Research conducted by Imperial County CE Irrigation and Water Management Advisor Aliasghar Montazar was gathered under field conditions to give growers solid reference points for when and at what rate to irrigate and apply fertilizers in the low desert environment (photo by A. Montazar.)
More site-specific data on source, rate, timing and placement of nitrogen fertilizer in carrot production has been generated at the UC Desert Research and Extension Center in Holtville.
For many years, studies conducted in Canada were used to generate nitrogen uptake for the California carrot production system, leaving desert carrot growers in a very dissimilar climate, to rely on their own experience or on the Canadian studies for best practices in carrot fertilization.
Research conducted by Imperial County CE Irrigation and Water Management Advisor Alaiasghar Montazar, UCCE Nutrient Management Specialist Daniel Geisseler and Michael Cahn, UCCE irrigation and water resources advisor, developed information for desert growers based on their field locations, climate and production systems. Funding for the study was provided by the CDFA’s Fertilizer Research and Education Program and the California Fresh Carrot Advisory Board. The new research, based on local conditions, is expected to benefit carrot growers in Imperial and Kern counties where most of the state’s carrots are grown.
Reliable data gathered under field conditions gives growers solid reference points for when and at what rate to irrigate and apply fertilizers in the low desert environment, Montazar said. One of the key findings of the research was that carrots’ nitrogen uptake is generally low during the first 40 to 50 days after planting, suggesting to growers to limit their fertilizer applications during that period. Montazar said that by tailoring basic guidelines to their site-specific location, growers could maximize the amount of nitrogen taken up by the carrots and minimize the amount of nitrogen leached below the root zone.
”Improving irrigation and nutrient efficiency in the desert production system is what local growers are trying to achieve,” Montazar said. “With improved efficiency and reducing nutrient leaching, we can improve the quality of water in the Salton Sea.”
Montazar is also leading a research team in studying carrot production management practices under specific Kern County conditions and plans to complete that research in 2022.
The Imperial County study, “Spatial Variability of Nitrogen Uptake and Net Removal and Actual Evapotranspiration in the California Desert Carrot Production System”, is published in the journal Agriculture and can be found at doi.org/10.3390/agriculture11080752.
Findings and recommendations also appear in Progressive Crop Consultant: progressivecrop.com/2021/09/new-knowledge-based-information-developed-to-enhance-water-and-nitrogen-use-efficiency-in-desert-fresh-market-carrots/.
You must know the nutritional needs of your grapes to know how much to apply. Conventional wisdom is winegrapes use 9 pounds of nitrogen, 3 pounds of phosphorus and 13 pounds of potassium for each ton harvested (photo by Marni Katz.)
Winegrape growers are a very diverse group. Some growers grow for volume or high yield, not necessarily high quality. Some growers grow for high quality while yield is secondary. There are, of course, many growers in between. Maybe you are a conventional grower, or a sustainable grower, or an organic grower, or a biodynamic grower, or, well, you get my point. In order to understand your fertilizer needs, you must understand your goals. Let’s address how to build the right fertilizer program for your needs.
Know Your Needs
You must know the nutritional needs of your grapes to know how much to apply. Conventional wisdom is winegrapes use 9 lbs. of nitrogen, 3 lbs. of phosphorus and 13 lbs of potassium for each ton harvested. Again, there are slight differences from white or red and even varieties.
If you have established grapes, you must determine where you are at with the condition of your soil and quality of your water. Soil sampling is a yearly function as well as a water sample, no matter the source of the water. The amount of nutrients, or lack of, in the soil will help you realize what you need to do. Water quality needs to be known as well as the amount of nutrients in the water. Well water can contain some levels of nitrogen and other needed nutrients, but also excess salts and boron. The pH level of your water can affect the availability of nutrients in the soil as well as the fertilizers you apply. Since many fertilizers are applied through irrigation systems, pH becomes a big deal and causes fertilizer to separate in the system.
A CCA can help you get through these technical issues. How much fertilizer do I apply, what kind, when, and will it go through my system? A good advisor will also do in-season leaf samples to see where you are with the health of your grapes. These samples are done at specific stages of growth and even post-harvest. They are even doing sap analysis now to potentially give you another tool to determine plant health.
Know Your Method
Now that you know where you are at with soil and water, what kind of fertilizer do you use? Your irrigation system becomes your main way of applying fertilizers, so liquids become your primary type. Remember, with the fertilizer going in with the water, it will be next to the roots and will be taken up at the same time as the water. This is very efficient and sustainable.
Sometimes, you have to use dry sources because there are some forms that don’t mix well. You can band them on with ground spreaders that will lay a band down next to the row. Potassium is one type that is done this way. Soil amendments such as gypsum, lime and sulfur would be another example of soil applied as well as compost.
So, let’s say you want a five-ton crop to achieve your yield and quality goals. Reviewing your soil samples, previous-year leaf samples and post-harvest application of fertilizer, you now have an understanding of what you need to do.
You now want to apply through your drip system 45 lbs N, 15 lbs P and 65 lbs K. You might also want to put on some zinc, iron and sulfur. Your advisor and fertilizer supplier can design a liquid mix that will contain all of these nutrients. If your water source is good, you know these materials will not separate and can be applied safely.
Time Your Applications
Timing your applications can be tricky because you don’t want to apply the full amount at one time. Many growers don’t start watering until after bloom, and if it was a wet winter, it can be even later. Your post-harvest application is done to give the grapes the start-up they need if you have to wait to do the first watering the next year.
To achieve yield and quality goals, reviewing soil samples, previous-year leaf samples and post-harvest application of fertilizer is necessary (photo courtesy Lodi Winegrowers Workbook 2nd Edition.)
We know the greatest uptake of both water and nutrients is during the prebloom and bloom period. Nitrogen is perhaps the most important nutrient during this time period, and using a fast source of nitrogen is important. Look at a calcium nitrate source for speed, but be weary of what you can mix with it. You will probably need to put at least 30% of your N needs in the first watering and spread the balance over the next two to three irrigations. Remember this is just an example of what can be done to achieve your goals.
Overcoming Obstacles
What about obstacles like high pH water, or you only irrigate three times a year, or you have poor-drainage soil that doesn’t take water well? These and other issues have to be addressed as part of your overall farming operation. Your CCA is skilled and trained in these areas and can put into place an overall plan to modify these issues.
Soil amendments, such as gypsum, sulfur or lime, can help modify the soil to help it take water better and provide some of the other nutrients grapes need. If you want to apply compost, you minimize multiple applications by having the gypsum, sulfur or lime mixed with the compost so you can do one application per year with ground application equipment. Remember, we are trying to reduce our application by ground to limit our carbon footprint and be more sustainable.
Finally, the methods I have discussed work for all types of grape farming; only the sources of the nutrients change. Organic sources like nitrogen are much lower in analysis, so higher volumes are required to achieve the levels I have discussed. Mix ability can also be a concern; again, a good CCA knows about these issues and can get you going in the right direction. Organic generally requires more ground application for some of the types of fertilizers required, so combining the products together to reduce applications is important. Organic farming does not necessarily have a reduced carbon footprint, so trying to combine nutrient sources is important.
This information is broad and each vineyard is different. When you spray for pests, you generally use the same products on all blocks. When it comes to nutrition, all blocks are different, and it can even be broken down by varieties even if they are in the same block. Soils are not all the same, and when you sample, you find that out and react accordingly. I did not mention foliar nutrients; that is a whole different topic and will be saved for another time. Finally, fertilization is an art and can increase yields and quality when done properly. Remember your goals and then act accordingly.
Botrytis fruit rot or gray mold caused by Botrytis cinerea is a common fungal disease of strawberry and other crops damaging flowers and fruits. This pathogen has more than 200 plant species as hosts producing several cell-wall-degrading enzymes, toxins and other compounds and causing the host to induced programmed cell death (Williamson et al. 2007). As a result, soft rot of aerial plant parts in live plants and postharvest decay of fruits, flowers and vegetables occurs. Pathogen survives in the plant debris and soil and can be present in the plant tissues before flowers form. Infection is common on developing or ripe fruits as brown lesions. Lesions typically appear under the calyxes but can be seen on other areas of the fruit. As the disease progresses, a layer of gray spores forms on the infected surface. Severe infection in flowers results in the failure of fruit development. Cool and moist conditions favor botrytis fruit rot development. Sprinkler irrigation, rains or certain agricultural practices can contribute to the dispersal of fungal spores.
Although removal of infected plant material and debris can reduce the source of inoculum in the field, regular fungicide applications are typically necessary for managing botrytis fruit rot. Since fruiting occurs continuously for several months and fungicides are regularly applied, botrytis resistance to fungicides is not uncommon. Applying fungicides only when necessary, avoiding continuous use of fungicides from the same mode of action group and exploring the potential of biological fungicides to reduce the risk of resistance development are some of the strategies for effective botrytis fruit rot management. In addition to several synthetic fungicides, several biological fungicides continue to be introduced into the market offering various options for the growers. Earlier field studies evaluated the potential of various biological fungicides and strategies for using them with synthetic fungicides against botrytis and other fruit rots in strawberry (Dara 2019; Dara 2020). This study was conducted to evaluate some new and soon-to-be-released fungicides in fall-planted strawberry to support growers and ag input industry, and to promote sustainable disease management through biological and synthetic pesticides.
Methodology
This study was conducted on a conventional strawberry field at Manzanita Berry Farms, Santa Maria in strawberry variety 3024 planted in October 2020. Treatments included fungicides containing captan and cyprodinil + fludioxinil as synthetic standards along with a variety of biological fungicides of microbial, botanical and animal sources at various rates and different combinations and rotations. Products and active ingredients evaluated in this study included captan 38.75%, cyprodinil 37.5% + fludioxinil 25%, potassium carbonate 58.04% + thyme oil 1.75%, botanical extract 100 g AI/L, giant knotweed extract 5%, protein 15-20%, cinnamon oil 15% + garlic oil 20%, caprylic acid 41.7% + capric acid 28.3%, Pseudomonas chlororaphis strain AFS009 50%, Bacillus subtilis strain AFS032321 100%, P. chlororaphis strain AFS009 44.5% + azoxystrobin 5.75%, Banda de Lupinus albus doce – BLAD (a polypeptide from sweet lupine) 20% with chitosan 2.3% or pinene (polyterpenes) polymers, petrolatum, alkyl amine ethxylate (spreader/sticker) 100%, thyme oil 20% and a thyme oil blend.
Although removal of infected plant material and debris can reduce the source of inoculum in the field, regular fungicide applications are typically necessary for managing botrytis fruit rot (all photos by S.K. Dara.)
Excluding the untreated control, the rest of the 24 treatments can be divided into synthetic fungicides, a fungicide with synthetic + biological active ingredients (a formulation with two application rates), synthetic fungicides alternated with biological fungicides and various kinds of biological fungicides (Table 1). Treatments were applied at a 7- to 10-day interval between April 22 and May 17, 2021. Berries for pre-treatment disease evaluation were harvested on April 19, 2021. Each treatment had a 5.67’ x 15’ plot replicated four times in a randomized complete block design. Strawberries were harvested three days before the first treatment and three to four days after each treatment for disease evaluation. On each sampling date, marketable berries were harvested from random plants within each plot during a 30-second period and incubated in paper bags at outdoor temperatures under shade. Number of berries with botrytis infection were counted on three and five days after harvest (DAH) and percent infection was calculated. This is a different protocol than previous years’ studies where disease rating was made on a 0 to 4 scale. Treatments were applied with a backpack sprayer equipped with hollow cone nozzle using 90 gpa spray volume at 45 PSI. Water was sprayed in the untreated control plots. A surfactant with methyl esters of C16-C18 fatty acids was used at 0.125% for treatments that contained protein P. chlororaphis alone and in combination with azoxystrobin, B. subtilis, thyme oil and thyme oil blend. Research authorization was obtained for some products and crop destruction was implemented for products that did not have California registration.
Percent infection data were arcsine-transformed before subjecting to the analysis of variance using Statistix software. Significant means were separated using the least significant difference test.
Results
Pre-treatment infection was very low and occurred only in some treatments with no statistical difference (P > 0.05). Infection levels increased for the rest of the study period. There was no statistically significant difference (P > 0.05) among treatments for disease levels three or five days after the first spray application. Differences were significant (P = 0.0131) in disease five DAH after the second spray application where 13 treatments from all categories had significantly lower infection than the untreated control. After the third spray application, infection levels were significantly lower in eight treatments in three DAH observations (P = 0.0395) and 10 treatments in five DAH observations (P = 0.0005) compared to the untreated control. There were no statistical differences (P > 0.05) among treatments for observations after the fourth spray application or for the average of four applications. However, there were numerical differences where infection levels were lower in several treatments than in untreated control plots.
In general, the efficacy of both synthetic and biological fungicides varied throughout the study period among the treatments. When the average for post-treatment observations was considered, infection was numerically lower in all treatments regardless of the fungicide category. Since the rates, rotations, and combinations were all experimental, additional studies can help determine optimal use strategies for these active ingredients. Multiple biological fungicide treatments either alone or in rotation with synthetic fungicides appeared to be as effective as synthetic fungicides. These biological fungicides can be an important part of integrated disease management, especially for the botrytis fruit rot that has frequent resistance problems.
Thanks to AgBiome, AgroSpheres, Biotalys, NovaSource, Sym-Agro, Syngenta, and Westbridge for funding and Chris Martinez for his technical assistance.
References Dara, S. K. 2019. Five shades of gray mold control in strawberry: evaluating chemical, organic oil, botanical, bacterial, and fungal active ingredients. UCANR eJournal of Entomology and Biologicals. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=30729 Dara, S. K. 2020. Evaluating biological fungicides against botrytis and other fruit rots in strawberry. UCANR eJournal of Entomology and Biologicals. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=43633 Williamson, B., B. Tudzynski, P. Tudzynski, and J.A.L. van Kan. 2007. Botrytis cinerea: the cause of grey mold disease. Mol. Plant Pathol. 8: 561-580.
BetterSoil Alliance Rewards Growers for Sustainable Achievements
Yara and Heliae® Ag invite the almond industry to join them in driving practical solutions that positively impact food production by improving water productivity and soil health
TAMPA, Fl. (Oct 18, 2021) – Yara North America, Inc. with Heliae® Agriculture, has launched the BetterSoil Alliance to support the California almond industry in the pursuit of sustainable farming practices to improve water productivity and soil health, while decreasing their carbon footprint. Through the Alliance, sustainably-focused solutions will be put to the test to understand their collective impact on critical issues the almond industry faces including water scarcity, drought and rising temperatures; all which are challenging the long-term viability of the almond industry.
Almond growers and advisors are invited to participate in implementing the solutions through customized crop and soil nutrition programs that will be developed by mid-November. Participants will be eligible to receive a sustainability reward based on water productivity and nitrogen use efficiency (NUE), as well as recognition in the Alliance. Data collected from participating growers’ orchards will be used to better understand the positive impact the solutions implemented in the program can have. Yara North America, Inc. and Heliae® Agriculture will help fund a portion of the sustainability rewards, however to acknowledge as many growers as possible, the companies are calling on the industry to participate through pledges to help fund the sustainability awards.
“To support the longevity of the California almond industry we are focused on bringing practical solutions that positively impact food production by improving water use productivity and soil health” said Debbie Watts, VP Yara North America. “We know by collaborating with others across the industry; growers, advisors, hullers, processors and food companies for instance, we can achieve more. This is why we have launched the BetterSoil Alliance, with the belief that industry partners will come together and accelerate building out sustainable solutions through discovery and collaboration to address this urgent need.”
Participating growers and advisors will have access to the agronomic expertise of Yara North America, Inc. and Heliae® Agriculture. Additionally, they will receive support in implementing crop nutrition and soil management solutions that include YaraLiva® Calcium Nitrate; produced in Norway and featuring a very low carbon footprint, and PhycoTerra® a superior, nature-based soil microbial food, specifically produced to feed the dormant microbes-including fungi and bacteria. Yara North America, Inc. and Heliae® Agriculture hope the program will help demonstrate these products together synergistically drive almond yield and quality, while improving soil health and structure. Moreover, independent third-party trials show a measurable improvement in water productivity (crop per drop) when YaraLiva® Calcium Nitrate and PhycoTerra® products are used in tandem.
“Improving soil quality serves as the foundation to improving water use that help optimize crop yield and quality”, said Norm Davy, Heliae® Agriculture. “Between the increased consumer demand for almonds and tightening water supply in California, growers need solutions that increase yield and improve soil health and soil structure for future crops.”
To learn more about the BetterSoil Alliance and how you can get involved, visit www.yara.us/bettersoil/.
About Yara
Yara grows knowledge to responsibly feed the world and protect the planet. Supporting our vision of a world without hunger and a planet respected, we pursue a strategy of sustainable value growth, promoting climate-friendly crop nutrition and zero-emission energy solutions. Yara’s ambition is focused on growing a climate positive food future that creates value for our customers, shareholders and society at large and delivers a more sustainable food value chain.
To achieve our ambition, we have taken the lead in developing digital farming tools for precision farming, and work closely with partners throughout the food value chain to improve the efficiency and sustainability of food production. Through our focus on clean ammonia production, we aim to enable the hydrogen economy, driving a green transition of shipping, fertilizer production and other energy intensive industries.
Founded in 1905 to solve the emerging famine in Europe, Yara has established a unique position as the industry’s only global crop nutrition company. We operate an integrated business model with around 17,000 employees and operations in over 60 countries, with a proven track record of strong returns. In 2020, Yara reported revenues of USD 11.6 billion. To learn more visit www.Yara.US.
About Heliae® Agriculture
Heliae® Agriculture, a division of Heliae Development LLC, provides innovative microalgal products to the agricultural community. Dedicated experts in the soil and crop science fields, Heliae® Agriculture is focused on delivering regenerative agriculture solutions with its PhycoTerra® product portfolio. PhycoTerra® branded products are sourced from nature and work to improve overall soil microbial health, structure, water productivity, and nutrient use efficiency, which helps to increase crop yields sustainably for the planet, farmers, and consumers. Learn more about how PhycoTerra®’s pasteurized microalgal products will help achieve your regenerative agriculture objectives at www.phycoterra.com.
Increase yield potential and maintain a healthy orchard by selecting the right crop protection solutions for your unique needs. Prevent disease, eradicate tough weeds and control insects with branded-generic fungicides, herbicides and insecticides from Atticus. Explore the broad and expanding tree nut product portfolio for season-long protection. Learn more at Atticusllc.com
To keep the pathogen from spreading to infected fields, Bolda recommended minimizing movement of soil from field to field on shoes and equipment (photo courtesy Joji Muramoto.)
Wilt disease in strawberries caused by the pathogen Fusarium oxysporum forma speciales fragariae is expanding quickly and merits attention from strawberry growers.
Mark Bolda, UCCE strawberry and caneberry farm advisor in Santa Cruz County, emphasized that fumigation operations in infected fields are worth the cost even when using plants resistant to this pathogen. Speaking at the 2021 Crop Consultant Conference, Bolda also noted that crop termination works to improve yields in resistant varieties through the season and in the first half of the season in susceptible varieties.
“Crop termination very much looks like it enhances chloropicrin efficacy in susceptible varieties,” Bolda said.
The majority of the genus Fusarium oxysporum is not pathogenic and is common in soil and around roots. Individual types are specific to host plants. This pathogen does grow on other field crops, but does not thrive, except on strawberries. Infected plants become noticeable from May to June as crowns split and become discolored. Bolda said 80% of the disease load is in the crown of the plant.
Bolda said Fusarium in strawberry could possibly coincide with the reduction and prohibition of methyl bromide. When many plants are diseased at once in a field, that does not necessarily mean the disease came with the transplants. This specific pathogen does not show symptoms at low levels and can augment populations over several successive crops of strawberries. Management of this pathogen consists of sanitation, fumigation, crop rotation and possibly fungicide applications.
He advised minimizing movement of soil from field to field on shoes and equipment to keep from spreading the pathogen to uninfected fields. Crop rotation is at least 18 months before returning to strawberries. The longer the better, Bolda said.
Bolda’s field trial set out to test efficacy of fumigant treatments and crop rotations against the strawberry-specific Fusarium pathogen. Treatments tested were KPAM at 20 gallons per acre and crop termination, Dominus at 20 gallons per acres, Tri Clor 80 at 350 pounds per acre and KPAM drip at 47 gallons per acre. Varieties were Fusarium-resistant San Andreas, Fusarium-susceptible Monterey and Fusarium-resistant Fronteras. Dominus, Bolda noted, is close to being registered in California.
All of the treatments showed significantly higher crop yields in Monterey from April through August compared to the untreated control. The treatment of KPAM plus crop termination then Tri Clor 80 had the highest yields.
The invasive vine mealybug is the most problematic of all mealybug species and causes the most damage in California vineyards (photo by Jack Kelly Clark, UC Statewide IPM program.)
New insecticides, new combinations of insecticides, biological controls and improved mating disruption to control vine mealybug (VMB) are all under study, but costs and necessary control levels are issues, said UCCE Assistant Specialist Kent Daane.
The invasive vine mealybug is the most problematic of all mealybug species and causes the most damage in California vineyards. Damage by the vine mealybug is similar to that of other grape-infesting mealybugs in that it produces honeydew that drops onto the bunches and other vine parts and serves as a substrate for black sooty mold. Mealybugs also will infest grape clusters. Vine mealybug can vector grapevine leafroll associated viruses which have been associated with sudden vine death.
During dormancy and early spring, VMB are found primarily on the trunk, canes and roots, but this can vary by vineyard location. In the spring, VMB moves onto canes and later onto leaves. In the summer, VMB moves into grape clusters. The trunk and the bark of canes provide refuge from insecticides, including systemics and natural enemies.
Ants can be a sign of a VMB infestation. Daane said that ants give refuge to VMB and also improve their habitat by removing honeydew. This tending by ants, increases VMB populations.
Bark wetness is a sign of a mealybug infestation as honeydew production increases. Leaf drop in June can also be sign of an infestation. If a VMB infestation is suspected, crowns and trunks can be inspected in the spring for adult females and crawlers. Starting at bloom, cordons, canes and basal leaves should be inspected. When fruit is present, clusters can be scouted for signs of VMB. Pheromone traps in vineyards from August to October can give record of VMB numbers and indicate numbers for next season. Daane warned that it is common to have high trap counts with little actual crop damage.
Increasing resistance to chemistries used in the past to control VMB make it important to rotate those chemistries which are still effective. Daane said there are both conventional and OMRI-approved insecticides to control VMB, but none provide 100% control.
“Movento is the best, but we are seeing cracks in control,” he warned.
Use of mating disruption devices in the vineyard can help with control. They work best with low VMB pressure. Daane said the effect is better in the second or third year. Ants also must be controlled.
The proposal for application notification has been unknowns, including who will be notified of a planned pesticide application, when and how will they be notified, and what products and application methods are regulated.
The California Department of Pesticide Regulation (CDPR) is in the process of developing a statewide pesticide application notification system. Roger Isom, president of Western Agricultural Processors Association, participated in a DPR focus group session in August and reported on this issue at the 2021 Crop Consultant Conference.
Input from the agriculture industry on this proposal to require notification of a pesticide application is vital, said Isom. He urged all growers and PCAs to voice their concerns about the draft proposal to CDPR. Public webinars on the proposal are being held this month. Isom said the draft regulation would be announced in spring 2022.
Unknown at this time are the questions of who will be notified of a planned pesticide application, when will they be notified, how do they get notified, what products are covered and what application methods are covered.
At this time, it is only a proposal, and details are not decided, but Isom warned that the governor has indicated that notification is a priority for him and $10 million has been directed to develop the proposal.
Isom said this action was triggered by Assembly Bill 617 and an air quality reading in Shafter in Kern County that measured 1,3-D; however, there was no known application within seven miles of the measurement. AB 617, signed by Governor Newsom in 2017, establishes a community-scale emissions abatement program and updates air quality standards for sources that contribute to poor air quality.
Isom pointed out that only three states have some type of notification system for pest control applications: Florida, Maine and Michigan. Monterey County has a program for fumigation application notifications for schools. The public is eligible for notification and it is done five days prior to a fumigation. Currently in Kern County, notification is only for restricted use materials and is only required to growers in surrounding areas of the planned application.
Isom noted that in some instances, anyone is able to sign up for notifications, and in the past, it was found that the majority of those requesting notification did not live in the area of the application. In Florida, those requesting notification must be on adjacent or contiguous property up to a half mile.
Isom said any form of this rule should be statewide, reasonable and justification for those asking to be notified of a pesticide application. Public webinars are being held this month. Written comments can be submitted to CDPR.
Potential for mold development in a walnut crop increases as harvest is delayed. Sunburnt nuts, windfalls on the ground for more than 15 days, nuts infested with navel orangeworm, nuts with large stem openings and larger nuts are subject to mold development (photo by C. Parsons.)
UC Davis Plant Pathologist Themis Michailides reported recent research findings on walnut mold and management at the 2021 Crop Consultant Conference.
The main pathogens of walnut mold are Alternaria, Fusarium species and Aspergillus niger. Botryosphaeria and/or Phomopsis canker and the bacterial disease walnut blight are also cause for mold in orchards.
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Brown Apical Necrosis is a special type of walnut mold that always starts from the stylar end of the nut and is sometimes associated with the bacterial disease walnut blight. Michailides confirmed that there is a strong correlation of fungi causing walnut mold with the same fungi attacking and decaying the hulls. The incidence of mold starting from the stylar end was significantly greater than that of mold starting from the stem end, suggesting possible stylar infection at bloom. In trials over two years, sprays at two to three weeks before hull split and early hull split reduced walnut mold in both early and late walnut cultivars.
In the U.S. standards for grades of walnuts, mold is listed as damage when attached to the kernel or when white or gray mold affects a portion of the surface of the kernel. Potential for mold development in a walnut crop increases as harvest is delayed. Sunburnt nuts, windfalls on the ground for more than 15 days, nuts infested with navel orangeworm, nuts with large stem openings and larger nuts are also subject to mold development.
Michailides said levels of mold reported in recent years included a Chandler sample from Tulare County showing 21% mold, grade sheets from 2020 from Butte County areas near the Sacramento River with 10% to 16% mold and, in 2019, reports of 10% to 20% mold in Butte and Glenn counties.
In his presentation, Michailides noted that previous studies on walnut mold showed that mid-May to mid-July sprays reduced Botryosphaeria and Phomopsis canker and blight, but they did not reduce molds caused by Alternaria or Fusarium. He said the fact that fungi-causing mold are the same as those that colonize the hulls led the decision to move towards sprays before hull split and early hull split.
To reduce incidence of mold in walnuts, Michailides said applying Merivon at three weeks prior to hull split reduces mold related to Botryosphaeria, Phomopsis and Alternaria. Adding Tebuconizole to the tank mix will increase efficacy against Phomopsis. To further increase efficacy, apply Rhyme at 20% to 30% hull split. If the high level of control is not needed, Rhyme can be applied at 20% to 30% hull split.
West Coast Nut magazine is offering California tree nut growers a rare opportunity to network across the industry at the second annual California Tree Nut Conference in Tulare Nov. 3. In addition to the usual continuing education seminars and industry trade show, growers attending this year’s free event will hear from California Agriculture Secretary Karen Ross, who will discuss priorities for the California Department of Food and Agriculture and how the agency will support nut growers in meeting those priorities.
In addition, growers will interact with commodity board leaders for the state’s top nut crops in a leadership panel titled “Where Are We Heading?” Panelists will include Michelle Connelly, executive director and CEO of the California Walnut Board and Commission, Richard Waycott, CEO of the Almond Board of California, Richard Matoian, CEO of American Pistachio Growers, and Mark Hendrixson, director of the California Pecan Growers Association.
“Given the many challenges nut growers have faced over the last year, we are using our conference to address big-
picture issues that impact the bottom line for nut growers in California,” said Jason Scott, Publisher of West Coast Nut magazine. “At the same time, we understand that continuing education and networking opportunities with industry suppliers are also important, and we have plenty of that as well.”
A morning panel on “Irrigation Technology and Automating Monitoring Systems in Tree Nut Crops” will feature UC Davis irrigation experts Ken Shackel and Isaya Kisekka, as well as industry suppliers, growers and consultants. They will discuss existing and emerging technologies to determine soil and plant water status for data-driven irrigation management in nut crops.
After the trade show break and post-harvest nutrition demonstration, CEU talks related to nematode management and new technology for monitoring and managing nut pests will be featured. The California Tree Nut Conference will be held from 7 a.m. to 1 p.m. at the Tulare County Fairgrounds in Tulare. Registration is free and can be done online at WCNGG.com or by calling the JCS Marketing office at (559) 352-4456.
