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Mechanization Improves Pruning Efficiency in Table Grape Vineyards

By
Tian Tian
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Figure 1. Andros pre-pruner in a spur-pruned vineyard. The machine snaps canes and removes part of the wood materials before workers cut canes to spurs (all photos courtesy T. Tian.)

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

By
Themis J. Michailides and Ramon Jaime
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Themis Michailides and Plant Pathologist Mark Doster examine AF36 seeds spread in the field. The atoxigenic AF36 strain was registered for use in pistachio orchards in 2012.

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

By
Vern Johnson
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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 (photos courtesy Cameron Newell and Jesse Kay-Cruz, Xerces Society.)

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

By
George Zhuang, Akif Eskalen, Molly Arreguin, Karina Elfar and Marcelo Bustamante
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Figure 1. Affected vines are easily distinguishable by their premature senescent leaves during the fall, while healthy vines are still green (all photos courtesy A. Eskalen.)

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

Leafhoppers Pose Challenges in Vineyards

By
Cecilia Parsons
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Western grape leafhopper, variegated leafhopper and Virginia Creeper leafhopper all suck out liquid from grape leaf cells, causing loss of photosynthesis, reduced vigor and even leaf drop when in high densities. Affected leaves will have white stippling (photo by Jack Kelly Clark, courtesy UC Statewide IPM Program.)

Erythroneura leafhoppers can be a significant insect pest in organic vineyards as well as regions of California where biological control is inadequate.

The Western grape leafhopper (Erythroneura elegantula) is a pest in the San Joaquin, Sacramento, Central Coast and North Coast regions. The variegated leafhopper (Erythroneura variabilis) is in southern California, San Joaquin Valley, southern Sacramento Valley and occasionally found in Napa County. Virginia Creeper leafhopper (Erythroneura ziczac) is mostly found in the Sacramento Valley and Sierra Foothills, but over the past 10 years has started to infest North Coast vineyards as well, especially Lake and Mendocino counties.

The Western grape leafhopper, variegated leafhopper and Virginia Creeper leafhopper all suck out liquid from grape leaf cells, causing loss of photosynthesis, reduced vigor and even leaf drop when in high densities. Affected leaves will have white stippling. If high populations of leafhoppers are present, fruit quality and yield can be affected. Adult leafhoppers can also be a nuisance to workers at harvest.

Leafhoppers overwinter as adults in leaf litter and weedy vegetation in and around vineyards. They emerge in the spring to feed on new shoots and lay eggs under the surface of the leaves. Adults and nymphs feed on the leaves.

Houston Wilson, Cooperative Extension Specialist (Dept. of Entomology, UC Riverside) at the Kearney Agricultural Research and Extension Center, said the Western grape leafhopper is usually controlled by the egg parasitoids Anagrus erythroneurae and Anagrus daanei, which are common in many California vineyards. Parasitoids attack the egg stage, and if their population builds in a vineyard, they can keep leafhoppers in check. These parasitoids overwinter outside of the vineyard, primarily on coyotebrush and blackberry, and it has been shown that the closer these plants are to the vineyard, the earlier parasitoid activity will begin in the vineyard.

Biological control of the variegated leafhopper and Virginia Creeper leafhopper is more challenging since the populations of parasitoids that attack these species tend to vary from region to region. Additionally, eggs of the variegated leafhopper are deposited deeper into the leaf tissue, which makes it more difficult for parasitoids to access and attack. Wilson said the key parasitoids for these species include Anagrus daanei and Anagrus tretiakovae. While Anagrus daanei can be found in the Central Valley, Sierra Foothills and Coastal regions, Anagrus tretiakovae is much more limited.

Wilson received funding from DPR in 2015 to research the different strains of leafhopper parasitoids in California and determine why Virginia Creeper leafhopper eggs in the North Coast wine grape regions were not being parasitized. Surprisingly, Anagrus daanei in the North Coast appear to not attack Virginia creeper leafhopper, even though they will readily do so in other regions of the state. Between 2015-17, Wilson worked to introduce a strain of Anagrus daanei into the North Coast that would attack Virginia Creeper leafhopper, but it did not establish. Wilson is hoping to reinitiate this area of his research program in the next year.

Many grape growers rely on the use of systemic neonicotinoids for control of leafhoppers since these products can be quite effective. As such, recent leafhopper outbreaks have been primarily limited to organic vineyards. That said, there is potential for both resistance and/or regulation of neonicotinoid use in California, at which point effective biological control will be critical to all growers.

CRB Plans New ACP Strategies

By
Cecilia Parsons
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Adult Asian citrus psyllid feeding on new flush. Citrus industry efforts are aimed at controlling this pest which can transmit citrus greening disease, or Huanglongbing (photos courtesy Citrus Research Board.)


Citrus growers throughout California can apply to be part of the Citrus Research Board’s (CRB) California focused Citrus Research and Field Trials (CA-CRaFT) program. This project is aimed at development and demonstration of additional mitigation measures for Asian citrus psyllid (ACP) control across all citrus growing regions of California.

Project Manager Ariana Gehrig said the project will have an advisory committee to review and select grower applications to implement innovative psyllid management strategies for enhanced grove-level control of ACP. Growers who apply for this project will receive reimbursement for costs associated with their participation.

In the first year of the project, growers will be invited to apply and implement additional control methods in commercial groves. Data collected will be used to demonstrate changes in psyllid populations resulting from mitigation measures. Data collection and implementation of control strategies are expected to continue into the second year. Findings will be shared with citrus growers to promote effective treatments and share best practices.

Gehrig said there will be two types of ACP mitigation efforts: preventative and threshold. Preventative measures could involve use of living wind breaks or fence-type barriers to protect citrus orchards from ACP infestations. Use of trap crops grown in or adjacent to orchards is another type of mitigation measure. The threshold category might include border treatments, ACP repellents or ant control. Biological control agents include the release of the ACP parasitoid Tamarixia radiata or generalist predators.

Gehrig said although participation is open to all citrus growers, the advisory committee will make selections based on growing region, variety of citrus, age of groves and mitigations selected. Growers may apply for projects in multiple blocks. The preferred size is 5 to 40 acres.

Grower applications will be available soon for the CA-CRaFT project. The CRB was awarded $3,438,059 from the Huanglongbing Multi Agency Coordination Group to support the CA-CRaFT project. CRB will administer the program for two years with intent to renew.

“We are excited to develop the first CRaFT project for citrus in California as this project will bring new energy to the fight against HLB and benefit growers across the state while investing in vital research,” said CRB President Marcy Martin.

Technological Advances Coming for Strawberry Production

By
Cecilia Parsons
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The California Strawberry Commission’s technology production team created a retrofittable cutting apparatus for mulch hole punching. The larger hole made by the new tool allows more water and sunlight to reach the strawberry plants (photo courtesy CSC.)

While strawberries are one of California’s high-dollar crops, the labor required to not only harvest, but to perform other cultural tasks comes at a considerable cost. UC figures show that labor costs can be $25,000 to $39,000 per acre. In addition to hand harvest, there is runner cutting, pest monitoring and treatment, and the simple but laborious job of cutting holes in the plastic mulch at planting.

Automation has not yet come for harvest, but technological advances in other areas are promising. Dr. Mojtaba Ahmadi, senior production automation engineer with California Strawberry Commission, said that since 2020, the CSC has started to stimulate third-party companies for development of automated runner cutters and to investigate some of the technical aspects of this. Runner cutting is the second largest labor cost after harvest, Ahmadi said.

The engineering team has developed a deep learning framework to detect and identify runners by using RGB image data as well as exploring different methods to improve data collection. Ahmadi said the CSC has also collaborated with the Massachusetts-based Strio AI, a robotics startup, to develop an automated runner cutter.

This effort was successful in building a robotic platform that was able to maneuver in strawberry fields and, with use of a robotic arm, fusion RGB and depth data, successfully performed runner cutting.

Obstacles to the use of robotic runner cutting, such as cost, complexity of the electronics and maintenance difficulties ,have yet to be overcome, Ahmadi said.

Lygus monitoring and treatment is another focus of CSC technology efforts. Ahmadi said work is continuing on machine vision technologies in combination with vacuum technology. The aim is to determine how effective the vacuuming operation is in removal of lygus.

“We know speed matters, both tractor speed and vacuum air speed as well as height of the vacuum from canopy level,” Ahmadi said. Monitoring these can help the tractor driver know if the settings are accomplishing the job.

Plastic mulch hole cutters are typically driven through fields just prior to planting. Ahmadi said that the hole punchers leave narrow openings in the plastic that may prevent adequate water and sunlight from reaching plants. The production team developed a tool that can be attached to the current hole punchers to widen the holes without deforming the planting hole in the soil. Grower testing has proved this modification can be applied in commercial strawberry production.

Don’t Let Alfalfa ‘Limp Along’ in Drought

By
Cecilia Parsons
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Tulelake alfalfa growing on residual moisture in late June 2021. Soils there have high water holding capacity to sustain crops during the early part of the growing season. Alfalfa’s deep rooting systems can tap into soil moisture (photo by D. Putnam.)

It is a mistake to let an alfalfa field ‘limp along’ on inadequate irrigation throughout the growing season, letting yields and quality suffer. The better strategy for hay production, according to UCCE Specialist Dan Putnam, is to fill the soil profile early and get as much yield as possible and then allow the stand to go dormant.

“It is a resilient crop. It can come back within the fall when it receives some moisture,” Putnam said.

Filling the soil profile early will give growers the two to three cuttings that are usually higher in yields and quality than those later in the season.

Alfalfa growers throughout the state can develop strategies to keep good alfalfa stands productive in drought conditions. Putnam said the first step is to decide which fields or parts of fields will benefit the most from what irrigation water is available. Those should have priority. Alfalfa stands nearing the end of their productive life, those on soils that do not hold moisture well or spotty stands are best left to go dormant to direct water to alfalfa stands that will benefit the most.

Ending irrigation in mid- to late summer for alfalfa fields will not end their productive life. The stands will turn brown and go dormant, but generally won’t be lost. Depending on the soil type, Putnam said, most of the time alfalfa will recover with fall rains or irrigation. Putnam pointed out that 60% to 65% of annual alfalfa yields in most parts of California are achieved by mid-July.

Putnam wrote in a UC publication that alfalfa has a key role in California’s water-uncertain future due to its high flexibility during times of insufficient and excess water. Alfalfa’s deep roots tap into residual soil moisture. Multiple harvests can give partial economic yields when irrigation ceases. Alfalfa roots survive summer dry-downs and will come back when re-watered. Alfalfa fields can be flooded in winter to recharge aquifers. The crop also has high salinity tolerance.

Alfalfa has proved to be highly flexible and resilient in surviving droughts while sustaining productivity, even when as little as half the water requirement is applied, Putnam said. The resilience of alfalfa was demonstrated during the 2021 drought in the Tulelake area where a full yield of two cuttings of alfalfa was observed with zero irrigations. Only six inches of rainfall occurred before March. Alfalfa roots were deeper than eight feet. The soils there have excellent water holding capacity, Putnam said, but the production showed the resiliency of alfalfa with limited water supply.

Further discussion of strategies for drought conditions can be seen at a blog on drought at https://ucanr.edu/blogs/Alfalfa/.

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

By
Amanda Hodson, Rory Crowley, James J. Stapleton, Tate Lone, Christopher Simmons and Emily Shea | UC Davis
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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.

Tree Protectors are Simple but Important Tools for Young Trees

By
Cecilia Parsons
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Paper cartons that come with the bare root or potted trees from the nursery are the most frequently used tree protectors (photo by C. Parsons.)

Protecting newly planted almond trees from herbicide damage, sunburn or vertebrate pests can help ensure a healthy, productive tree at maturity. There are products that nurseries provide to protect new trees and others that growers choose to purchase for specific uses. Which product to use and how long it should be left in place are important considerations.

Paper cartons that come with the bare root or potted trees from the nursery are the most frequently used tree protectors. Coated with a waxy type material or plastic film, the paper cartons primarily serve as a barrier to herbicides sprayed down tree rows.

Luke Milliron, UCCE orchard advisor in Butte, Glenn and Tehama counties, said there is concern that the paper cartons could disintegrate before the new trees are hardened off and resistant to herbicide injury. On the other hand, leaving paper cartons on the tree too long can also pose risks. In UCCE’s Sacramento Valley Orchard Source, Milliron noted that the paper part of the carton can disintegrate over time, but the coating can hold moisture on the tree trunk. Long-term moisture on the trunk can present the possibility of a Phytophthora infection. Milliron stressed that any trunk protector that keeps the tree trunk wet for a prolonged period is a risk for disease. Even if the carton does not disintegrate, leaf litter can accumulate inside the carton and hold moisture against the trunk or crown of the tree.

Milliron noted that white paint on the tree trunk alone does not protect young almond trunks from herbicide damage. The carton provides the protection from herbicide damage.

The recommendation from former UCCE Advisor David Doll, The Almond Doctor, is to keep cartons on through the summer of the second year for protection for the late spring burn down. That leaves an opportunity to remove them before debris and tree growth makes it difficult.

Cliff Beumel with Agromillora Nursery said other products that provide protection are also available. Taller versions of the carton protectors at 18 inches use the wax type coating but are not as wide as the conventional cartons. Grow tubes, a plastic product, are used with smaller trees. These can provide longer protection from herbicide or other injury and are less likely to trap moisture against the trunk. They come at a higher cost but can be re-used.

Another variation is plastic protection that is white on the outside and black on the inside. Beumel said their cost may be lower, but labor is required to place them on the trees. They do not stay consistently wet and pose less problems for disease infections. One of their main benefits is these protectors block the sun and prevent suckering.

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