crop Consultant September / October 2023

received split N applications, the field with unusually high residual nitrate received the entire year’s N supply in one shot at the beginning of the season, demonstrating management’s strong impact on nitrate leaching8. Regardless of crop type, growers implementing AgMAR can protect underlying groundwater by testing the soil’s N level in fall and adjusting fertilizer management to prevent nitrate leaching.

Groundwater quality monitoring and collaboration between growers, researchers and water agencies will help to safely implement AgMAR and improve recommendations to meet differing requirements at each ranch. Further research is required to understand how the vadose zone’s characteristics will impact groundwater quality in response to AgMAR, but initial studies indicate that the benefits of recharging our groundwater basins outweigh the potential risks when appropriate sites and field management strategies are implemented.

Average groundwater overdraft in California is estimated at about 2 million acre-feet per year, and from 2005 to 2010, the Central Valley alone overdrafted an estimated 1.1 to 2.6 million acrefeet1,6. Pumping restrictions required by SGMA may cause between 750,000 and 1 million acres of agricultural lands to go fallow without new supply mitigation measures7. Agricultural lands rated as Excellent or Good by SAGBI can percolate an estimated 1 foot of water per day, and if AgMAR were implemented on suitable wine grape acreage in the Central Valley, growers could bank 460 million acre-feet of water per day6,8.

AgMAR implementation at scale will require supply rights and infrastructure to divert excess stormwater to agricultural fields, but SGMA funding and compliance deadlines will likely motivate stakeholders to facilitate on-farm groundwater recharge efforts. Thousands of acres of wine grapes, almonds, alfalfa and tomatoes are planted on land suitable for groundwater banking, giving growers an opportunity to secure water resources for future crop production and their communities.

5. Ma X, Dahlke H, Duncan R, Doll D, Martinez P, Lampinen B, Volder A. 2022. Winter flooding recharges groundwater in almond orchards with limited effects on root dynamics and yield. Calif Agr 76(2):70-76. https://doi. org/10.3733/ca.2022a0008.

6. O’Geen AT, Saal M, Dahlke H, et al. 2015. Soil suitability index identifies potential areas for groundwater banking on agricultural lands. Calif Agr 69:75– 84. https://doi.org/10.3733/ ca.v069n02p75

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

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4. Lopes et al. 2017. California Aqueduct Subsidence Study. California Department of Water Resources, Division of Engineering, San Luis and San Joaquin Field Divisions. https://water.ca.gov/-/ media/DWR-Website/Web-Pages/Programs/Engineering-And-Construction/ Files/Subsidence/Aqueduct_Subsidence_ Study-Accessibility_Compatibility.pdf

8. Waterhouse H, Bachand S, Mountjoy D, Choperena J, Bachand P, Dahlke H, Horwath W. 2020. Agricultural

2,376.2 2,552.2

3. Dahlke H, LaHue G, Mautner M, Murphy N, Patterson N, Waterhouse H, Yang F, Foglia L. 2018. Chapter Eight - Managed Aquifer Recharge as a Tool to Enhance Sustainable Groundwater Management in California: Examples From Field and Modeling Studies.

Editor(s): Jan Friesen, Leonor Rodríguez-Sinobas. Advances in Chemical Pollution, Environmental Management and Protection. Elsevier, Volume 3: 215-275. ISSN 2468-9289. ISBN 9780128142998. https://doi.org/10.1016/ bs.apmp.2018.07.003.

managed aquifer recharge — water quality factors to consider. Calif Agr 74(3):144-154. https://doi.org/10.3733/ ca.2020a0020.

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2. Levintal E, Kniffin M, Ganot Y, Marwaha N, Murphy N, Dahlke H (2022): Agricultural managed aquifer recharge (Ag-MAR)—a method for sustainable groundwater management: A review, Critical Reviews in Environmental Science and Technology, DOI: 10.1080/10643389.2022.2050160

7. Roseman J, Lee E, Asgil L, Mountjoy D. 2021. Almond Board of California, Document #2021R0060. https://www. almonds.com/sites/default/files/2021-12/ WO-6177_ABC_GroundwaterRecharge_ Web_SinglePage.pdf

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References

1. [CDWR]California Department of Water Resources. 2009. Bulletin 160–09: California water plan update. Sacramento (CA): California Department of Water Resources. http://www.waterplan. water. ca.gov/cwpu2009/.

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New Instances of Herbicide Resistance in California Small Grain Crops Figure 1. Herbicide-resistant common chickweed grows unscathed to the top of the triticale canopy in this field after it was treated with ALS inhibitor herbicide (all photos by N. Clark.)

By NICK CLARK | UCCE Agronomy Advisor, Kings, Tulare and Fresno counties, ANIL SHRESTHA | Ph.D., Professor, California State University, Fresno, JENNIFER VALDEZ-HERRERA | Graduate Student Researcher, UC Davis, and KATHERINE WASELKOV | Ph.D., Professor, California State University, Fresno

S

mall grain cereals (wheat, triticale, rye, oats and barley) are planted each year in California on about 550,000 acres from the northern border near Oregon to the southern border near Mexico.

These versatile crops can be harvested as grain, straw, hay, green-chop or silage.

Today, much of the small grain cereals grown in California are used for dairy cattle feed. Dairy sales topped $7.6 billion in 2021, 14.8% of the state’s crop cash receipts.

Crop yield and quality reduction from weeds is a major concern of small grain producers. From 2015-19, PCAs recommended herbicides on an average of 941,000 small grain acres/year. Many fields were treated more than once for Figure 2. Early results from a replicated field trial could not rule out the possibility of ALS weed control (de Souza Dias et al. 2021). inhibitor herbicide genetic resistance in common chickweed found in triticale in the southern During this period, the most common San Joaquin Valley. “UTC” means “untreated control.” Skinny bars represent one standard herbicide modes of action on applied deviation. Treatments under similar lowercase letters are not significantly different from acres were acetolactate synthase (ALS) each other according to Tukey’s HSD test (a= 0.05). inhibitors (37.8%), synthetic auxins (31.8%) and protoporphyrinogen oxidase (PPO) inhibitors (17.7%). Major concernto control common chickweed (escapes) as mistakes in applications or poor ing weeds in California small grain crops several years in a row. Some fields were environmental conditions, several UCCE include littleseed canarygrass (Phalaris becoming overgrown with the weed Farm Advisors gave more attention to minor), Italian ryegrass (Lolium multiflorum), (Figure 1). fields with escapes and conducted early shepherd’s-purse (Capsella bursa-pastoris), evaluations attempting to repeat results London rocket (Sisymbrium irio), mustards An Emerging Problem PCAs and product reps saw in their trials.

(Brassica spp.), little mallow/cheeseweed As PCAs and pesticide product repre(Malva parviflora), coast fiddleneck (Amsinsentatives noticed some ALS inhibitor The PCAs were concerned they were ckia menziesii var. intermedia), burning netherbicides weren’t working as well as exseeing effects of herbicide resistance. tle (Urtica urens) and common chickweed pected to control common chickweed in This is a genetic phenomenon occurring (Stelleria media). small grains, they conducted field trials naturally as weeds are challenged to live and reached out to UCCE Farm Advisors when exposed to herbicides. Genetic In 2021, concerns from PCAs in the Nick Clark and Jose Dias and Specialist variation in the weed population gives southern San Joaquin Valley became urBrand Hanson. In 2021 when it was too gent as they noticed a pattern of failures difficult to dismiss the repeated escapes Continued on Page 14 12

Progressive Crop Consultant September / October 2023

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Continued from Page 12 some individuals natural resistance to the damaging effects of the herbicide. The problem arises when the same herbicide is used repeatedly, and those naturally resistant individuals continue to reproduce and become dominant in the weed population.

The diligence of these PCAs is the reason the broader ag community alerted early to this potentially serious problem.

Early Warning Grows into Full-Blown Research

Early testing in a field with high common Figure 3. Fresno State Masters student Jennifer Valdez-Herrera (right) teaches field day chickweed pressure and documented attendees about the findings of ALS herbicide resistance in common chickweed populations escapes from ALS inhibitors showed found in the southern San Joaquin Valley with real-life demonstrations of these weeds survivClark, Dias and Hanson that herbicide ing various ALS inhibitor herbicide applications. resistance could not be ruled out as a potential cause of the escapes. In that field, Clark and Dias applied tribenuron Fresno State students Paola Vidales, Kiera about the confirmation of common methyl (Dupont Express Herbicide with Searcy and Jennifer Vidales confirmed chickweed populations in California that Totalsol Soluble Granules) and pyroxsuwhat PCAs worried about. The common are genetically resistant to ALS inhibitors, lam (Simplicity CA), two frequently used chickweed identified as ALS inhibitor and 2) the research team gleaned importALS inhibitors in California, at two and escapes was in fact genetically resistant ant insights from the ag professionals’ four times the highest allowable label rate. to tribenuron methyl and pyroxsulam feedback. That feedback has been critical Clark and Dias observed that tribenuron (Heap 2023). in guiding ongoing research. slightly reduced the common chickweed growth and pyroxsulam had virtually no The UCCE and Fresno State team Future Directions effect when compared to an untreated observed that the ALS inhibitor resisThe two different responses between the control (Figure 2, see page 12). This evitant common chickweed responded to herbicides gave clues to the researchers dence warranted more intensive studies increasing doses of pyroxsulam but not about the ways the plants were expressing on common chickweed populations with to tribenuron methyl. When the dose of resistance to the herbicides. Fresno State ALS inhibitor escapes. Clark partnered pyroxsulam was increased up to eight professor Katherine Waselkov, specialwith California State University, Frestimes the max label rate, the treated com- izing in genetics of herbicide resistance, no Professor Anil Shrestha to conduct mon chickweed became more stunted joined the team to begin exploring the gecontrolled environment trials. These were and more of the plants died. Because the netic basis of this problem in California. designed to learn whether these weeds plants were not controlled with the maxThe major question Waselkov is researchwere resistant to ALS inhibitors. imum allowable rate, they are considered ing is whether the Central Valley popuresistant. When using tribenuron methyl, lations of chickweed showing resistance Seeds were collected by Clark and techthe common chickweed plants sprayed to ALS inhibitors have mutations in the nicians Ben Halleck (UCCE) and Walter with eight times the max allowable label ALS gene, which codes for the enzyme Martinez (Tulare County) from common rate appeared the same and survived targeted by the herbicides. By extracting chickweed in ALS inhibitor escape fields as much as plants sprayed with half the DNA, conducting PCR and sequencing and an organic field where there was no label rate. Many of the plants survived the entire ALS gene, the lab can detect recent ALS inhibitor application. The the herbicide applications and eventually possible resistance mutations that occur organic seeds were ALS inhibitor suscep- flowered, suggesting they may be reproin this enzyme. Changes in several amitible controls because their population ductive. no acids that directly interact with the was not pressured to evolve resistance. herbicides are likely to cause resistance.

The weed seeds were planted in pots in The UCCE and Fresno State team held These changes have been detected in a greenhouse and grown under a shade public field days at Fresno State. Product other countries’ chickweed infestations structure at Fresno State until they reps, PCAs and students gathered to (Marshall et al. 2010; Laforest and Soufireached the ideal growth stage for ALS observe the results of the study (Figure ane 2018). Waselkov’s different approach inhibitor control. After several exper3). The value of the field day was two-fold: will also screen for other less common iment repetitions, Clark, Shrestha and 1) ag professionals and students learned mutations that could cause resistance.

14

Progressive Crop Consultant September / October 2023

Pyroxsulam and tribenuron methyl are not the only ALS inhibitor herbicides used in small grains. Industry professionals pointed out mesosulfuron-methyl (Osprey Herbicide), although used less commonly, is also regularly applied to small grains. Additionally, it was pointed out that small grain fields where common chickweed was resistant to ALS inhibitors were recently rotated out of or into alfalfa, a common rotation partner, where multiple ALS inhibitor herbicides are applied to control several important weeds. For these reasons, the UCCE and Fresno State team continues to expand the controlled environment study to determine the presence of ALS inhibitor resistance in common chickweed with more herbicide products.

Fresno State Masters student Jennifer Valdez-Herrera is earning a degree in plant science through further study into ALS inhibitor resistance in common chickweed in California. Studying under Shrestha, Waselkov and Clark, Valdez-Herrera is addressing all the issues

above in addition to studying the impact that uncontrolled common chickweed has on yield and quality of small grains.

Growers and PCAs are apt to point out ALS inhibitors are a very important tool for controlling multiple serious weeds in small grains and alfalfa. Further, there are still several other herbicide modes of action registered for California small grains and alfalfa which have activity against common chickweed. The PCAs are the first line of defense in the field and the first consultants for knowledge about how to remedy weed problems. Our team continues to consult PCAs to guide future research endeavors in this field to make sure the solutions we seek are relevant and applicable to the industry.

References

Dias, J. L. C. dS., Clark, N., Mathesius, K., Light, S., Hanson, B., Lundy, M. E., Shrestha, A., 2021. Poor control of common chickweed with ALS-inhibitor herbicides reported in multiple small grain fields in the southern San Joaquin Valley. Is

it a new case of herbicide resistance in California? UC Weed Science Blog. Retrieved 7/28/23, https://ucanr.edu/blogs/blogcore/ postdetail.cfm?postnum=50181.

Heap, I., 2023. The International Herbicide-Resistant Weed Database. Retrieved 7/28/23, http://weedscience.org/Pages/ Case.aspx?ResistID=24253.

Laforest, M., and B. Soufiane. 2018.

Coevolution of two sulfonylurea-resistant common chickweed (Stellaria media) biotypes with different mutations in the acetolactate synthase gene. Weed Science 66: 439-445.

Marshall, R., R. Hull, and S. R. Moss.

2010. Target site resistance to ALS inhibiting herbicides in Papaver rhoeas and Stellaria media biotypes from the UK. Weed Research 50: 621-630.

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15

BIOSTIMULANTS B AND THE ROLE OF CYTOKININ IN CROP PERFORMANCE

iostimulant products come from things existing in nature which are useful as solutions to agricultural problems. They are seen as ways to meet challenges in nutrient use efficiency, managing crop stresses and arriving at the end goal of improving crop yield and quality.

By KIRK VAN LEUVEN | PCA, CCA

Citrus leaf senescence caused by magnesium deficiency manifests when cytokinin and chlorophyll are oxidized out of leaves (all photos courtesy K. Van Leuven.)

16

Progressive Crop Consultant September / October 2023

These products have created some tension in the agricultural community, particularly around regulatory requirements because they don’t fit squarely into either of the two traditional crop input categories. They’re not fertilizers and they’re not pest control chemicals.

The crop input industry is organized around these historical categories. So where do biostimulants fit in and how do we begin to understand how to work with them?

Admittedly, overreliance on fertilizers and chemicals creates several problems for agriculture. With yield and quality being the goal of everyone involved, biostimulants can supplement vigor and

crop resilience and improve yield and quality while reducing the environmental load of potentially harmful materials.

The newer science of molecular biology helps us to understand what goes on in the machinery of a plant as it reacts to its environment. Depending on conditions and the availability of nutrients and other essentials, the plant’s genetic code conducts its commitment to growth, using polarity and gravity as directional forces. Von Liebig understood 200 years ago how nutritional shortages could limit yield. What we understand now is that nutrition is only part of the equation. We can have soil nutrient levels at optimum and still have growth stalled out if other requirements are not met. At the center of it all is the genetic code. The rate of growth depends on signaling by hormones and the activation of genes inside the plant as it senses conditions around it. Gene activity is increased, or suppressed, in response to nutrient status and other factors like hormone concentration and environmental conditions. It has been estimated that over 30% of all the genes in higher plants have something to do with hormones.

Cytokinin in the Plant

One category of biostimulants is products which contain natural hormones like plant extracts and seaweed. The growth hormone cytokinin (CK) is an active component in some of these products. In the plant, the level of available CK can be increased in two different ways: stimulating synthesis of larger amounts of natural CK or adding exogenous applications of CK-containing materials. Applications of CK-containing seaweed products have become mainstream over the last 40 years. This can help with several plant processes at various stages of growth.

Natural systemic CK is produced primarily in the meristematic zones of the roots and apical growth points and is needed for cell division and other processes throughout the growth cycle.

It is needed for ongoing formation of all tissue and controls the size and shape

‘It’s well-established that the quality and size of fruits and nuts are improved by higher levels of [cytokinin] for cell division at fruit set and the early growth stages afterward.’

Almonds treated with foliar cytokinin on the right are consistently larger and heavier.

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like leafy vegetables, the size, quality and shelf life of the crop rely on a constant supply of CK during growth. CK is the hormone associated with holding back leaf senescence and is known as the juvenility hormone.

CK also regulates chlorophyll synthesis in the leaves, and increased CK is known to improve photosynthesis.

When we think about the influence that cell division also has on the size of the leaves, we realize CK is essential to the overall photosynthetic capacity of the plant. Photosynthesis is also supported longer in the growing season with senescence delayed by higher CK levels.

We will also discuss the role that CK has in the transport of sugars to other parts of the plant. CK is important for plant processes and growth throughout the plant’s life cycle.

Leaves and nuts on cytokinin treated almonds are uniformly larger and more photosynthetic with less senescence observed.

Continued from Page 17 of leaves, as well as the how the leaves are arranged on a stem. Whether plants grow from a crown or from a stock or

trunk they benefit from higher CK levels. CK determines the number of cells and potential size of a leaf. For crops

Besides the meristematic zones of the roots and apical tips, there is another place in the plant where CK is produced

Continued on Page 22

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part of the state, Scott said, and will no doubt make the event memorable.

“We expect this to be one of the best events that we’ve ever put on or will put on,” Scott said. “If you want to attend something that’s different, unique, and special to agriculture, this is the one time you need to make time to show up.”

the successes and failures of those issues so often being determined by politics.

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Scott's firm publishes both print and Scott added that he wants people to digital trade magazines. The publicawalk away with renewed relationships, tions include West Coast Nut, Grape & a better understanding of who ag is Wine and Progressive Crop Consultant. as an industry, and the challenges ag Scott's firms also hosts a growing web- faces collectively, as a group. site called MyAgLife, which highlights the diverse agriculture commodities of “I hope attendees will walk away with the West Coast. The site is also home a sense that not all is lost with conserto a daily and weekly podcast highvative values and we don’t stand alone Scott said he sees the night as a way lighting Central Valley ag issues and in that community,” he said to bring those who have a stake in leaders. agriculture together in one place to Tickets for My Ag Nite start at $150 celebrate the industry and to wind Coming out of a post pandemic reality, per person and a number of upgraded down and enjoy like-minded solidarScott came up with the idea for My Ag ticket opportunities are also availity following the stresses of the busy Nite as a way to stimulate live events, able, including a meet and greet with harvest season. he explained. Like the MyAgLife web- Watters, group table reservations, and site and brand, he emphasizes the event trade show booth space. Tickets and “We’re bringing a diversified group of being about agriculture as a whole, and further information can be obtained thought leaders together to celebrate not focusing on any one commodity. through www.myaglife.com/myagnite. leadership in agriculture,” he said.

Ag media inquiries only can be direct“We wanted to do something unique in ed to the JCS Marketing Office (559) Scott is especially excited about the the industry, for the industry, and we 352-4456. No outside media outlets event being able to present a rare, wanted to provide something for the beyond agriculture. in-person opportunity to hear from a MyAgLife brand,” he said. “The idea political commentator of Watters’ cali- behind it is that we celebrate agriculber that will appeal to the conservative ture and our conservative values in the farming community. Watters’ notoriety industry.”

About JCS Marketing: has skyrocketed since he took over for JCS Marketing has a rich history in former Fox News commentator, Tucker Scott says that while he tends to leave providing marketing services tailored to Carlson, who left the network earlier politics out of his publications and the agricultural industry. With a deep this year. marketing, he sees My Ag Nite as understanding of the unique needs and a way for those who have a stake in values of the ag community, they are The chance to see Watters speak isn’t agriculture to be able to talk about the committed to fostering connections and likely to come around again to this issues that affect them first hand—with driving success within the industry.

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Guests will have access to an exclusive trade show showcasing innovative farming solutions, and the opportunity to network and forge connections within the industry.

Continued from Page 18

movement of photosynthates and other solutes through the phloem. Phloem tissue has associated companion cells which are responsible for metabolism and the regulation of phloem function including sugar transport. These companion cells are connected to the sieve tube elements and form bridges to exchange signaling for the transport of sugars from source to sinks. Simply stated, the presence of CK in younger

and plays very important roles. That is in the points where any new vascular tissue is being developed. Vascular tissue conducts the movement of water, nutrients and other solutes throughout the plant. CK is not only required for the formation and growth of new vascular tissue, it is also a regulator in the

Corn lower leaf senescence indicates shortages of cytokinin as growth hormone is translocated downward to support growth of roots. Brace roots also indicate a shortage of growth hormone.

tissue is what calls for the movement of energy and nutrition from the source to the sink.

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Progressive Crop Consultant September / October 2023

7/13/23 4:16 PM

Similarly, in flowering crops, CK is needed for the development of reproductive tissue and can increase bloom and flower retention. During these times in the growth cycle when new tissue is developing, a spike in the pool of available hormones is necessary. When flowering takes place in unfavorable conditions, the strength of the flowers and pollen is limited by the lack of CK. If adequate hormones are not available, the genetic potential of the plant is compromised. Pollen quality improves with higher levels of CK. Fertilization and the cell division which takes place immediately afterward require available CK. It’s well-established that the quality and size of fruits and nuts are improved by higher levels of CK for cell division at fruit set and the early growth stages afterward. A tighter cell density at this stage contributes to improved size and quality after cell enlargement and crop bulking take place.

In Research

Several crops have to flower during

and bioidentical products containing CK, it serves as a great example of how biostimulant products can enhance and improve plant performance at different stages of growth. Increased understanding of plant physiology, molecular biology and genetics has led to many validations of biostimulant technologies to improve crop production and quality.

CK products are only one example of the biological and biostimulant prod-

hotter weather. Summer heat can take a toll on crop yield. Molecular research into the effects of high temperatures on crops during pollination was conducted by Stoller Group, now a division of Corteva Agriscience. It was found that genes responsible for production of enzymes which break CK down by oxidation become upregulated in the plant during higher temperatures. Under better conditions, as previously mentioned, the amount of CK in the plant peaks at the time of flowering to assist in the process of fertilization. Lower CK during hot weather diminishes pollen strength and reduces the shedding of pollen, and the resulting weakened embryos have a higher potential to abort. Infertility of flowers can result from heat-induced male sterility. Stoller found supplying exogenous CK provided significant improvement to pollination during heat events. This strategy has been used extensively to improve pollination and grain or fruit set across a wide variety of crops by Stoller agronomists since this discovery 10 years ago.

CK is a biostimulant with benefits that have been discovered and researched extensively. Because of the many natural

ucts which are entering the market and emerging as solutions to the problems of water and nutrient use efficiency, stress management, weather resistance and other improvements to crop yield and quality.

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23

Do Wider Beds in Fresh Market Onion Production Increase Total Water Productivity?

By JAIRO DIAZ | Director, UC ANR Desert Research and Education Center, DANIEL GEISSELER | UCCE Nutrient Management Specialist, and ROBERTO SOTO| Faculty Member, Universidad Autonoma de Baja California

Figure 1. Onion sizes (L-R prepack, medium, jumbo, colossal and super colossal) per season. Terena in 2019-20 (top), and Hornet in 2020-21 (bottom).

I

mperial County, located in Southern California, has a large agricultural sector with close to 500,000 acres in production. The region’s major agricultural sectors are cattle feedlots, forages and vegetables. Imperial County and surrounding areas produce an estimated two-thirds of the nation’s vegetables in the winter. In the last decade, the use of pressurized irrigation systems (solid set sprinklers and drip irrigation) and wider beds in vegetable production has gained popularity in Imperial County. Imperial County is a top fresh market onion region with over 3,000 acres in annual production. Agriculture in Imperial County relies on just one water source:

Table 1.

Growth stage

Days after planting

Emergence

0-30

0.40

Two/three leaves to bulb development

45-165

0.84

Bulb fully developed to dry leaf stage

170-harvest

0.62

Table 1. Growth stage onion crop coefficient values used in this study (Montazar 2019).

the Colorado River. As the Colorado River basin (CRB) is reaching more Table than 202.years of continuous drought, the US Bureau of Reclamation is working Cultivar Rainfall with basin users toPlant-Harvest develop strategies (in) that may reduce water usage between 2 and 4 million per– year. Most Terena acre-feet 10/24/2019 4.7 5/1/2020

24

Crop coefficient

Hornet

10/27/2020 –

Progressive Crop Consultant September / October5/3/2021 2023

1.3

of the projected water cuts are expected from agriculture due to its high share of water use. Agricultural users and water regulators in the CRB are discussing Irrigation GDD* strategies to promote water conservation (oF-d) practices improve water use efficien100% ETc (in) and 130% ETc (in) cy15.9 while keeping a18.9large and productive 2,948 21.4

24.6

3,003

*GDD = growing degree days was based on a minimum base temperature of 42.8 degrees F and a

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agricultural sector that feeds Americans with high-quality food all year long. The objective of this study was to assess the effect of two bed sizes and two irrigation amounts on onion yield and water productivity.

Zn Mn

Methods

This study was performed during two growing seasons (2019-20 and 2020-21) at the UC Desert Research and Extension Center (DREC) in Holtville, Calif.

The major soil unit in testing areas is a Holtville clay with clay, silt and sand proportions of approximately 42%, 19% and 39%, respectively.

Two irrigation levels were evaluated: 100% and 130% of crop evapotranspiration (ETc). ETc was computed using potential evapotranspiration from the California Irrigation Management Information Systems (CIMIS) station at DREC (Meloland station #87) and adjusted by stage-specific crop coefficients (Table 1, see page 24) developed

by Ali Montazar (2019) for Imperial County onion production. This study used sprinkler irrigation for crop emergence and until the beginning of bulbing to ensure an adequate establishment. This is a normal practice in our region. Irrigation treatments using drip

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Continued on Page 26 September / October 2023 www.progressivecrop.com

25

Continued from Page 25

.

ultivar

Terena

Table 2. Onion cultivars, seasonal conditions and irrigation amounts per season.

Table 2.

Plant-Harvest

Rainfall (in)

Irrigation

100% ETc (in) Plant-Harvest Rainfall 4.7 15.9 (in)

Cultivar 10/24/2019 – 5/1/2020

10/24/2019 – 1.3 5/1/2020

Irrigation 18.9 2,948 100% ETc (in) 130% ETc (in)

21.4 4.7

15.9 24.6

GDD* (oF-d)

3,003 18.9

2,948

Hornet – 21.442.8 degrees F and 24.6 = growing degree days was based10/27/2020 on a minimum base1.3temperature of a 5/3/2021 um temperature of 68.0 degrees F. ETc = crop evapotranspiration.

3,003

Hornet

Terena 10/27/2020 – 5/3/2021

GDD* (oF-d)

130% ETc (in)

*GDD = growing degree days was based on a minimum base temperature of 42.8 degrees F and a maximum temperature of 68.0 degrees F. ETc = crop evapotranspiration.

Table 3. Plant density by cultivar and bed size.

.

Table 3. Cultivar

Terena Hornet

Plant Density (onions/ac) 40 in Cultivar 118,300 98,000 Terena Hornet

Table 4.

80 in

Plant Density (onions/ac) 175,400 40 in 80 in 149,600 118,300 175,400 98,000

149,600

Table 4.

Table 4. Effect ofIrrigation irrigation rates on freshMedium market onion size distribution and total yield.

Cultivar/Year Prepack Jumbo Colossal Super Total Level Colossal (bed size) Cultivar/Year Irrigation Prepack Medium Jumbo Colossal Super Total ton/acre Level Colossal (bed size) Terena/ 100% ETc 0.6 5.8 32.4ton/acre 9.7 2.0 50.6 2019-2020 (40 130% ETc 0.6 4.8 31.2 12.6 3.1 52.4* Terena/ 100% ETc 0.6 5.8 32.4 9.7 2.0 50.6 in) 2019-2020 (40 130% 0.6 4.8 31.2 12.6 3.1 52.4* Terena/ 100%ETc ETc 1.5 19.2* 33.9 1.3 0.0 55.9 in) 2019-2020 (80 130% ETc ETc 1.3 11.1 46.8* 6.3* 2.8** 68.2** Terena/ 100% 1.5 19.2* 33.9 1.3 0.0 55.9 in) 2019-2020 (80 130% 1.3 11.1 46.8* 6.3* 2.8** 68.2** Hornet/ 100%ETc ETc 0.9 9.2* 12.5 6.0 4.7 33.3 in) 2020-2021 (40 130% ETc ETc 0.7 7.4 18.1** 5.9 5.0 37.0* Hornet/ 100% 0.9 9.2* 12.5 6.0 4.7 33.3 in) 2020-2021 (40 130% ETc 0.7 7.4 18.1** 5.9 5.0 37.0* Hornet/ 100% ETc 0.6 21.4 21.2 0.2 0.0 43.5 in) 2020-2021 (80 130% ETc 2.0* 17.5 21.3 1.3 0.0 42.1 Hornet/ 100% ETc 0.6 21.4 21.2 0.2 0.0 43.5 in) 2020-2021 (80 ***Onion bulbs were 130% ETc 2.0* 17.5 than 2.5 21.3 1.3 (2.5 to 3.25 0.0 42.1 categorized as prepack (less in), medium in), jumbo (3.25 in) to 4 in), colossal (4 to 4.25 in), and super colossal (greater than 4.25 in) based on bulb diameter. ***Onion bulbs were categorized as prepack (less than 2.5 in), medium (2.5 to 3.25 in), jumbo (3.25 Significant levels *, ** indicate significance at 0.05 and 0.01, respectively, according to t-test. ETc = to 4 in), colossal (4 to 4.25 in), and super colossal (greater than 4.25 in) based on bulb diameter. crop evapotranspiration.

Significant levels *, ** indicate significance at 0.05 and 0.01, respectively, according to t-test. ETc = crop evapotranspiration.

Table 5. Total yields and water productivity by cultivar.

Table 5.

(Year) TableCultivar 5.

Irrigation Level

Total Yields

(ton/ac)

Total Water Productivity (ton/ ac-in) Total Water Productivity (ton/ 40-in ac-in) 80-in

Cultivar (Year)

Irrigation Level

Total Yields 40-in

(ton/ac) 80-in

Terena (2019-2020)

100% ETc

50.6 40-in

55.9 80-in

2.5** 40-in

2.7 80-in

Terena (2019-2020)

130% ETc ETc 100%

52.4* 50.6

68.2** 55.9

2.2 2.5**

2.9 2.7

Hornet (2020-2021)

100%ETc ETc 130%

33.3 52.4*

43.5 68.2**

1.5 2.2

1.9** 2.9

Hornet (2020-2021)

130% ETc ETc 100%

36.9* 33.3

42.1 43.5

1.4 1.5

1.6 1.9**

Significant levels *, ** indicate significance36.9* at 0.05 and 0.01, to t-test.

130% ETc 42.1respectively, according 1.4 1.6 ETc = crop evapotranspiration.

Significant levels *, ** indicate significance at 0.05 and 0.01, respectively, according to t-test. ETc = crop evapotranspiration.

26

Progressive Crop Consultant September / October 2023

systems were established in January of every season. Water amounts delivered through the drip irrigation system were computed using a daily water balance approach (irrigation needs = ETc - rainfall). Drip irrigation treatments started at bulb initiation (about eight leaves and a bulb diameter that was twice that of the neck.) Onion yields and sized distribution were measured at harvest.

A two-sample t-test was performed to compare irrigation levels per bed size with SAS software. Total water productivity (TWP) was computed for each irrigation treatment. The TWP included rain and irrigation amounts. The TWP was computed as the total fresh onion yield divided by the total water use.

The drip tape was installed between 2- and 4-inches depth. One drip tape line was installed near the center of the 40-inch bed. Three drip tape lines were buried in the 80-inch bed plots. 4 and 12 lines of onions were planted in the 40inch and 80-inch bed rows, respectively.

Research plots were 50 feet long and comprised four rows on 40-inch beds and three rows on 80-inch beds.

Results and Discussion

Table 2 shows onion cultivars, seasonal conditions and irrigation amounts per season. Terena and Hornet varieties are short-day, yellow hybrid onions (Figure 1, see page 24). Terena variety has a globe shape and Hornet is a grano-shaped onion.

Plant density used in this study is in the range used by growers in Imperial County (Table 3). Plant density on 80inch beds was about 50% higher than onions planted on 40-inch beds.

Total yields responded to irrigation amounts except in the trial with Hornet (2020-21) on 80-inch beds (Table 4). In the Hornet trial (2020-21) on 80-inch beds, we noticed the irrigation treatment using 130% ETc yielded a higher proportion of pre-pack sizes compared to other treatments. We also noticed Hornet grown on 80-inch beds did not yield super colossal sizes. These results indicate

Hornet seeds were planted too close in the 80-inch beds, reducing bulb size in the higher-irrigation treatment.

Terena treatments in 2019-20 produced a larger proportion (63% to 90%) of high-value bulbs (jumbo, colossal and super colossal) than Hornet in 202021(49% to 78%). High-value bulbs produced by irrigation treatments at 130% ETc were consistently higher than in the 100% ETc treatments. When onions were sorted by sizes and per-unit yields were computed, Terena’s yields were approximately 20% higher than Hornet’s yields.

Highlights • Terena variety produced higher yields than Hornet variety.

• High-value bulbs (jumbo, colossal and super colossal) produced by irrigation treatments at 130% ETc were consistently higher than with 100% ETc. • Total water productivity did not increase as irrigation levels increased regardless of bed size.

• Fresh market onions on 80-inch beds were more water efficient than onions produced using 40-inch beds.

Montazar, A. 2019. Preliminary estimation of dehydrator onion crop water needs in the Imperial Valley. Agricultural Briefs 22(7):131-135. University of California Cooperative Extension – Imperial County.

This research included funds from the California Department of Food and Agriculture’s Fertilizer

For more information, contact Jairo Diaz at jdiazr@ucanr.edu or 760-791-0521.

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

Scan to learn more

Irrigation levels did not affect total water productivity (TWP) for Terena (201920) grown on 80-inch beds and Hornet (2020-2021) grown on 40-inch beds (Table 5, see page 26). Total water productivity decreased as irrigation increased in the following trials: Terena (2019-20) on 40-inch beds and Hornet (2020-21) on 80-inch beds. Total yields on 80-inch beds increased between 10% and 31% compared to total yields on 40-inch beds (Table 5, see page 26). Total water productivity was higher when onions were harvested on 80-inch beds than onions produced on 40-inch bed systems.

Total water productivity of onions using 80-inch beds increased between 8% and 32% compared to onions grown on 40inch beds.

Research and Education Program.

References

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27

Navel Orangeworm Hullsplit Spray Considerations in 2023

By SUDAN GYAWALY | UCCE IPM Advisor, Northern Sacramento Valley

If the beginning of Nonpareil hullsplit coincides with egg laying time of the second flight of NOW, the risk of NOW damage increases. (all photos by Vicky Boyd.)

28

Progressive Crop Consultant September / October 2023

F

rom the standpoint of navel orangeworm (NOW) management in almonds, hullsplit is the most critical fruit developmental stage. Almond fruits open at their suture during this period and become susceptible to NOW infestation. If the beginning of Nonpareil hullsplit coincides with egg laying time of the second flight of NOW, the risk of NOW damage increases. Therefore, understanding NOW activity and hullsplit status is vital for timely insecticide applications.

The nuts on the southwest side of the canopy mature earlier, so the initiation of hullsplit in a block should be confirmed by regularly checking on the southwest side of the canopy. An orchard ladder or pruning tower can aid in reaching the fruits from the top of the representative trees to detect early split. Also, knowing the difference between true hullsplit and blank nut split is essential because blank nut hullsplit usually begins one to two weeks before the sound nut hullsplit begins. Nuts in edge trees, especially on the southern edge of an orchard, often start to split several days to a week ahead of trees within the orchard. Edge and blank splits signal the approach of hull split of sound nuts inside the orchard. Hullsplit timing varies among tree water status, varieties, geographic regions and weather conditions; however, prediction models are available to predict hullsplit timing for various locations. Research and field experience tell us that spraying earlier, rather than later, is the most effective strategy for reducing NOW damage.

NOW Traps and Spray Decision

NOW monitoring (egg, male and female) traps do not provide a specific treatment threshold; however, they can be highly beneficial for spray decision-making since they inform the grower about seasonal pest activities. Egg traps are helpful to set the egg-laying biofix for overwintering adults in the spring and track the heat units to determine the completion of that generation and the beginning of the second generation (i.e., 1050 degree-days).

The second generation infests the early hullsplit nuts, and the timing for that generation is critically important to minimize the nut damage. The utility of egg traps for guiding spray timing would be less clear for the later generations

because of the continuation of egg-laying due to overlapping adults among generations. However, the density of egg laying in egg traps and female moth activity (in Peterson traps or similar tools) are good indicators of potential NOW pressure and, possibly, nut damage.

Experience shows that unless an orchard is in an isolated location with a history of very low NOW damage and low NOW population, most almond orchards in

the Northern Sacramento Valley warrant at least one spray at hullsplit. However, missing proper spray timing and not practicing other cultural practices such as winter sanitation may result in higher-than-acceptable levels of nut damage.

Therefore, minimizing NOW damage requires practicing cultural techniques, such as winter sanitation and timely harvest, monitoring pest populations

Continued on Page 30

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Continued from Page 29

Table 1.

and making well-timed insecticide sprays. Once hulsplit begins and eggs are being laid in egg traps, spray to protect early hullsplit, watch traps tracking females (egg and/or Peterson traps) and check early split nuts for worms to make preharvest spray decisions and decide on harvest timing. If NOW pressure is high, it might be worth a talk with the processor to look at timely harvest and kernel (meats) production vs later harvest for inshell. If NOW pressure is high, damage can increase very rapidly, and every day the nuts are in the trees increases the danger of further damage.

Determining Spray Timing and Numbers

The number and timing of hullsplit sprays depend on orchard history, in-season pest monitoring information, use of other cultural practices such as winter sanitation and timely harvest, and overall risk of NOW immigration to the orchard. Typically, the first hullsplit spray for NOW is made when the eggs are being laid and the hullsplit begins. Commonly used, relatively reduced-risk insecticides only kill eggs and larvae. Some are effective against adults; however, insecticides must contact adults to be effective. Spraying during the night or early morning is more effective than spraying during the day. These insecticides can be effective for two to four weeks; a second application may be necessary if you continuously find high numbers of eggs, females and males in their respective traps and you cannot harvest the nuts before the third flight activity. Early hullsplit

Disclaimer: Products listed in this table do not constitute a recommendation, and many of the active ingredients presented in this article can be purchased under multiple trade names.

pollinizers split about two weeks after Nonpareil; the hullsplit typically starts when the NOW third flight begins. For many growers requiring a second hullsplit spray, a second application can help both Nonpareil and pollinizers. Late-season pollinizer varieties can be at risk from the latter portion of the third and fourth flights if not harvested on time.

Additional Considerations

Provide good spray coverage. Good spray coverage is essential for effective NOW control. Many years of study have indicated spray coverage is the function of tree height, sprayer speed and spray volume. In mature almond orchards, it has been shown that high-volume spray (150 to 200 GPA ) with a slower spraying speed (2 mph) provides better coverage and NOW control, though it is an unconventional practice for many growers.

Harvest on time. The goal of timely harvest is to get the almond harvested once 100% hull split occurs for all varieties, and if possible, before the beginning of the third generation for Nonpareil and before the fourth generation for other late varieties.

Ensuring that nuts are at the proper maturity stage during the harvest is critical. Too early harvest can lead to mold development and chipping issues during the processing, reducing the nut quality.

Know your insecticides. Insecticides differ in their mode of action, efficacies to NOW and toxicity to beneficials (Table 1).

Knowing those facts can help select the best insecticide for a particular situation. Most of the insecticides labeled for NOW target newly hatched larvae and have some impacts on eggs.

30

Progressive Crop Consultant September / October 2023

Some have effects on all stages. Insecticides applied for NOW management at hullsplit must kill the egg or larva before feeding damage occurs. Another difference among NOW insecticide is their potential effects on spider mite predators such as predatory mites and sixspotted thrips. Non-selective insecticides, in general, are more toxic to those beneficial than selective insecticides. Therefore, the tradeoff of using broad-spectrum insecticide should always be considered.

Understand seasonal changes in NOW biology and behavior. NOW development rate changes during the season. The first and second generation of NOW needs about 1050 degree-days to complete one generation. However, after that, NOW can complete a generation in only 750 degree-days due to better nutritional quality offered by the fresh nuts. Temperature plays a significant role, too, as higher temperatures during the summer accelerate egg hatching and larvae development.

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31

Tips for Managing Vine Nutrition in Vineyards

By TIAN TIAN | UCCE Viticulture Farm Advisor, Kern County

P

roper nutrition management allows vines to grow healthy canopies and produce fruit with desirable quality.

Fertilization is used to correct nutrient deficiency and improve vine productivity. Even in vines without foliar symptoms, growers may fertilize as a routine practice to compensate nutrient loss at harvest and prevent nutrient deficiency.

As a result, sometimes managing vine nutrition simply means applying fertilizers. I would argue that understanding vine nutrient status and determining their nutrient needs are as important as fertilization itself.

Understanding vine nutrient status and determining their nutrient needs are as important as fertilization itself (all photos by T. Tian.)

Grapevines have lower fertilization requirements than many agricultural crops. Overfertilization does not offer many benefits from economic or vine productivity points of view.

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In terms of macronutrients, annual growth is a strong sink for nitrogen, phosphorus, potassium, calcium and magnesium between bud break and veraison.

trogen (N) as an example here. Excessive N additions lead to jungle-like canopy with limited light penetration and air circulation, increase disease pressure and negatively affect fruit quality. Excessive amounts of nitrate in the soil also increase the risk of groundwater and surface water contamination.

Supplying vines with ample but not excessive nutrients is easier said than done. In this article, I will start the story with summarizing previous work on whole vine nutrient budget and then extend the discussion to determining vine nutrient requirements and fertilization.

Whole Vine Nutrient Budget

Studies were conducted under field conditions in California and Oregon and in potted systems in South Africa to track nutrient uptake, movement and distribution among vine organs at different phenological stages.

In terms of macronutrients, annual growth is a strong sink for N, phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) between bud break and veraison. Required nu-

Progressive Crop Consultant September / October 2023

trients of shoots, leaves and clusters can be obtained from two pools: nutrients remobilized from permanent organs and those taken from soil. In mature vines, up to 50% of N and P in new growth can be supplied by the stored reserve in trunks and roots. On the other hand, less than 15% of K, Ca and Mg are remobilized from the reserve, since only a small percentage of those nutrients can be recycled during leaf fall. Clearly, nutrients obtained from the soil still account for a large portion of required nutrients, even in the mature vines.

Young vines have less nutrient reserve than older vines, and thus rely more on nutrients supplied by root systems.

Nitrogen uptake peaks between bud break and bloom, while uptake of other macronutrients usually reach the max between bloom and veraison. Nutrient uptake also takes place after harvest when nutrients are available in the soil and weather conditions are favorable.

The uptake and distribution of micronutrients is less understood as compared to macronutrients. Dr. Paul Schreiner, scientist at USDA-ARS, studies the budget of micronutrient in young and older ‘Pinot noir’ vines in Oregon’s Willamette Valley. In young vines, boron, zinc, manganese and copper were taken between bud break and harvest, with the peak of uptake occurring between bloom and veraison. The uptake and allocation of micronutrients appears less consistent in mature vines.

Please note that research findings reflect vine nutrient budget under specific conditions and should be interpreted with caution. Factors like soil nutrient availability, irrigation practices, rootstock and scion combination and weather conditions have large impacts on nutrient uptake and allocation. Clearly, vine nutrient demand varies between vineyards. So, how should one determine whether fertilization is needed at a specific site?

Determine Nutrient Requirement of Vines

Nutrient analyses of leaf blades and leaf petioles at bloom and veraison are indicators of vine nutrient status. Many

testing labs provide the comparison of leaf nutrient concentration to the normal range for each nutrient.

We recommend growers not relying solely on numbers on lab results to make fertilization decisions. First, variability in vine nutrient requirement is expected between vineyards and across seasons. Even if the tissue nutrient concentration of a vineyard is slightly below

the given normal range, it does not mean vines surely experience nutrient deficiency. Second, normal ranges of leaf nutrients are estimated in experiments where vines received a specific nutrient at different rates and had its concentration over a wide range of leaf tissues.

Given the difference in experimental setup, the normal range determined

Continued on Page 34

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33

Continued from Page 33 can vary between studies. Thus, the normal range for nutrients should be used only as references when it comes to interpreting vine nutrient requirements.

Historical nutrient data, vine growth and production goals are important to consider. For example, fast-growing canopies may have lower leaf N concentration, especially in newly expanded leaves, but does not mean that vines require N fertilization. Instead, rapid shoot growth often indicates ample N and water availability in the soil.

Fertilization

In vineyards where fertilization is needed, growers and CCAs often ask me about the amount, formula and application timing of fertilizer. Rather than providing generalized answers for those questions, I would like to share some tips. Please feel free to reach out for questions related to your vineyards.

34

About 3 lb N, 0.5 lb P and 5 lb K are removed from a vineyard with each ton of harvested fruit. Many would use those numbers to calculate how much fertilizer is needed to compensate the loss during harvest. In reality, supplementing vines only with nutrients removed from the vineyard may not be sufficient.

For instance, data from western Oregon showed that young ‘Pinot noir’ vines acquired 12.5 lb N, 3 lb P and 25 lb K per acre via uptake with the crop level at 2.0 ton/acre.

Compost is an affordable, slow-releasing fertilizer. Applying compost in the spring supplements vines with nutrients, boost soil microbial activity, improves soil water penetration by aggregation and enhances water holding capacity.

Increasing soil organic matter is good practice for soil health in general.

Soil pH plays key roles on nutrient availability. Most nutrients become more available in soils with neutral pH.

Progressive Crop Consultant September / October 2023

Regular soil sampling and testing can help with managing and adjusting soil pH if needed.

If nutrient deficiency is observed late in the season, immediate fertilization may not alleviate the symptoms. It is because the period when nutrient deficiency becomes evident would not be coincident with the period when nutrient uptake peaks. Making applications at the right timing in the following season may be more effective on correcting deficiency.

Even though vines obtain nutrients mainly from the soil by roots, foliar application can be an additional tool to supplement vines with nutrients. In the past, we successfully increased fruit N at harvest in wine grapes by applying urea to foliage between fruit set and veraison. Foliar application of P and Mg was found to reduce leaf symptoms in wine grapes. Some PCAs suggest foliar Ca and Mg sprays between bloom and veraison can increase berry firmness

Even if the tissue nutrient concentration of a vineyard is slightly below the given normal range, it does not mean vines surely experience nutrient deficiency.

and reduce powdery mildew occurrence in table grapes.

Applying fertilizers in small doses may improve fertilization efficiency in vineyards with shallow root systems.

Theoretically, frequent fertilization with lower doses allows roots to better catch nutrients and reduce leaching.

References

Araujo FJ and Williams LE. 1988. Dry matter and nitrogen partitioning and root growth of young field-grown Thompson Seedless grapevines. Vitis 27:21-32.

Conradie WJ. 1980. Seasonal uptake of nutrients by Chenin blanc in sand culture: I. Nitrogen. S Afr J Enol Vitic 1:59-65.

Conradie WJ. 1981. Seasonal uptake of nutrients by Chenin blanc in sand culture: II. Phosphorus, potassium, calcium and magnesium. S Afr J Enol Vitic 2:7-14.

Schreiner RP, Scagel CF and Baham J. 2006. Nutrient uptake and distribution in a mature ‘Pinot noir’ vineyard. HortScience 41:336-345 Schreiner RP. 2016. Nutrient uptake and distribution in young Pinot noir grapevines over two seasons. Am J Enol Vitic 67:436-448 Comments about this article? We want to hear from you. Feel free to email us at article@jcsmarketinginc.com

September / October 2023 www.progressivecrop.com

35

Challenges and Prospects for Biopesticide Discovery

By PHILIPPE ROLSHAUSEN | Ph.D., Professor of Cooperative Extension, Department of Botany and Plant Sciences, UC Riverside

T

he world population is projected to reach about 10 billion individuals by 2050. As a result, the agricultural sector needs to produce more food despite several looming challenges, including the shrinking of arable land, erratic and extreme weather patterns and pest and disease outbreaks. Higher agricultural outputs per surface basis is one key element to solve the equation of a growing demand, which inevitably results in an increase of agrochemical inputs (pesticides, fertilizers). The global agrochemical market size is valued at $235.2 billion in 2023 and is expected to reach $280 billion by 2028, growing at a compound annual growth rate (CAGR) of 3.7% during the forecast period. The major driving force behind this uptrend comes from the organic sector. Hence, the global agricultural biologicals market (biopesticides, biostimulants and biofertilizers) is projected to grow at a CAGR of 13.8% to reach $27.9 billion by 2029 from $14.6 billion in 2023.

There is a growing consumer demand for organically grown and safe agricultural products. There is also a collective awareness of the potential risks associated with pesticide use, including impact on human health (e.g., increase of cancers linked to pesticide use), contamination of environmental resources (e.g., leaching of chemicals in groundwater) and non-target side effects on wildlife (e.g., bee population collapse).

This has led to a tightening of policies by governments and regulatory agencies for conventional chemical use and chemical residue limits and the phasing out of harsh synthetic agrochemicals. Growers are at the forefront of the sustainable ag movement and have adapted their farming practices to meet both consumer and agency demands. Replacing synthetic chemicals with organic products or biologicals in their agrochemical ar36

senal can be challenging because of the limited scientific information on their mode of action and range of efficacy. In this article, we will mostly focus the discussion on sustainable strategies to control diseases with biopesticides, the discovery pipeline within the framework of my research and the prospects for the future.

In Integrated Pest Management

Fostering sustainable farming practices that promote and enhance agroecosystem health and increase biodiversity are instrumental to our long-term success.

Integrated pest and disease management programs (IPM or IPDM) have been central to this philosophy. The framework of IPM programs is to reduce synthetic agrochemical inputs and rely first on alternative strategies, such as adapted management practices, use of resistant/tolerant plant varieties and deployment of organic agrochemicals and biologicals. IPM programs were at times challenging to implement to manage certain crop diseases because of the lack of relevant alternatives to synthetic agrochemicals. Organic agrochemicals suffer from a short window of activity and under high disease pressure they must be applied often. Also, those products are not free of environmental risks. For example, the copper-based Bordeaux mixtures have been used for over a century in viticulture and are known to impoverish vineyard soil biota and affect aromas in wine. Biologicals also often suffered from a lack of credibility because of their inconsistency to control diseases. From a grower standpoint, there is too much economical risk to rely on uncertainty. However, recent scientific discoveries and technological advances have helped strengthen IPM programs in many ways. First, they have and continue to improve the formulations

Progressive Crop Consultant September / October 2023

of agrochemicals (conventional, organic and biological) and, most importantly, their deliveries to target pests and pathogens. Scientific reports indicated that only 0.1% to 1% of sprayed material reaches its target depending on the system. Thus, increasing delivery efficiency will reduce leaching of chemicals in the environment. Second, the advent of ‘omics’ technologies and affordability of sequencing costs have allowed industry to identify biological candidates in a quick and reliable manner. This has revolutionized the field of microbiology (among others) that traditionally used ancestral culturing techniques to single out biological agents from environmental samples, which equated to finding a needle in a haystack. In today’s era, we can generate large-sequence datasets that capture not only entire microbial communities associated with plants or environments but also shed light on their biological functions. To be able to see in a high-throughput manner ‘who does what’ has streamlined the discovery of biological products.

Finding Beneficial Microbes for Diseased Systems

My lab has been using omics tools to identify beneficial organisms inhabiting citrus and grapevine that could be leveraged to manage Huanglongbing (HLB) and Pierce’s disease (PD), respectively. Both diseases are caused by bacterial pathogens transmitted by insect vectors following feeding on the plant host. In citrus HLB, the bacterium (Candidatus Liberibacter asiaticus) lives in the phloem tissues that transport sugars downwards, from leaves to fruits and roots. In grapevine, the bacterium (Xylella fastidiosa) lives in the xylem tissues that transport water and nutrients upwards from roots to leaves.

In both pathosystems, the buildup of bacteria in the hosts’ vasculature leads

Figure 1. Microbial shift following decline of citrus trees caused by Huanglongbing (Ginnan et al. 2020).

to disruption of channel transport to a point that becomes detrimental to the plant. Citrus and grapevine decline can happen in as quickly as two years, but in some cases, the hosts can sustain the infection for several years. Our hypothesis is the microbial communities living with the host provide protection against the pathogens with the goal of leveraging their benefits for crop protection.

A survey of citrus orchards in Flor-

ida and sequencing of the microbial communities associated with roots of trees with a range of disease symptoms revealed interesting information on the disease etiology (Figure 1). Our results showed there was an initial decline of keystone taxa (native organisms that play a role in the stability of an ecosystem) and symbionts such as mycorrhizae fungi for trees that contracted the disease (Phase I). This was followed by a microbe-mediated response to infection,

with enrichment of several beneficial organisms that have the capabilities to stimulate the tree immune response or provide direct antibiosis to pathogens (Phase II). In the late phase of the infection (Phase III), we measured an increase of soilborne parasites and pathogens (Fusarium, Phytophthora) and saprophytic fungi that decompose

Continued on Page 38

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Continued from Page 37 decayed roots. Those findings indicate either HLB made trees more vulnerable to root pathogens or vice versa, but in either case, this synergistic effect caused trees to decline at a faster pace. This research led to the pursuit of two strategies that are now being evaluated to combat HLB. The first strategy is to re-introduce into the system beneficial microbes or microbial natural products isolated from Phase II and verify these can support tree immunity. The second strategy is to identify cultural practices like soil amendments that support the keystone and symbiotic communities.

Similar to citrus, we surveyed vineyards and profiled Figure 2. Microbial mediated response to grapevine Pierce’s disease (PD) infection. the microbiome of grapevine with a range of Pierce’s A) Mild PD infection; B) intermediate PD infection; and C) severe PD infection. Botdisease symptoms (Figure 2). Here, we found intertom panel shows the bacterial response to infection in intermediate PD infection esting data when looking at the vine lignified shoot (Deyett and Rolshausen 2019). tissues (canes). In comparison to the root system, there are very few microbes living in the plant vasculature and even more so in annual tissues like canes that are when those two beneficial bacteria were present and abundant, pruned off every year. This is a perfect environment for the the pathogenic bacterium was low, and vines were healthy. pathogenic bacterium to thrive due to the limited microbial Our group further re-isolated those beneficial bacteria and competition. Our results showed that, just like in citrus roots, confirmed in greenhouse bioassays that when they were there was a microbial-mediated response to infection and that inoculated to grapevine, they provided protection against two bacteria that also inhabit the vascular system correlated Pierce’s disease. These biological control agents are currently negatively with the pathogen Xylella fastidiosa. In other words, being evaluated at UC Davis in field trials. UC patented those technologies, and we are partnering with the private sector to develop injectable or sprayable products that could be commercialized for Pierce’s disease management.

SYNAGRO

There is a push from agricultural commodities to replace synthetic agrochemicals with environmentally friendly solutions. There are a lot of incentives for agrochemical companies to develop bio-based products, including an easier path to EPA registration. The lower residual toxicity levels of biopesticides make them the perfect choice to meet stringent environmental standards and address food safety and quality.

However, biologicals still suffer from higher production costs because they are not produced and distributed in high volumes like their synthetic chemical counterparts. Increasing scalability and improving consistency in efficacy are two major hurdles for biopesticides to gain larger market share in the future.

References

Ginnan et al. 2020. Phytobiomes. https://doi. org/10.1094/PBIOMES-04-20-0027-R

Deyett and Rolshausen 2019. Frontiers in Plant Science. https://doi.org/10.3389/fpls.2019.01246 Comments about this article? We want to hear from you. Feel free to email us at article@ jcsmarketinginc.com

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Progressive Crop Consultant September / October 2023

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Promote root growth and improve soil Improve nutrient absorption efficiency and fertilizer utilization Increase production and improve quality Drought and heat resistance Cold and waterlogging resistance Acid and alkali resistance Multicolor Crop

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