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Grapevine Water and Nutrient Management Tips During Drought

The San Joaquin Valley (SJV) is in the midst of an ongoing drought. Total precipitation in Fresno from October to March was 7.3 inches which amounts to 60% of the historical average of 12 inches. With little or no rain in the forecast and in anticipation of another dry and hot summer, growers might reflect on some environment-related issues observed in 2021.

Figure 1. Precipitation, irrigation hours and soil moisture content (volumetric) at a soil depth of two feet from May 2021 to March 2022.

Maintaining Adequate Soil Moisture is Critical
Many growers who suffered greatly from delayed spring growth (DSG) in 2021 allowed the soil to become too dry the preceding fall or winter. Sufficient carbohydrate content of the vines and adequate soil moisture are the keys to dodge DSG. Healthy carbohydrate content in the vines can be attained with a balanced canopy vs yield and a pest-free canopy kept in good condition postharvest. Adequate soil moisture can be achieved through postharvest irrigation or even winter irrigation if precipitation is lacking. Postharvest irrigation helps prevent early defoliation, reduces the chance of winter freeze damage, helps leach any accumulated salts and helps rehydrate the vines after they emerge from dormancy.
Thus, a key lesson learned from 2021 should be the importance of maintaining soil moisture during the winter months. The beginning of last winter saw record precipitation, and many growers took proactive measures to prevent DSG in the dry second half of winter in early 2022. For example, in Figure 1, postharvest irrigation (end of September), winter irrigation (mid-November) and early spring irrigation (mid-February) have been noticed from this vineyard, which is one of the collaborative sites contributing to the UC IPM weather station networks (ipm.ucanr.edu/weather/grape-powdery-mildew-risk-assessment-index). As a pilot study site, we added a pressure switch and soil moisture probes at soil depth of 1, 2 and 3 feet to help growers improve their irrigation scheduling. We are glad to see growers are taking advantage of those data to manage vineyard water to reduce the risk of DSG.
Ideally, a regional soil moisture content network could provide critical winter soil moisture information to guide growers near the station to decide whether to irrigate the vines during the winter month.

Figure 2. Monthly max ambient temperature between 2021 and last 20 years’ average. Data are collected from CIMIS Station #80 at Fresno State.

Cultural Practices Can Help Protect Against Heatwaves
Besides the severe winter drought, growers also experienced record summer heat in 2021. Max monthly temperature in 2021 was much higher than last 20 years’ average, especially in June and July (Figure 2), and monthly reference evapotranspiration (ETo) in 2021 was also higher than the last 20 years’ average (Figure 3). Sun-exposed clusters and berries under the extreme summer heat will develop sunburn, which will reduce fruit yield and quality, including Brix and raisin B&B grade. I have written a previous article about grapevine heat stress and sunburn management (Progressive Crop Consultant May/June 2019), and many tools are available for growers:

  • When developing a new vineyard, row orientation and trellis design can help minimize direct sun exposure to fruit.
  • Canopy management practices, such as shoot tucking, can help minimize the direct sun exposure to fruits.
  • Sunblock sprays, such as Kaolin and CaCO3, increase reflectance and thereby reduce solar heating of fruit and leaves.
  • Evaporative cooling, such as in-canopy micromisting, can be effective, but water use and disease pressure could be increased.
  • Last but not least, adequate irrigation to develop the canopy which can help shade the fruit and protect fruits.

Among all the above options, irrigation might be the most important to prevent fruit sunburn during heat waves, since the sufficient canopy promoted by irrigation does not only serve as the photosynthetic machinery to produce carbohydrate to ripen fruits, but also provides the shade for fruits to reduce excessive sun exposure. There are many irrigation tools which growers can use to watch out for potential water deficit in their vineyards:

  • Soil moisture-based irrigation.
  • Plant water-based irrigation.
  • Weather-based irrigation.
Figure 3. Monthly ETo between 2021 and last 20 years’ average. Data are collected from CIMIS Station #80 at Fresno State.

Most growers I have talked to have soil moisture sensors on-site, and currently, CDFA offers various grants (cdfa.ca.gov/oefi/sweep/) to help growers install soil moisture sensors.
No matter which soil moisture sensor you have, the key is to identify the soil moisture benchmark which you can target the irrigation to. So, how can soil moisture sensors help you to target the benchmark and manage the water in your vineyard? For example, based on Figure 1 (see page 26), from May 2021 to August 2021, growers utilized the soil moisture sensor (soil water volumetric sensor, Campbell Scientific CS655) to schedule the irrigation to maintain the soil moisture content range from 10% to 15% at soil depth of two feet.
On this site, three soil water volumetric sensors were installed at approximately one foot from the vine trunk and six inches from the emitter. Sensors were set at the depth of one, two and three feet beneath the soil surface. We assume growers are satisfied with the canopy and crop development during the season, and a field study done by Dr. Larry Williams at UC Kearney REC also shows 10% to 15% soil moisture content correlates to -1.2 to -0.9 MPa midday leaf water potential (Williams 2012). The range from -1.2 to -0.9 MPa of midday leaf water potential is regarded as mild water stress or no water stress for the SJV vines and can be used to maximize the crop production (Figure 4).
Given the soil type on this site is similar to the Hanford fine sandy loam soil in UC Kearney REC, the same range of soil moisture content can serve as a good benchmark for any future irrigation scheduling on this site. Please note that no water applied after mid-August aimed to prepare the soil for raisin drying. Unsurprisingly, in 2022, growers started the early spring irrigation in mid-February to target the same range of soil moisture content from 10% to 15% to prepare the budbreak and early shoot development. Therefore, growers can irrigate the grapevines by selecting the desired soil moisture benchmark based on the preferred canopy and crop development on your specific soil type.

Figure 4. The relationship between midday leaf water potential measured on Thompson Seedless grapevines and soil water content (SWC, measured as the percent of volume). At the study site of UC Kearney REC, the soil type is Hanford fine sandy loam and 10% to 15% SWC correlates to -1.2 to -0.9 MPa midday leaf water potential, which is regarded as mild water stress or no water stress for the SJV grapevines.

Nutrient Management During Drought
Low rainfall in autumn to midwinter can cause drought-induced boron deficiency. The symptoms are erratic budbreak, stunted and distorted shoots, misshapen and chlorotic leaves. The most classic symptoms after budbreak are dwarfed shoots that grow in a zigzag manner with numerous lateral shoots, and the tip of the primary shoot may die. Most shoots begin to elongate normally by late spring, but cluster size may be reduced. The cause is believed to be a late-season drought-induced boron deficiency that affects development of shoots within dormant buds.
The key to reduce drought-induced boron deficiency is postharvest irrigation. Traditionally, Thompson raisin vineyards go through the harvest and raisin-drying processes for a nearly two-month period without irrigation (Figure 1, see page 26). The postharvest irrigation can relieve the water stress and maintain a healthy functional canopy to avoid boron deficiency.
Spring fever is sometimes referred to as false potassium deficiency because the leaf symptoms resemble and are sometimes confused with potassium deficiency. Alternating warm and cold weather patterns before bloom, as has been observed this spring, can cause a temporary nitrogen metabolism disorder associated with high levels of ammonium and the polyamine putrescine in the leaves.
Symptoms occur in basal leaves and leaves in the fruit zone. Lower leaf color fades and becomes chlorotic in spring, beginning at the leaf margins and progressing between the primary and secondary veins. Leaf margins may become slightly necrotic, marginal necrosis is significant and affected leaves can drop.
There is no cure for spring fever, and petiole/blade laboratory analysis can differentiate true K deficiency from spring fever. Spring fever typically will fade as the weather warms up and the onset of symptomatic leaves decreases around bloom; however, blades with existing symptoms will remain.

Spring fever in basal leaves of Thompson Seedless, showing chlorosis, curling and browning of leaf margins.

References
Bettiga, Larry. Grape Pest Management, Third Edition. University of California Agriculture and Natural Resources. 2013.
Christensen, Pete. Raisin Production Manual. University of California Agriculture and Natural Resources. 2000.
Williams, L. (2012), Effects of applied water amounts at various fractions of evapotranspiration (ETc) on leaf gas exchange of Thompson Seedless grapevines. Australian Journal of Grape and Wine Research, 18: 100-108. https://doi.org/10.1111/j.1755-0238.2011.00176.x

Mating Disruption of California Red Scale in Citrus

California red scale, Aonidiella aurantii, is one of the primary insect pests of citrus crops in California and other states where commercial citrus is grown. Originally native to southeast Asia, it is believed to have arrived in California between 1868 and 1875 and is now distributed worldwide. California red scale (CRS) is a cosmetic pest of fruit that can result in costly economic damage due to downgrades at the packinghouse. In addition, infestations of leaves, twigs and branches can cause overall negative impacts to plant health. As a result, reliance on insecticides has been historically necessary to mitigate damage caused by this pest.
During the last half of the 20th century, CRS control relied on the use of broad-spectrum insecticides in the carbamate and organophosphate classes. By the late 1990s, these chemistries were no longer effective in many orchards due to the development of insecticide resistance. In the early 2000s, additional chemistries came to the market and proved valuable to aid in managing CRS. These newer-generation insecticides, based on insect growth regulators, proved effective for several years.

Adult female California red scale. Adult females are sessile and attached to the plant surface (photo courtesy UC Statewide IPM Program.)

Unfortunately, there were still a limited number of insecticide modes of action available for control, and by 2006, resistance to one of the primary insect growth regulators (pyriproxyfen) was confirmed in CRS populations in the Central Valley of California. An integrated pest management approach is necessary to maintain effective control of CRS and extend the lifespan of the remaining available insecticide chemistries.
The foundation of integrated pest management (IPM) programs for CRS includes biological control, cultural practices and judicious use of selective insecticides as needed based on monitoring and treatment thresholds. There are effective biological control agents for CRS, including multiple parasitic wasps and general predators. Unfortunately, necessary insecticide applications for the invasive Asian citrus psyllid have reduced the impacts of these natural enemies. More recently, mating disruption has emerged as a fundamental component of successful IPM programs and does not adversely affect natural enemies. Incorporating each of these IPM approaches will benefit growers by reducing crop damage and mitigating further insecticide resistance development.

California red scale male and female mating. Males are extremely short-lived as adults, living approximately six hours, and their only purpose is to locate females for reproduction (photo courtesy UC Statewide IPM Program.)

California Red Scale Biology
California red scale typically has four to six generations each year in California depending on growing region and environmental factors. Adult females are sessile and attached to the plant surface, and each produces on average 100 to 150 crawlers. The crawlers are mobile, however longer distance dispersal of crawlers is often due to wind, birds, equipment, or orchard workers. Adult males are the only life stage with wings and capable of flight. Males are extremely short-lived as adults, living approximately six hours, and their only purpose is to locate females for reproduction. Mate location is facilitated by a sex pheromone emitted by adult female scales.

California red scale crawlers. Crawlers are mobile, however longer distance dispersal of crawlers is often due to wind, birds, equipment, or orchard workers (photo courtesy UC Statewide IPM Program.)

Mating Disruption for CRS
Mating disruption for CRS is a technology that utilizes the insect’s sex pheromone as a management tactic to interfere with the ability of males to locate females for reproduction, thereby reducing pest populations and crop damage. This technology has been commercially available in California since 2016, and adoption is increasing each year as positive benefits are observed.
A recent publication by leading University citrus researchers summarized a multi-year study demonstrating the efficacy and value of CRS mating disruption in California’s Central Valley citrus production. These studies used the commercially available CRS mating disruption product CheckMate CRS dispensers at the label rate of 180 dispensers/acre. The research team, led by University of California citrus specialist Elizabeth Grafton-Cardwell, concluded several key findings as a result of their 2016-19 studies in 12 commercial citrus orchards.
Significant reductions in pheromone trap capture, twig and leaf infestations and infested fruit were consistently demonstrated where CRS mating disruption was applied compared to non-mating disruption reference plots. Suppression of male capture in pheromone traps, an indicator of effective mating disruption, averaged 90%. Twig and leaf infestations were reduced by an average of 75%, and the percentage of highly infested fruit at harvest was less than 0.5% in 9 of the 10 mating disruption blocks in 2018 and 2019.
Summary conclusions within the publication state, “mating disruption using CheckMate CRS can be an effective method to reduce California red scale populations throughout the four-plus generations that occur in central California,” adding that “mating disruption has the potential to reduce or eliminate pesticide applications.” It is important to note that the decision to reduce or eliminate any inputs in the overall IPM program should be determined on an individual basis based on grower and crop adviser consultation.

Adult male California red scale. The dark band is a key feature for identification (photo courtesy UC Statewide IPM Program.)

Implementing CRS Mating Disruption
In general, there are three primary types of mating disruption products or delivery methods. These include vapor dispensers (also called passive dispensers), aerosols and sprayable microencapsulated formulations. The type of delivery method or product that is most effective for a given pest will be based on the pest’s biology and flight behavior as well as the architecture of the cropping systems (i.e., orchard, vineyard or field canopy structure). For example, aerosol-style mating disruption products have been used for many Lepidopteran pests, including codling moth and navel orangeworm in orchard crops for several years. Vineyard crop systems are effectively battling vine mealybug with sprayable formulations or vapor dispensers. Vapor dispensers have also been particularly effective in citrus crop systems to reduce California red scale.
The distribution of very small pests, like CRS, is often aggregated in the environment with distinct hotspots. Males are not strong fliers and tend to stay within the tree canopy when searching for mates. This is different from moths, which are stronger fliers and spend more time flying within the orchard rows in search of mates. Because of this, the current high-density vapor dispenser is the most effective pheromone delivery method for disrupting mating of CRS. Aerosols in their current configurations, which are highly effective for moths, are not as effective for pests like California red scale and vine mealybug (VMB) because of these biological and behavioral differences. Sprayable microencapsulated formulations can be thought of as billions of microscopic dispensers and are therefore also effective mating disruption delivery systems for pests like CRS and VMB.
California red scale mating disruption with CheckMate CRS is designed to consistently permeate the orchard environment with the insect’s sex pheromone precisely within the tree canopy where the pests are located. They are applied at a rate of 180 per acre by hand from the ground. Because of pest biology and where populations are most abundant, dispensers should be placed within the tree canopy and not on outer branches. Deployment patterns are based on row and tree spacing and total number of trees per acre.
Common row and tree spacing patterns are available on the manufacturer website (Suterra.com) and the manufacturer field team is available to assist with designing dispenser patterns for orchards with other spacings. When possible, dispensers should be placed after pruning, or if before, care taken not to prune out the current season’s mating disruption dispensers. The controlled release of pheromone lasts a full calendar year. Therefore, precise deployment timing is not critical. Many users choose to re-apply their CRS mating disruption dispensers before the historical first or second flights each year.

California red scale mating disruption vapor dispensers are designed to consistently permeate the orchard environment with the insect’s sex pheromone precisely within the tree canopy where the pests are located (photo courtesy Suterra.)

Benefits of Mating Disruption in the Overall IPM Program
In addition to the validated efficacy in reducing CRS populations and damage, incorporating mating disruption into the overall IPM program for any pest provides additional benefits. Pheromone mating disruption is non-toxic; it does not kill anything.
Its efficacy is based on interfering with reproduction, thereby preventing significant portions of subsequent generations from ever existing. This allows all other inputs (cultural, biological, chemical) to have greater impact, simply because there are fewer individuals to have to kill or remove from the environment. This technology is safe for non-target species (natural enemies, pollinators, humans) and is MRL exempt.
Mating disruption is not subject to resistance development and may help delay insecticide resistance due to reductions in the number of insecticide applications needed for effective CRS control. Dispenser-based mating disruption for CRS has zero re-entry interval, zero pre-harvest interval and is approved for use in organic agricultural production.

References
Grafton-Cardwell, E. E., J. T. Leonard, M. P Daugherty, and D. H. Headrick. 2021. Mating Disruption of the California Red Scale, Aonidiella aurantii (Hemiptera: Diaspididae) in Central California Citrus. Journal of Economic Entomology 114(6): 2421-2429.

Mechanization Improves Pruning Efficiency in Table Grape Vineyards

Mechanization is clearly one of the best solutions to reduce labor requirements for vineyard management and lower production cost. Even though pruning machines are extensively used in wine grapes grown in the San Joaquin Valley, the mechanization of pruning in table grapes remains challenging.
Most of the table grape vineyards grown in the San Joaquin Valley use a “Y” trellis system (open Gable system). This highly structured trellis provides adequate support to large canopies of table grapevines but limits the options of mechanization. In addition, table grapes have high aesthetic requirements. Growers rely on vineyard crews to adjust the location and numbers of spurs and canes at pruning to maintain vine shape and achieve desirable yield and fruit quality. In this regard, mechanical tools that are currently available cannot mechanize the entire pruning process in table grape vineyards. However, mechanizing part of the process is possible.
Cane pruning, spur pruning and spur pruning with kicker canes are used in table grape vineyards, and the choice of method is based on basal bud fruitfulness of specific varieties and growers’ preferences. Despite the difference in pruning methods, there are three general steps involved, including 1) selecting canes and cutting canes to desirable length; 2) pulling pruned canes off the catching wires and placing them between rows; and 3) tying canes or new cordons to the wire.
Mechanization has the potential to improve efficiency in the latter two steps. Andros Wye trellis pre-pruner (Andros pre-pruner) snaps canes and removes part of the wood materials before workers cut canes to spurs (Figure 1). KLIMA cane pruning system (KLIMA shredder) strips canes from the wires and mulches them after an initial pass of cutting canes (Figure 2). Battery-powered shears are alternatives to conventional hand shears, expected to reduce the fatigue of workers and lower the risk of repetitive motion injuries (Figure 3). Battery-powered tying machines simplify the tying process and may reduce the time needed to tie individual canes.
Despite the promising outlook of mechanical pruning tools, more evaluation is needed on their suitability in different training systems and whether mechanization can decrease labor requirements for pruning. Thus, as supported by the California Table Grape Commission, we evaluated those four mechanical pruning tools in four different table grape vineyards in 2022 between January and March.

Figure 2. KLIMA cane shredder in a spur-pruned vineyard. The machine strips canes from the wires and mulches them after an initial pass of cutting canes.

KLIMA Cane Pruning System
We evaluated the KLIMA shredder in a spur-pruned ‘Holiday’ vineyard and a cane-pruned ‘Autumn King’ vineyard. Self-releasing clips were installed on the “V” cross arms in both vineyards prior to the evaluation (Figure 4). Those clips allow the shredder to directly pull catching wires from cross arms without human assistance. In each vineyard, 7 to 10 continuous rows were hand-pruned, and the adjacent 7 to 10 rows were pruned using the adjusted procedure.
On the first day, workers cut canes to desirable lengths without pulling pruned canes off the wire. On the second day, the KLIMA shredder was hooked to a tractor for passes in the vineyard. In each pass, the shredder caught the catching wires, releasing them from crossarms, stripped canes from the wires and mulched those canes. A worker was assigned to guide the tractor driver. The time required for shredding ranged between 1.5 and 2 hours per acre. On the third day, workers replaced catching wires back to crossarms.
When the KLIMA shredder was used, the non-machine labor hours required to prune vines reduced by 26% to 34% (Table 1), leading to a savings of $150 to $200 per acre on labor costs. A greater reduction in labor requirement was observed in the spur-pruned vineyard than in the cane-pruned vineyard. It seems the KLIMA shredder conveys a greater benefit in vineyards where pulling canes off the wire takes similar or more time than cutting canes. Indeed, we found that workers spent a similar amount of time on cutting and pulling canes in the spur-pruned vineyard. In the cane-pruned vineyard, on the other hand, workers used 65% of the time on cutting canes and 35% of the time on pulling canes.

Figure 3. Battery powered pruning tools (left, tying machine; right, pruning shear). These tools are alternatives to conventional hand shears, expected to reduce the fatigue of workers and lower the risk of repetitive motion injuries

Andros Pre-Pruner
We assessed the single-head model of Andros pre-pruner in the spur-pruned ‘Holiday’ vineyard that was used for KLIMA shredder evaluation. Ten continuous rows were pre-pruned and then hand pruned. The adjacent 10 rows were hand-pruned. Andros pre-pruner covered one acre in an hour, leading to a 10% decrease in non-machine labor required for pruning (Table 1). The reduction of labor requirements resulted in a savings of $40 to $80 on a per-acre basis. Given the trellis configuration of the experimental vineyard, the cutting system was placed 20 to 25 inches (51 to 63 cm) above the cordon to avoid the cutting system hitting the horizontal bars of crossarms. In vineyards with larger “V” crossarms, the cutting system can be placed closer to the cordon and thus a larger portion of the wood materials can be pre-pruned. In this case, the cost savings reached $120 to $130 per acre. In addition to cost savings, workers suggested benefit on their end; it was easier to pull canes off when they were pre-cut.

Figure 4. Self-releasing clip installed on a “V” cross arm. These clips allow the shredder to directly pull catching wires from cross arms without human assistance.

Battery-Powered Pruning Tools
We tested battery-powered pruning shears in a spur-pruned ‘Scarlet Royal’ vineyard. Workers who used battery-powered shears can prune two to four more vines per hour as compared to workers using conventional hand shears, leading to a 10% reduction in manual labor input (Table 2). Workers using battery-powered shears felt less fatigue and pruned at a similar pace throughout the day, while workers using conventional hand shears clearly slowed down after 11am.


We also examined battery-powered pruning shears and tying machines in a cane-pruned ‘Autumn King’ vineyard. The use of tying machine allowed workers to tie five to nine more vines per hour than manual tying, improving tying efficiency by 15%. However, battery-powered shears did not improve pruning efficiency, even though workers felt more comfortable making difficult cuts when using those shears (Table 2).
Growers and the manufacturer observed a larger decrease in labor requirements when battery-powered tools were used under similar conditions. We suspect workers who participated in the trial did not fully adapt to the new tools, given that they only practiced for a day prior to the evaluation. We plan to perform more evaluations on those tools in 2023.
Mechanization of pruning can effectively reduce labor requirement and improve efficiency. Depending on the trellis configuration and production scale, growers could save $40 to $200 per acre by adopting mechanical pruning tools. Besides cost savings, pruning mechanization conveys benefits in other aspects. For example, workers could pull off pruned canes more easily after pre-pruning. KLIMA shredder shreds canes in pieces smaller than regular ground shredders, allowing wood materials to break down faster. The quality of cuts and ties improves when battery-powered tools are used.
We truly appreciate the support from table grape growers in Tulare and Kern counties, Pellenc America Inc. and Andros Engineering. This project is funded by the California Table Grape Commission.
Please contact Tian at titian@ucanr.edu for more information.

Resources
Andros pre-pruner: andros-eng.com/ag-equipment/agile-pruning-implements/
KLIMA cane shredder: pellencus.com/products/vineyard/pruner-klima-cane/
Pellenc battery-powered tools: pellencus.com/products/hand-tools/

The Challenge in Management of Aflatoxins in Pistachio and Almond

Aflatoxins are a category of mycotoxins, which are toxic compounds produced by fungi (Myco= µύκης, which means fungus in Greek.) So, aflatoxins are toxins produced by specific types of fungi. These compounds are by-products (secondary metabolites) produced mainly by two fungal species, Aspergillus flavus and Aspergillus parasiticus, which are present in California nut crops and fig orchards when they grow in susceptible substrates. These compounds are very toxic, carcinogenic and cause disease when consumed in large amounts. Because of the high toxicity, aflatoxins are regulated worldwide by governments, dealing with marketing products susceptible to contamination with these mycotoxins. There are several kinds of aflatoxins, such as B1 and B2, produced by the above Aspergillus species. In addition, the latter species produces two more kinds of aflatoxins, G1 and G2. The letters “B” stands for the blue color that these compounds show and the “G” for the green color when contaminated products are placed under a UV light (365 nm wavelength).

Figure 1. (A,B) Early split pistachios serve as the “Achilles Heel” for navel orangeworm infestation and aflatoxin contamination. (C) Suture staining of early split that helps their removal in the sorting belt at the processor.

In the U.S., the tolerance for aflatoxins is 20 ppb (1 part per billion =0.000000001 gr). In the European Union (EU), for all (total) aflatoxin, the tolerance is 10 ppb while for B1 is 8 ppb, and these values are for pistachios and almonds for direct consumption. The tolerances are even stricter for walnuts and dried fruit (4 and 2 ppb for toral and B1 aflatoxins, respectively), and for dried figs, total aflatoxins are 10 ppb while for B1 is 6 ppb.
Because of these strict tolerance thresholds, the U.S. (and to a lesser degree other countries that produce and market products susceptible to aflatoxins) takes extraordinary measures to reduce this contamination as much as possible.

Figure 2. Effect of level of navel orangeworm damage to aflatoxin contamination

Early Aflatoxin Research
For a decade (1991 to 2001), the research in our plant pathology laboratory focused on cultural practices and reduction of damage by the navel orangeworm (NOW) to reduce aflatoxin contamination in almond and pistachio. For instance, in early research on pistachio, we discovered that the early split (ES) nuts (Figure 1) serve as the “Achilles Heel” for infestation by NOW and infection by aflatoxigenic fungi, leading to aflatoxin contamination.
In fact, when samples were collected from several orchards and separated into ES without NOW damage, ES with NOW-damaged nuts and normal nuts (mature nuts but having hulls intact) and analyzed for aflatoxins the results showed that ES contribute a lot in aflatoxin contamination of pistachio as follows: ES (shriveled, i.e., those that had developed early and infested by NOW) had an average of 84% of the total aflatoxins in these samples; if one includes the ES with no NOW infestation, the total levels of the aflatoxins could explain 99.9% of aflatoxins in these samples. Although 20% of the samples represented ES that developed close to harvest had aflatoxins, the levels were only 2 ppb, representing only 0.1% of the total aflatoxins.

Figure 3. Effect of feeding damage by navel orangeworm to aflatoxin accumulation (laboratory experiment with almonds)

These results made us investigate ways to reduce the incidence of ES and also methods to reduce NOW damage. Normal mature nuts had no aflatoxins in these samples. The results were very consistent in two consecutive years. Moreover, when samples were collected and were separated based on their levels of NOW damage, we showed that as the level of damage increased, so did the aflatoxin contamination frequency and amounts (Figure 2). Similarly in almonds, as the feeding sites caused by the NOW larvae increased on almond kernels, so did the aflatoxin levels (Figure 3). Therefore, it is obvious reducing the damage by NOW will result in lower risk for aflatoxin contamination, and this is accomplished by doing sanitation (“mummy shake”) in both almond and pistachio. Avoiding water stress is another approach to reduce susceptibility of trees to aflatoxin contamination. Specifically in pistachio, water stress in early season (May) increases the incidence of ES, and thus increases the risk for aflatoxin contamination.

Figure 4. The two aflatoxigenic mold species that occur in California tree nut orchard.

Biological Control
Because aflatoxin contamination is very sporadic, and because there are no fungicides that would affect aflatoxin contamination, several countries now emphasize a biological control approach by displacing the toxigenic strains of A. flavus and A. parasiticus with the use of atoxigenic strains that are applied directly on to the orchard floor. In California, in cooperation with Dr. Peter Cotty (USDA-ARS), the A. flavus AF36 strain was registered first in 2012 for use in pistachio and then the same product as AF36 Prevail® in 2017 for use in pistachio, almond and figs. As of August 2021, a second product using a different atoxigenic strain, Afla-Guard® GR manufactured by Syngenta Crop Protection, LLC, was registered for use in almond and pistachio. Pistachio and almond growers can use either product starting in the 2022 growing season.
But before moving into the application of either of these products, we need to provide a brief background into the history how this technology had developed over many years of research and the various challenges orchardists have experienced over the years in using the AF36 and/or the AF36 Prevail products.

Figure 5. Very high displacement of toxigenic strains by the applied atoxigenic AF36 strain of Aspergillus flavus in commercial pistachio orchards during 2008 to 2011 when the Experimental Use Permit was

As mentioned earlier, there are two major fungi that can produce aflatoxin and contaminate the susceptible crops, A. flavus and A. parasiticus. The A. flavus produces two strains in the soil based on the size of the sclerotia (resistant, survival structures), the S strain and the L strain (Figure 4). All the isolates of the S strain are toxigenic, while among the isolates of the L strain, there are strains that produce various levels of aflatoxins and others not producing any strains. These latter strains are called atoxigenic.
All the strains of A. parasiticus are aflatoxin producers. An atoxigenic strain called AF36 was found to be among the most frequently encountered atoxigenic strains ranging in incidence from 4% to 12% while other groups of atoxigenic strains ranged from <1% to 2% among the strains in the soil. This strain was determined to be the same that was isolated earlier in Arizona from cotton fields and used there as a biological control agent to reduce aflatoxin contamination in cotton and corn. Therefore, since all the toxicological studies were done by USDA and because the AF36 was the one most frequently encountered in California tree nut and fig orchards, we selected and used it as a biological control agent in the Kearney experimental orchards first to measure displacement of the toxigenic strains.
After 10 years of research in microplots initially and three years as an Experimental Use Permit compound used in 3,000 acres of pistachio, eventually, the AF36 strain was registered for use in pistachio orchards in 2012. The initial carrier of the strain was wheat seed inoculated in big fermenters with the A. flavus AF36 strain. Five years later, the manufacturer was able to register the AF36 Prevail® product, which contains the same AF36 strain and uses sorghum as the carrier, the surface of which is coated with propagules of the atoxigenic strain via a polymer. Recently, a second atoxigenic strain, Afla-Guard GR, was provisionally registered for use in pistachio and almond. There is also an interest now by the walnut and fig industries to have both these products registered for these crops.

Figure 6. Reduction of aflatoxin- contaminated samples after application of AF36 atoxigenic strain during 2008 to 2011.

Challenges
When experiments using the atoxigenic strain AF36 were initiated in 2002, we determined a very high displacement ability of the toxigenic strains in the soil of microplots, which reached almost to 95% displacement at the end of the fourth year, applied once per year. When the EUP was granted in 2008 and 3,000 acres of pistachio were treated with AF36 once per year, the displacement also reached to 95% by the fourth year of application (Figure 5). It was during this time when analyses of first harvest pistachio library samples showed a 40% reduction in aflatoxin-positive samples and an almost 55% reduction in aflatoxin-positive library samples of the second harvest (or reshakes) (Figure 6).

During 2012 to 2019 and after application of the product yearly, we noticed a lower percentage of displacement that ranged from 50% to 70% (Figure 7). The blocks that were treated last in 2011 showed a continuous decrease of displacement from 65% down to about 30%, which remained stable from 2015 to 2017, but there was a jump to almost 50% in 2018 (Figure 7). The untreated fields ranged from about 32% to 20% during this period (2012 to 2018). During the same seven-year period, when library pistachio samples were analyzed for aflatoxins, only in two years (2013 and 2017) were there major reduction level in aflatoxin-positive samples, while in the remaining years, the reductions in positive samples were very small, ranging from 5% to 30%, and in some years (2014 and 2016), there was no reduction at all (Figure 8).
To overcome these challenges and to minimize the influence of treated orchards with AF36 Prevail® by toxigenic propagules (spores) escaping non-treated orchards, we initiated research projects funded by both the pistachio and almond industries on long-term areawide projects. The rationale was that when large area is treated year after year, the influence by non-treated orchards should be minimal. By doing this, we were able to increase the levels of displacement from about 45% in almond and about 65% in pistachio to 80% in almond and 95% in pistachio (Figure 9). This is a significant increase in the levels of displacement of toxigenic strains and we expect now to significantly reduce the levels of aflatoxin-positive samples. A good example for displacement of toxigenic strains is from our research with almonds, where toxigenic strains ranged from 65% to 83% before treatment with AF36 Prevail to about 25% toxigenic Aspergillus in fields treated, while the untreated orchard maintained an incidence of 68% of the toxigenic Aspergillus strains. In the treated orchards, the atoxigenic strains reached a level of about 80% as measured at harvest time. (Figure 10).

 

Moving Forward
The new biological product, Afla-Guard GR is now registered and will be available to pistachio and almond growers to use commercially in 2022. The active ingredient of Afla-Guard GR is the NRRL 21882 Aspergillus flavus strain and the carrier is barley seed. In contrast to AF36 Prevail that is sorghum seeds coated with the spores of AF36 strain of A. flavus, the NRRL 21882 strain is inoculated in the barley seed, i.e., the entire barley seed kernels are “infected” (colonized) by the latter strain.
The Afla-Guard GR product sporulated at higher rates under lower temperatures and lower soil moisture than the sporulation produced by AF36 Prevail when the two strains were compared side by side and under the same conditions. However, since we do not have any results from aflatoxin analyses of pistachio samples, it is still unknown how this product will perform under commercial application. The efficacy of each AF36 Prevail and Afla-Guard GR will be studied in side-by-side commercial fields this year for the first time.
In addition, we are doing studies to overcome other challenges with the commercial application of these products, such as managing predation by ants, rodents and birds, the negative effect of the direct sunlight on the seed inoculum under very high temperatures, the coordination of irrigation either just before or immediately after applying the biocontrol product, etc. All of these are challenges that can differ from orchard to orchard and therefore may affect variably the efficacy of the biocontrol products.
(Co-Authors of this article include: Mark Doster, Plant Pathologist, Pummi Singh, Post-Doctoral Research Associate, Giuseppe Fiore, Graduate Student, University of Bari, Italy, Victor M. Gabri, Staff Research Associate and Graduate Student, Yong Luo, Project Scientist, Ryan Puckett, Greenhouse/Cold Room/Physical Plant Officer and Laboratory Assistant, and Apostolos Papagelis, Agronomist, University of Athens, Greece, John Lake, Laboratory Assistant. All personnel are affiliated presently with UC Davis/Kearney Ag Research and Extension Center, Parlier, Calif. 93648.)
We thank the California Pistachio Research Board and the Almond Board of California (Food Quality and Safety Committee) for funding this research. Also, funding was provided by the USDA/Aflatoxin Elimination Technical Committee and the CDFA/Grant 16-SCBGP-CA-0035. Especially, we acknowledge the extraordinary support of Wonderful Orchards Company, which provided multiple and large-acreage sites for experimentation and hundreds and hundreds of library samples for aflatoxin analyses. It would not have been possible to complete this work and get registration of the atoxigenic strains of Aspergillus flavus without such immense support by this company and its dedicated personnel.

Five Key Items to Look at on Your Vineyard Soil Report

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All throughout the wine grape world and across the U.S., wine grapes are grown on a variety of soil types and climates. AVA regions have started to be defined in places like Arizona where vineyards are thriving on challenging aridisol soils that can be difficult for Vinifera to thrive in comparison to other longer-established regions. Understanding the parts of the soil report and irrigation water quality have become paramount in understanding how to attain the highest level of viable production and maintain the healthiest soils.
It’s not uncommon for the focus of soil reports to center on one item in that report or look at results in a way that can detract from how to get to a fertility program that will serve the budget, crop and soil health most efficiently.
There are five items to look at in order on a soil report to obtain balance and increased overall soil health. It is important when obtaining soil reports to ask the lab you are working with to compute the Cation Exchange Capacity (CEC) and Base Saturation levels. I see a great deal of results from growers who come to my firm looking for recommendations that do not have CEC or base saturation levels defined. It’s impossible to make precise recommendations without these.

Irrigation Water Quality
Dryland-farmed vineyards don’t have this concern or need worry about the problems associated with irrigation water quality. However, if you are using irrigation to water, it’s important to know its quality and understand the pounds-per-acre concepts of potentially problematic minerals being applied. Normally, water is seen as clear and refreshing; not knowing what is contained in water and what normal usage brings is no different than shoveling on bicarbonates, salts, sulfates, boron and chloride directly on the crop. This is an important place where we can find the sources of issues constraining production and limiting soil health and balance.

Cover cropping and getting that green biomass back into the soil is one way to help build a help build soil organic matter levels.

Cation Balance
Cation balance is the most important component of a soil report. Many worry most about pH, but the pH will balance itself out when the specific issues are addressed in the soil. Depending on CEC, one should see Ca levels at 60% to 70%, Mg at 10% to 20%, K at 2% to 5%, Na at 1% to 4% and H at 5% to 10%. It’s important to fall back and understand Mulders Chart, realizing the antagonistic and synergistic relationship between minerals in soils. Identifying imbalances in mineral nutrition can lead to soling mysteries behind cropping outcomes. Cation balance is not overly difficult in most cases, granted it may be a situation where there is a two-to-four-year strategy to attain the corrections needed.

Phosphate Levels
In the southwest, there has been a feeling developed that it is okay to accept lower P levels and production will not be hindered. In other regions, P levels are normally very adequate. These lower levels of 10 to 25 parts per million (ppm) are widely accepted. It has been observed that controlled vigor and balance are attained when soil P levels are found in the 50- to 100-ppm range. Further observations show that as that number approached 100 ppm, there is improved plant health, controlled vigor and improved juice numbers. Delivering P can be challenging, but there are good conventional and organic ways to apply. It most likely serves best to look toward a dry program and have a three-to-five-year goal of building soil P to a level that is acceptable.

Organic Matter
In the desert southwest, I often don’t see organic matter (OM) levels above 1%. Ideally, 4% to 10% is acceptable. In certain regions, this may be a difficult level to attain. Further, in some regions, there can be an issue finding a compost source to help build soil OM levels. Leaning on dry leonardite sources and/or liquid humic additions can be ways to help build soil OM levels. Further, cover cropping and getting that green biomass back into the soil is another means to help build a healthy soil. Increasing OM levels increases CEC, buffers pH and helps nutrient uptake in the soil profile.
Sulfur, Boron, Chlorine and EC
Grapes are not incredibly tolerant of salts and subsequently can be severely hindered by excess amounts. Keeping sulfur, boron and chloride levels to a minimum is very important. Looking at CEC and Ca base saturation levels, one can find the levels acceptable. Keeping boron 1/1000 of Ca or not exceeding 4 ppm is critical to avoid toxicity, with sulfur being 1/3 to 1/2. P is an acceptable range. Cl should be one to two times Na by weight.
Soil health does in fact hinge on mineral balance in the soil. Balancing rations between soil minerals is key to allowing for optimal soil health in vineyards. These are simple ways to break down a soil report and what is maybe influencing it. It is important to spend the time, money and all-around effort to address mineral balance and the items discussed here prior to seeking certain products targeted for soil health.

Aspergillus Vine Canker: An Overlooked Canker Disease of Grapevine in California

Grapevine canker diseases are commonly associated with fungal pathogens of the Botryosphaeriaceae, Diatrypaceae and Diaporthaceae families. These pathogens have been found and described in many cultivars worldwide. Symptoms include internal wood necrosis, stunted or poor shoot development after the budbreak and dieback of cordons or the entire vine. Cankered tissues may also exhibit dark fruiting bodies (pycnidia and perithecia) on the surface, which are responsible for releasing the spores that will lead to further infections in the vineyard.
A different wood canker disease was first detected in the San Joaquin Valley in 1989, affecting excessively vigorous young ‘Red Globe’ grapevines (Michailides et al. 2002). Since then, the disease has been observed on different cultivars, including Chardonnay, Grenache and Crimson Seedless. The pathogen was morphologically identified Aspergillus niger, a member of the group of black aspergilli, or Aspergillus section Nigri, and the disease was named as Aspergillus Vine Canker. From 2003 to 2010, Aspergillus vine canker was detected and monitored in Italy, affecting several table grape cultivars on different growing regions (Vitale et al. 2008, Vitale et al. 2012). In this case, three species of black aspergilli were associated (A. awamori, A. carbonarius and A. tubingensis). Recently, through a collaboration with UCCE farm advisors, we identified Aspergillus vine canker on Grenache and Malbec cultivars in Fresno and Sonoma counties, respectively. Symptomatic vines tested negative for viral infections.

Figure 2. Black sporulation is evident at the surface and underneath the bark of affected tissues, which is key to distinguish Aspergillus from other trunk pathogens that usually form fruiting bodies that are embedded in the wood.

Symptoms
Affected vines are easily distinguishable by their premature senescent leaves during the fall, while healthy vines are still green (Figure 1). A single vine can harbor multiple cankers located on different parts of the vine, including the trunk, cordon and spurs. Black sporulation is evident at the surface and underneath the bark of affected tissues, which is key to distinguish Aspergillus from other trunk pathogens that usually form fruiting bodies that are embedded in the wood (Figure 2). Internally, a brown discoloration is evident in the xylem near the margin of the cankers (Figure 3a), whereas the areas under the sporulation show necrosis and black discoloration near the bark (Figure 3b). In severe cases, the canker can girdle most of the vascular area.

Figure 3a and 3b. Internally, a brown discoloration is evident in the xylem near the margin of the cankers (left), whereas the areas under the sporulation show necrosis and black discoloration near the bark (right).

Current Investigations
Our lab has been focusing on the specific identification of the causal agent of Aspergillus vine canker in California using molecular tools, particularly by constructing phylogenetic trees using DNA sequences of the calmodulin gene. Preliminary data suggest that our isolates correspond to Aspergillus tubingensis, a closely related species to the previously identified A. niger. Since morphological features cannot separate both fungal species, two hypotheses can be indicated, either the old and new isolates correspond to the same species (A. tubingensis) or they are different (A. niger and A. tubingensis). Coincidently, black aspergilli are known to cause sour rot on grape berries. In California, two species (A. niger and A. carbonarius) have been described as causal agents of sour rot disease on table grapes (Rooney-Latham et al. 2008). Therefore, we are currently studying the phylogenetic relationships between Aspergillus isolates from wood cankers and sour rot berries to understand accurately the etiology and epidemiology of both diseases.

Management Strategies
Aspergillus vine canker has not been thoroughly studied given its sporadic occurrence in California. Therefore, the only management strategies include cultural practices, such as obtaining clean plant materials, identifying diseased vines in the fall and removing affected parts by cutting them back below the canker during dormant season or removing the entire vine.

References
Michailides, TJ., W. Peacock, P. Christensen, DP. Morgan, D. Felts. 2002. Plant Dis. 86:75. https://doi.org/10.1094/PDIS.2002.86.1.75A
Rooney-Latham, S., C. N. Janousek, A. Eskalen, W. D. Gubler. 2008. Plant Dis. 92(4):651. https://doi.org/10.1094/PDIS-92-4-0651A
Vitale, A., Castello, I., Polizzi, G. 2008. Plant Dis. 92:1471. https://doi.org/10.1094/PDIS-92-10-1471B
Vitale, A., G. Cirvilleri, A. Panebianco, F. Epifani, G. Perreno, G. Polizzi. 2012. Eur J Plant Pathol 132:483–487 https://doi.org/10.1007/s10658-011-9906-z

Biosolarization: Returning Almond Hulls and Shells to the Orchard to Improve Soil and Almond Tree Health

The California Central Valley supplies 80% of almonds globally, so ensuring the health of these trees is essential. However, young trees are highly susceptible to damage from phytoparasitic nematodes, and chemical fumigation is often necessary to ensure protection. Rory Crowley, a conventional almond and walnut grower, partnered with the Simmons lab at UC Davis to find a natural, sustainable yet effective alternative to chemical fumigation.
“Any thoughtful producer in the Central Valley, whether organic or conventional, understands that we simply cannot continue farming the way we are, especially as it relates to traditional chemical fumigation,” Crowley said. “Indeed, as Dr. Amélie Gaudin has recently said, ‘An entire consortium of scientists has argued for years that our current ways of farming simply cannot go on.’ So, we decided to go with something new.”
Researchers in the Simmons lab, working in collaboration with the UC Davis Western Center for Agricultural Safety, specialize in biosolarization, a soil amendment technology that combines biological, thermal and natural chemical control to reduce plant diseases without fumigation. Biosolarization also provides a closed-loop recycling strategy for agricultural waste streams like almond hulls and shells. These byproducts provide valuable soil amendments due to their high organic carbon content and are co-located with almond orchards.

Figure 1. Biosolarization schematic.

Implementation and Principle
With current technology, three components are necessary for biosolarization:
Soil Amendments: The addition of organic matter (OM) increases the population and activity of beneficial saprophytes (detritus-eaters), which can suppress pathogenic organisms through competition or through the production of biopesticidal chemical compounds. Agricultural and food processing residues act as low-cost soil amendments for biosolarization.
Transparent plastic tarp: Covering moist soil with a clear tarp promotes soil heating through the greenhouse effect. During hot summer months, covered soil can reach surface temperatures over 120 degrees F, temperatures which are lethal to many soilborne pathogens and weed seeds. Elevated temperatures can also leave pathogens more susceptible to biopesticides.
Drip line Irrigation: Irrigation using temporary surface drip lines beneath the plastic tarps fills soil pores, reduces oxygen and hinders gas exchange. When the carbon-rich soil environment becomes anaerobic, fermentative bacteria (Bacilli and Clostridia) can rapidly convert carbohydrates from amendments into toxic organic acids and volatiles.
These three components act synergistically and can provide positive feedback loops. For instance, high microbial activity stimulated by amendments can consume the limited soil oxygen and produce heat as a byproduct. Similarly, the application of amendments and irrigation can change thermal properties of soil and increase solar heating. Because of these combined factors, effective biosolarization treatment durations can be as short as 10 days or less.

Figure 2. Map of field site.

Pre-Plant Orchard Demonstration
Rory’s 8.5-acre almond block in Chico was used as the demonstration site for pre-plant orchard biosolarization in June 2017, and trees were planted the following January. A hull-rich waste stream and a hull and shell mixed waste stream from a local nut processer were selected as soil amendments.
Residues were applied to plots at a rate of 15 tons per acre and tilled to a depth of seven inches. Soil was then covered with transparent tarp and irrigated to field capacity. For comparison, additional plots were treated with solarization (tarped without amendment) or left untreated. Soil remained tarped for six weeks.

Figure 3. Abundance of the phytoparasitic nematode Pratylenchus vulnus.


Nematode Control

Parasitic nematodes (lesion and ring) were detected in soils before biosolarization took place. After 10 days of tarping, nematodes in the first 12 inches of soil were below detection levels in biosolarized soils and nearly undetectable in solarized soils.
When tarps were removed after six weeks of treatment, rows underwent deep tillage in preparation for planting. This effectively reduced nematode levels in the upper 12 inches of soil across all plots regardless of treatment. However, two months after the tillage, reemergence was observed (albeit at low levels) for all but the hull-rich biosolarized plots. As a result, the timing of deep tillage should be considered as a possible complementary control measure. To avoid bringing viable phytoparasitic nematodes from deeper soil layers into the treated root zone, deep tillage should ideally be performed ahead of solarization or biosolarization.

Soil Ecology
Even before tarp application, the incorporation of almond hulls and shells enriched soils with saprophytic taxa (e.g., Bacilli and Streptomyces), demonstrating how amendments can ‘shift’ soil communities to promote organic matter degradation.
After six weeks of tarping, microbes associated with low-oxygen and high-heat environments became significantly enriched in biosolarized and solarized soils (e.g., Clostridia). These microbes can ferment the sugars in almond hulls to produce acetic acid and other biopesticidal chemical compounds.
These enriched taxa remained elevated in treated soils even two months post-treatment. This may indicate prolonged degradation of fibrous organic residues, which has been linked to long-term pathogen suppression due to continued biopesticide production. Some of the microbes identified in biosolarized soils have also been associated with improved soil and plant health outcomes.

Figure 4. Relative abundance of key fermentative anaerobe classes (Bacilli and Clostridia) associated with biopesticidal chemical production.

Orchard Monitoring
Almond tree saplings (Bennett-Hickman, Monterey and Nonpareil varieties with K86 rootstocks) were planted in orchard rows six months post-biosolarization treatment (Jan. 2018), and bi-annual sampling timepoints were used to track soil and crop health through spring 2022. Tree trunk diameters were measured periodically to track growth rate, and soil was periodically sampled to track parasitic nematode re-infestation and soil nutrients levels (Calicum(C), Nitrogen(N), Potassium(K) ).

Almond Tree Growth
During the first year, trees planted in previously-biosolarized rows seemed to grow slower than trees planted in untreated soils. This trend continued until the beginning of the third year, when growth rate appeared to uniquely accelerate in some treated rows. During the fourth year, no differences in growth rate were found between the control and biosolarized trees, indicating successful adaptation of the trees to the treated soil. In one instance, Nonpareil tree diameters were significantly higher in the shell-rich amended rows.
“To be sure, this was a complex project, but the purpose was to prove concept,” Crowley said. “We did that and more. 1After looking at the data, any balanced grower would say that those first two years gave us all a bit of pause. Trunk diameter on the treated row trees were smaller than the controls, yet not once did I think we were going in the wrong direction. I continued to trust Chris and his team, and I trusted the science. I continued to trust my eyes and nose when I smelled the treated soil over against the control dirt. Trunk diameters have now caught up, and in my opinion, will outpace the controls.”
The slowed growth rate of biosolarized trees during the first and second year followed by accelerated growth during the third year suggests that trees may take at least two years to adjust to disturbances caused by degrading residues, but this did not appear to impact long-term growth rates compared to control trees. This also shows the importance of a post-treatment remediation period before crops are planted, though lab studies found soils may recover faster when amendment particle sizes are reduced or applied at lower levels (about 4.5 tons per acre).

Figure 5. Timeline of orchard monitoring.

Nematode Reinfestation
Three years after initial treatment, nematode levels remained low in solarized and biosolarized treated rows, but lesion nematode re-infestation was observed in the untreated rows. Root knot nematodes also became more prevalent in the control soils after three years. Since fumigation has been show to control major phytoparasitic nematodes for approximately two years, solarization and biosolarization appear to at least match the efficacy of conventional pesticides.

Soil Nutrients
Over the first three years of growth, biosolarized soils experienced elevated levels of K, N and C as well as organic matter (OM), a metric associated with improved water-holding capacity, nutrient retention and root biomass. After 3.5 years of tree growth, N, C and OM raw values became elevated in control rows, possibly due to increased nutrient turnover and tree uptake in biosolarized soils.

Figure 6. Colorized NDVI.

Canopy Health
To compare tree health between treatments and tree varieties, multispectral imaging was performed two years after planting and took place each year when the canopy was at peak vegetation. Multispectral imaging captures reflected wavelengths from the orchard to gather data relevant to crop health. For example, healthy vegetation with high chlorophyll levels reflects higher levels of green and near-infrared light than other wavelengths, so rows with more vegetation (and more chlorophyll) would have higher values for green-related metrics than rows with little or poorer vegetation.
Preliminary data have been promising. Certain biosolarized treatments had higher ‘green’ metrics (improved canopy reflectance and color properties) than control trees, indicating greater vegetation levels. However, this benefit was dependent on both soil amendment type and almond tree variety.

Yield and Ripening
Although we do not have yield and ripening data, we do have promising anecdotal evidence from Rory, who managed the orchard last fall during our second harvest. “I got a call from my shaker operator at Nonpareil harvest: ‘Rory, we’ve got a whole row of green nuts.’ I sped over there in my truck. Lo and behold, it was a biosolarization row(s),” he said. “I looked at the control next to it and realized those nuts were ready, dry and shaking off the tree well. When I looked at the biosolarization rows, the nuts were bigger and the quality, by all appearances, was that much better. The nuts were still maturing on the tree, and the overall health of the tree was markedly better. We will prove this out this harvest when we measure crop yield and quality against the controls.”

Conclusions and Recommendations
Both biosolarization and solarization are effective methods for the inactivation of lesion and ring nematodes in the short term, but biosolarization may have longer-term suppression. Effects at deep soil levels (greater than 12”) have not been fully investigated.
Soils treated with biosolarization have higher nitrogen, carbon, potassium and organic matter levels than nonamended soils during the first two years of growth. With fertilizer prices rising steeply, enrichment of plant nutrients in biosolarized soils may be an increasingly important driver for adoption for biosolarization over fumigation or solarization.
Trees may take two years to adjust to disturbances caused by biosolarization.
Growers should conduct trials on test plots before scaling up.
“This powerful alternative to chemical fumigation needs wide adoption, and Chris and his team deserve a huge kudos,” Crowley said. “Onward and upward to the wide adoption and full commercialization of biosolarization with almond hull and shell, and not just in almonds, but in all crops up and down the Central Valley.”
Research to translate biosolarization to almond production has been supported by grants from the National Institute of Occupational Safety and Health (grant #5U54OH007550) and the Almond Board of California (grants #17-SIMMONSC-COC-02 and Q18-BIO-18SimmonsC–0). The authors deeply appreciate the collaboration and support of George Nicolaus to establish the field trial on a Nicolaus Nut Company farm.

References
Hodson, A. K., Milkereit, J., John, G. C., Doll, D. A., & Duncan, R. A. (2019). The effect of fumigation on nematode communities in California almond orchards, Nematology, 21(9), 899-912.
Shea, E., Wang, Z., Allison, B., Simmons, C.W., 2021. Alleviating phytotoxicity of soils biosolarized with almond processing residues. Environmental Technology & Innovation. 23, 101662.
Shea, E, Fernandez-Bayo, J.D., Hondson, A., et al, 2022. The Effects of Preplant Orchard Biosolarization with Almond Residue Amendments on Soil Nematode and Microbial Communities. Applied Soil Ecology. 172, 104343.

Fungal Disease Control Needed for Tomato Production

Powdery mildew is one of the fungal diseases affecting yield and quality in California processing tomato production.

Brenna Aegerter, UCCE farm advisor in San Joaquin County, explained in a UC Ag Experts Talk webinar that tomato powdery mildew (TPM) is caused by three different pathogens depending on environmental conditions. Leveillula taurica is the primary TPM pathogen in arid or semi-arid conditions. Early symptoms of this disease are yellow and light-green lesions on leaves that grow in size. The initial symptoms progress into necrotic and dead leaves with sporulation on either side of the leaf. Spores spread in the air.

Tomato powdery mildew infections increasing one month prior to harvest may affect soluble solids without affecting yield. Early season high disease pressure may significantly reduce yields.

Preventative applications are needed, Aegerter said. Two-week treatment intervals may be too long when disease pressure is high. To optimize chemical control, it is recommended that treatment begin early and to consider other target pests and diseases when choosing a control product. Good coverage that penetrates the canopy is needed. For resistance management, product rotations, tank mixes or formulated mixtures, include sulfur dust in the program when feasible.

Aegerter said younger plants are more susceptible to TPM and late-season fields experience heavier disease pressure. Proximity to other diseased fields and variety tolerance are also considerations. Plant stress may worsen mildew problems.

Field trials in Solano and Fresno growing areas showed that weekly sulfur dust significantly reduced TPM, but the degree varied by location.

Other fungal diseases affecting tomato production are Verticillium wilt, Fusarium, Southern blight and black mold.

Verticillium wilt is an early season disease that is widespread in California production tomato areas. Dry leaves in June and vascular discoloration can be signs of this disease as temperatures warm. Two of the tomato races, 2 and 3, have overcome the Ve resistance. This pathogen is long-lived in soils.

Fusarium crown and root rot infected tomato plants show a slow decline over many weeks late-season. A laboratory diagnosis for this disease is important. No cultivars are resistant.

High temperatures can trigger Southern blight. This fungus needs moisture at the soil line to grow. Aegerter said keeping the tops of the beds dry can help with control.

Black mold fruit rot disease is also a late onset disease. Resistant cultivars and timely harvest can reduce damage. Vine trimming to promote airflow is also advised.

Delayed Spring Growth and Grapevine Production During Drought

After 2021 grapevine budbreak, we received many calls about dead spurs, delayed bud break, stunted shoot growth and poor fruit set. In Fresno County, some severely impacted vineyards suffered a substantial yield loss. In many cases, the problem was delayed spring growth (DSG), and the classic vine symptoms include:

  • Delayed and erratic bud break
  • Stunted shoot growth
  • Excessive berry shatter and poor fruit set

 

The situation was apparently spread across different grape growing regions in California, and UC Davis Department of Viticulture and Enology held a virtual grower meeting to discuss it (the recorded presentation can be found on the UC Davis AggieVideo website.)

Delayed Spring Growth
Grapevine DSG is associated with insufficient rehydration of the vines and may be due to vascular tissue injury, insufficient carbohydrate reserves, excessively dry soil over winter or some combination of these factors. Symptoms can result in significant yield loss and permanent vine damage, resulting in economic hardship for growers. Some vine DSG symptoms are similar to other pest/disease symptoms (e.g., vine trunk disease or soil pests like nematodes/phylloxera.) However, most vineyards we visited had little or no sign of trunk disease or soil pests. Several factors this past fall and winter contributed to widely observed and severe vineyard DSG symptoms:

  • Ongoing drought and increasingly dry soils, especially over winter in vineyards which were not sufficiently irrigated postharvest, or during winter
  • Warmer than normal fall temperatures, including a particularly warm October
  • A sudden freeze in early November

According to CIMIS station data at Five Points, October 2020 was warmer than the last five years’ average and followed a sudden freeze event in November (Figure 1), and warmer-than-normal autumn is a risk factor for DSG. In addition to the November freeze event, October and November 2020 were mostly dry, and a drier autumn could make the freeze worse. Even though the minimal temperature of the 2020 winter might be lower than the last five years’ average according to the CIMIS station data, the DSG’s occurrence and severity varied significantly across vineyards in Fresno County and other parts of California.

Figure 1. Daily minimal temperature from September 2020 to April 2021 at CIMIS Station near Five Points, Calif.

Also, vineyard management, particularly postharvest and winter irrigation, could make a big difference on the results of DSG even if the ambient weather condition was similar. The geographic location as well as vineyard microclimate can sometimes mean quite different consequences in the face of freeze damage. Figure 2 illustrates the variation of daily minimum temperatures from five locations in Fresno County. Typically, vineyards located on the west side had a lower minimal temperature and suffered more freeze damage than vineyards located on the east side. Sand Ranch in particular had the lowest daily minimum temperature among five locations from October to March.

Figure 2. Daily minimal temperature from September 2020 to April 2021 at five UC IPM weather stations in Fresno County.

To make matters worse, Fresno County saw much less precipitation during the months of November and December 2020 than the last 20 years’ average (Figure 3). These drier months might offer the perfect conditions for DSG. Although precipitation amount was normal in January 2021, February was yet another dry month in comparison to historical averages. Lack of soil moisture before bud break is another major risk factor for DSG.

Figure 3. Monthly precipitation from October 2020 to March 2021 in Fresno County.

Grapevine winter freeze damage and DSG have similar symptoms and can be difficult to differentiate. Winter cold damage or freeze injury damages vascular tissues and can thus interfere with water, carbohydrate and mineral translocation, causing symptoms similar to DSG. A lack of soil moisture can impair vine rehydration, making vines suffer water stress and causing DSG symptoms directly. Additionally, vines might be more vulnerable to cold injury even though the minimal temperature in the past winter, such as 25 degrees F at Sand Ranch, might not cause significant freeze damage on most Vinifera grapes.

Maintain Vine Health
Vineyard conditions should be considered to avoid DSG and possible cold damage:

  • Abiotic or biotic stressed vines (e.g., severe water stress and overcrop, nutrient deficiency, pest/disease)
  • Young vines
  • Late ripening and cold tender varieties
  • Certain rootstocks, including Freedom and Harmony
  • Insufficient soil moisture during the dormant period (e.g., October to March in the San Joaquin Valley)

Generally, maintain vine health over the growing season and assess soil moisture as the vines enter dormancy, watering if needed. Too many clusters with not enough leaf area can weaken the vines and deplete the trunk and root’s carbon reserves, which are needed to maintain respiration over winter, help prevent freezing and nourish the vines as they regrow in the spring. To maintain a functional vine canopy, irrigate as necessary to support photosynthesis without stimulating excessive growth. If pests or diseases are present in the vineyard, such as powdery mildew, nematodes, grapevine trunk disease, virus, mites and leaf hopper, a good assessment of canopy health is important. Grapevines with severe defoliation or small canopies will be of great concern, and management should focus on better addressing pest and disease problems to avoid early defoliation.

A young vine has its inherent nature of vulnerability due to a lack of sufficient carbon reserves. Therefore, severe water stress and overcropping should be avoided, and irrigating the soil before a freeze event (e.g., late October and early November) can be greatly beneficial to provide heat protection for young vines.

This past spring, we noticed some susceptible varieties might suffer greater damage from DSG, and that has been consistent with the reports from other growers. Chardonnay and Pinot gris have been reported frequently on DSG, although both varieties are also susceptible to winter freeze.

Rootstock can also play an important role in DSG. Certain rootstocks (e.g., 5BB and Freedom) are more susceptible to DSG than others (e.g., 1103 P), according to results of UCCE rootstock field trials in different growing regions of California. Thus, growers who have the susceptible rootstock might want to take extra care of the vines, such as irrigating the soil during the dry winter, so that the risk of potential DSG might be minimized.

Manage Soil Moisture
Last but not least, lack of soil moisture might be the most important yet manageable factor contributing to most DSG farm calls. As discussed previously, drier October, November, December and January months posed a great risk of DSG as well as inhibited rehydration of the vines, which can also lead to a greater risk of freeze damage. However, water availability during the drought years might be significantly reduced or expensive.

Therefore, irrigation during the drought years can become the dilemma. Growers need to balance the cost and reward of irrigation vs. no irrigation during drought years. Greater than 20% yield loss has been reported for some vineyards in Fresno County in 2021, and DSG might play a large role in it, although the record summer heat and seasonal variation could also result in loss. Finally, the consequence of DSG on Fresno vineyards varied greatly. Some vineyards appeared to be significantly stunted after budbreak and later fully recovered due to irrigation. Some vineyards might suffer multi-year yield loss due to the weakened canopy and few desired canes to prune.

In the face of upcoming potential drought, growers can use multiple tools to reduce or eliminate the effect of soil moisture deficit. Many tools (e.g., shovels, soil augers, moisture sensors) can provide great benefits for assessing soil moisture and help growers determine whether or not to irrigate. Weather stations can also provide great amounts of information regarding the minimal ambient temperature as well as the amount of local precipitation, since temperature and precipitation can vary greatly from one vineyard to another. UC IPM has seven weather stations in Fresno County and one station in Madera County in cooperators’ vineyards, and those stations can offer both temperature and precipitation amount, serving the growers whose properties are nearby the station.

A New Biocontrol Approach for the Reduction of Pierce’s Disease in Vineyards

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Though vineyard managers continually face many challenges to optimal productivity, Pierce’s Disease (PD) represents a particularly formidable threat due to limited options for effective prevention and control. PD is a degenerative, deadly and costly disease of grapevines caused by Xylella fastidiosa subsp. fastidiosa (Xff) bacteria, Gram-negative rod-shaped microbes with characteristic large pili. Though hosted by many plant species, these bacteria are easily spread to grapevines by insect vectors such as blue-green and glassy-winged sharpshooters (Figure 1, see page 41). Xff colonize the gut of sharpshooters and are transmitted to grapevines as the insects feed on vines.

Pierce’s Disease: A Major Threat
Once inside a grapevine, Xff bacteria impede the normal function of xylem tissue (transport of water and nutrients ‘up’ from roots to stems and leaves.) This damage induces the characteristic chlorosis and scorching of leaves, causing early symptoms of PD which mimic water stress. However, the insidious and cumulative damage caused by PD eventually kills entire vines in one to five years.

Figure 3. Viral bacteriophage particles of XylPhi-PD precisely targeting their bacterial host (photo courtesy Inphatec.)

PD represents a major threat to U.S. wine regions, accounting for widespread economic damage (e.g., roguing and replanting of vines, low fruit production, etc.) and costly deployment of resources aimed at disease moderation. PD has been reported in 28 California counties, covering most of all wine-producing regions. State Extension teams in Texas, Arizona and North Carolina have reported significant outbreaks in 2021. Lost production and vine replacement has been estimated to cost grape producers about $56.1 million annually as of 2014. Further, a 2016 survey of nearly 200 growers and managers in Napa and Sonoma counties revealed that 73% of respondents identified PD was one of their top three management problems.

Figure 1. Blue-green sharpshooter (top) and glassy-winged sharpshooter (bottom), two of the main insect vectors for spread of Xff (photos courtesy Inphatec.)

Few methods for controlling and treating PD have been made available, with efforts historically focused on controlling the sharpshooter vector (e.g., insecticides, trapping, monitoring, inspections) or roguing seriously ill vines (rogue, replant), all of which has achieved only limited success. However, a new option that reduces PD in grapevines is now available.

New Bacteriophage Injection for PD
XylPhi-PD is a novel, OMRI-listed, biological treatment for PD, a cost-effective break-through technology developed exclusively for viticulture by A&P Inphatec (Figure 2, see page 32). XylPhi-PD contains a cocktail of viral bacteriophages (Figure 3, see page 32) that are injected into a grapevine (‘bacteriophage’ are bacteria-killing viruses that selectively infect bacteria but do not infect the eukaryotic cells of plants or animals.) These virus particles enter and destroy Xff bacteria, thus limiting bacterial growth and the xylem-clogging damage to the plant. Hundreds of phage particles can be manufactured inside an Xff bacterial cell after infection by a single phage particle. The Xff bacterial cell eventually dies and releases all newly created phage particles to seek and destroy more Xff bacterial cells (Figure 4).

XylPhi-PD applications are made by injection of the product into the vascular system of grapevines. Applications are made directly into the active xylem tissue of the plant using a pressurized injection device, the Xyleject Injection System (Figure 5).

XylPhi-PD can be flexibly applied as a treatment when disease symptoms appear, as a preventative to protect growing vines, or whenever conditions may lead to disease. As with most any disease situation, disease prevention or treatment early in the disease process provides much better outcomes than treatment of later-stage severe infections. XylPhi-PD is available in 100-mL vials (treats up to 300 mature vines or 600 young vines.) The product has no restricted-entry interval (REI), requires minimal personal protective equipment (PPE) when used in accordance with label directions and is approved for use in organic production (OMRI-listed, Organic Materials Review Institute).

Efficacy Overview
Multiple studies have been conducted to support the development and commercialization of XylPhi-PD, and results have provided much insight regarding the product’s efficacy profile and use strategies. Brief overviews of some of these studies follow:

Greenhouse pilot study (Texas A&M, 2014):
Design: 30 greenhouse grapevines inoculated with Xff. 15 vines treated with XylPhi-PD once at three weeks post-inoculation, 15 vines received only buffer. Visual symptoms of PD assessed 12 weeks post-inoculation.

Results: XylPhi-PD reduced PD incidence by 87%.

Natural infection field trial (Texas A&M, 2015):
Design: 30 Chardonnay and 30 Cabernet Sauvignon vines in an area with high natural PD pressure randomly assigned to each of the four groups. Vines treated zero, one, two or three times with XylPhi-PD during the summer.

Results: Disease incidence in the XylPhi-PD-3X group was significantly reduced by 44% (P = 0.047) compared to controls (10% vs 18%). Activity of vectors positive for Xff was high during the trial period.

Figure 4. Death and rupture of a bacterial cell, releasing newly created phage particles to seek and destroy more bacterial cells (photo courtesy Inphatec.)

Challenge studies, prevention and therapeutic treatment (California University, 2017):
Design: Prevention study – 15 Chardonnay and 15 Cabernet Sauvignon vines treated with XylPhi-PD and then challenged twice with Xff.

Therapeutic study – 30 Chardonnay and 30 Cabernet Sauvignon vines/group challenged twice with Xff and then treated zero, one, two or three times with XylPhi-PD.
Results: Prevention – prechallenge XylPhi-PD significantly reduced incidence of PD symptoms by 75% in Cabernet Sauvignon vines (P < 0.10) and 100% in Chardonnay vines (P < 0.05) vs controls.

Figure 5. Injection of XylPhi-PD into trunk of mature grapevine. Xyleject Injection System (Pulse Biotech, LLC; Lenexa, KS)

Therapeutic – three post-challenge XylPhi-PD treatments significantly reduced incidence of PD symptoms by 90% in Cabernet Sauvignon vines (P < 0.05) and 77% in Chardonnay vines (P < 0.10) vs controls.

Multi-year natural infection field trial (2017-20; Sonoma, Calif.):
Design: Two groups of healthy Zinfandel vines were tracked in a high PD-pressure, organic vineyard for three seasons (Ridge, Lytton Springs). One group (n=71) received XylPhi-PD three times/summer, while controls (n=94) only received buffer.
Results: After three years of treatment, vines treated with XylPhi-PD show much less PD incidence than control vines as assessed by both qPCR (-60%) and visual PD symptoms (-72%). Vines treated with XylPhi-PD also generated higher fruit yields, averaging +1.34 lb/vine (+21%) more than control vines.
4-site, 3-year, Natural Infection Field Trial (2019-21; Sonoma, Calif.):
Design: A three-year, multi-location commercial (Wilbur-Ellis) field study evaluated the efficacy of XylPhi-PD against endemic PD across four sites and three production seasons. The extensive research effort began in 2019 when a study was conducted that involved 400 vines (300 Chardonnay, 100 Pinot Noir) at three Sonoma County commercial wineries with a history of PD (one winery had two test fields) (Figure 6). All four commercial vineyards were historically high PD sites, and despite continual roguing and insecticide use in the past, a persistent reservoir of Xff remained in the vineyards from previous infection cycles. Thus, each site included vines with both early-stage and chronic/severe PD.

Figure 6. Locations of four sites used for three-year field study.

Vines were randomly selected in treatment blocks at each site and assigned to either of two treatment groups as follows:

-Control (untreated): n=200 (50/site);
-XylPhi-PD: three treatments (Jun/Jul/Aug); 80 µL of XylPhi-PD injected twice in the trunk and once in each cordon (4 to 6 injections = one treatment); n=200 (50/site).
Six petioles from each vine were collected in September for analysis by quantitative polymerase chain reaction (qPCR) and confirmation of Xff infection. All study vines were also visually assessed by trained observers for PD development. Insect traps were placed at each study site in an attempt to monitor vector pressure.

A continuation of the same study protocol was followed in 2020 and 2021, allowing two additional seasons of treatments and observations for the same vines/blocks at the same sites/wineries. In addition, treatments and observations of additional vines were initiated in 2020 at each site (n=50/site, 200 total), repeated again in 2021 (Figure 7). As a result, three groups emerged from the study for tracking and evaluation:

Figure 7. Study design and timeline for three-year multi-site field study.

Vines with three years of treatment (three-year treated, n=200)
Vines with two years of treatment (two-year treated, n=200)
Non-treated controls (n=200)

Results
Comparative outcomes for vines qPCR-positive for Xff are summarized in Figure 8, see page 36. Under the conditions of only mild to moderate PD pressure and low vector populations, sequential year-to-year use of XylPhi-PD generated impressive results. Incidence of Xff positivity fell 24% and 45%, respectively, for vines receiving two or three years of treatment compared to untreated controls. Improvement in the three-year group was significant (P < 0.05) vs controls. The few vines remaining Xff-positive in the two- and three-year groups were chronic infections that would be rogued.

Figure 8. Vines qPCR-positive for Xff, or vines showing visual signs of PD. Summary of four sites in Sonoma County.

The visual assessment of vines for signs of PD was another important study parameter, and outcomes (Figure 8) were similar to those using qPCR confirmation of infection. Vines treated with XylPhi-PD for two years generated a 27% reduction in visual PD incidence compared to controls, while vines treated for three years showed double the benefit, a significant 54% reduction (P < 0.05) of PD incidence. The similarity of these data with qPCR results suggests that visual assessments can help vineyard managers tangibly gauge the efficacy of XylPhi-PD.

Figure 9. Average fruit yield for Chardonnay vines at one site (D).

Notably, XylPhi-PD continued to protect against PD infections at all four trial sites for the three years of observations, with no new infections detected in the three-year treated group. In contrast, the control group had ~2% to 4% new infections.
Fruit yield was measured at one study site (D) at the study’s conclusion in 2021 (Figure 9, Chardonnay, eight- to ten-year-old vines). Compared to untreated controls, vines in the group treated with XylPhi-PD for three years averaged 5.1 lb (+17%) more fruit per vine than controls. Vines treated for two years were intermediate (3.1 lb, +10% more fruit vs controls).

Usage Recommendations
XylPhi-PD can be applied as a preventive treatment to protect growing vines, as a therapeutic treatment when disease symptoms become visible, or anytime production conditions may lead to disease pressure.

Table 1. XylPhi-PD dosage options and number of applications per vial (100 mL).

Locations selected for application of XylPhi-PD can be based on the age of the plant, the pruning style and/or the training system utilized for the plant. The product is to be injected into the active xylem vascular tissue above ground level. Two examples of injection strategies appear in Figure 10, see page 37. On established vines, for example, one or two injections can be applied in the trunk with an additional injection in each cordon or spur. For young, recently planted or radically pruned vines, apply two or three injections into shoot, two to six inches above the ground. For all scenarios, the total number of injections administered to a vine define one ‘application’ of XylPhi-PD.

Figure 10. Recommended XylPhi-PD injection locations.

For most production situations (medium to high PD pressure), two or three applications of XylPhi-PD are recommended during each growing season at near-monthly intervals (Figure 11, see page 37). This frequency of application has been demonstrated to provide optimal PD control under various levels of PD pressure. The volume of XylPhi-PD administered can also vary depending on the age of plants being treated and PD pressure.

Figure 11. Examples of XylPhi-PD application programs involving medium to high PD pressure.

The quantity of XylPhi-PD used in XylPhi-PD treatment programs can vary based on the number of injections/vine, the concentration of product/injection and the number of applications/year. Growers and PCAs have options and flexibility to match doses and the number of applications to their specific conditions and risks. Table 1 summarizes some of these options and their impact on the amount of XylPhi-PD used and number of vines treated per 100-mL vial.

Treatment Strategies for PD Management
Several recommendations for managing PD across an entire vineyard have emerged from field use experience with XylPhi-PD. These recommendations largely depend on the scope and distribution of PD in a particular vineyard or block.

Figure 12. Strategies and options for treating areas within vineyards or blocks.

As usual, vines demonstrating severe and/or chronic PD infection should be rogued per IPM protocols.

Vines appropriate for XylPhi-PD treatment should be identified.

Figure 13. Examples of visual damages caused by PD (photos courtesy Inphatec.)

These appropriate vines should be treated with recommended doses of XylPhi-PD at two or three seasonal applications as needed for mature vines or replants (per label directions).
It is the second step, identifying which vines to treat, that can sometimes pose a quandary for production managers. To help in this process, three strategic options can offer direction for developing a customized plan for vineyard-wide PD management. Based on evaluations regarding the spread of infection and site specifics for a particular vineyard or block, a treatment strategy can be selected from the following (Figure 12):
Targeted buffer zone: Treat all vines in any defined area with high PD activity (>2% symptomatic vines) and/or vector activity, such as near a riparian area.
Precision spot: In large areas with few symptomatic vines, mark/identify affected vines and treat only them and their immediate surrounding neighbors.
Entire block: In large areas with multiple scattered symptomatic vines, in the presence of vectors, full-block treatment is needed to reduce overall PD pressure.
In addition to these three options, the duration of treatment (multiple years) is also a critical consideration. As discussed earlier, field studies have demonstrated the cumulative value of consistent treatment with XylPhi-PD over multiple years for reducing the level of PD in a vineyard or block, even when under low PD pressure. As always, prevention of severe, chronic disease is the best approach, and consistent long-duration use of XylPhi-PD appears to substantially diminish PD progression and pressure in vineyards.

Identifying PD
Some of the visual signs of PD damage are presented in Figure 13, including characteristic chlorosis (leaf scorching), irregular lignification and berry shriveling, and ‘matchstick’ petioles. In general, PD is likely present in a vineyard if the following four symptoms are observed late in the season:
Leaves scald in concentric rings or in sections
Leaf blades abscise, leaving petioles attached to the cane
Bark matures irregularly
Fruit clusters shrivel or raisin
However, damage caused by various other diseases, water stress, pests or nutrient deficiencies/imbalances may produce symptoms similar to those caused by PD. Therefore, PD must be laboratory confirmed by detection of Xff by qPCR testing on late-season/fall petioles (e.g., UC Davis Foundation Plant Services, Texas Plant Disease Diagnostic Lab, Arizona Plant Diagnostic Network).

Conclusions
PD is an extremely challenging problem for wine producers and their consultants. A biological control approach with XylPhi-PD offers a fresh opportunity to help manage PD and limit losses associated with the disease. In multiple studies, XylPhi-PD treatment of diverse wine varietals prompted reductions in PD incidence and/or severity under conditions of both natural and challenge infection with Xff. These favorable outcomes distinguish XylPhi-PD as a targeted and cost-effective strategy for effectively protecting valuable vineyards against PD.

Always read and follow product label directions. Not registered in all states. EPA Reg. No. 93909-1. Operators of injector must undergo training and be certified by Pulse and must follow instructions in device manual. XylPhi-PD is a trademark of A&P Inphatec. Xyleject is a trademark of Pulse Biotech.

To view a field trial demonstration click here https://www.youtube.com/watch?v=LzwQv-hfcew

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