@dmin_westcoastnut, Author at West Coast Nut


Bolster Your Defenses Against Ag Crime

Wondering where to find your stolen tractor, all-terrain vehicle (ATV) or other farm equipment? Try searching Craigslist, OfferUp or Facebook Marketplace.

Rural crime experts say thieves often use those social media sites to sell stolen property.

“Some thieves post photos of stolen farm equipment on those sites, conduct the sale online and then send the buyer to the field to take possession of it,” said Don Stuhmer, president of the California Rural Crime Prevention Task Force (CRCPTF) and a detective with the San Joaquin County Sheriff’s Office. “The buyer never sees the seller and doesn’t even know it’s stolen property.”

Online marketplaces have become one more way thieves are selling what they’re stealing from farmers across California’s Central Valley. Tulare County’s Rural Ag Crime unit alone saw $2.5 million in ag theft last year, said Sergeant Joe England, who heads the section for the Tulare County Sheriff’s Office.

Whether it’s theft, vandalism or illegal dumping on farm property, “the farmer is often left to foot the bill,” England said.

For example, he noted, a theft of copper wire from an irrigation pump might bring the thief $50. But it results in $2,500 in damages to a farmer’s irrigation system.

Illegal dumping, like this pile of furniture and other trash beside a Kern County pistachio orchard, is one of the most common crimes against the ag industry (photo by C. Merlo.)


What’s Hot in Ag Thefts

While stolen truckloads of almonds or pistachios can make headlines, such high-profile cases aren’t what England and Stuhmer see on a daily basis. Far more common, they say, is equipment theft from farms and orchards.

“The bulk of ag crime is stolen ATVs, utility terrain vehicles (UTVs), ditch pumps, trailers, sprayers, tools, even farm trucks,” said Stuhmer.

Thieves often steal to get their hands on equipment metal, such as copper wire in irrigation pumps. But catalytic convertors are also a big market these days. Thieves can steal them in less than a minute and fetch $400 to $600 for each catalytic converter, according to Stuhmer.

“It’s a very easy, quick and lucrative business,” he said.

Common ag crimes also include illegal dumping, bee thefts, homeless camps in orchards, vandalism, fraud and embezzlement. Thieves will break into farm offices or trucks to steal the checkbooks they find there. They can create checks in their own names that way and cash them quickly. Sometimes they’ll engage in “check-washing,” which involves removing the original name from the check and replacing it with their own name. And, of course, if they find credit cards, they use or sell them.

Such crimes add up to “death by a thousand cuts for farmers,” England said. “It’s frustrating for them and for us.”

Sgt. Joe England with the Tulare County Rural Ag Crime unit, said this electrical panel box, which controls the almond orchard’s irrigation pump, could be a prime target for thieves seeking copper wire (photo by C. Merlo.)


From an Insurer’s POV

Law enforcement isn’t the only entity focused on stopping rural thefts. California-based The Zenith Insurance Company covers agricultural clients and offers coverage for insured stolen property. The company also has a risk management team that advises clients on how to better secure property.

Tractors, implements and nut-harvesting machines are common targets for thieves, said David Bente, senior ag material damage claims specialist for Zenith. Dollar losses can range from a few thousand dollars for smaller tractors and implements to $100,000 or more for shakers, harvesters and self-propelled carts.

“Many times, theft or vandalism is a crime of opportunity and access,” said Bente.

Equipment can be vulnerable to theft during harvest when it’s left overnight or on weekends in orchards, where it’s not secured by fencing or locked gates.

“We’ve seen equipment stolen from a field or orchard in one part of the state and located in another part of the state, sometimes within weeks, sometimes within years,” Bente said.
Bente and his Zenith team had a GPS unit recovered from a party who had it for sale on Craigslist, where it was being offered for about 10% of its actual price. Similar recoveries have occurred with ATVs and UTVs.

“Many times, when items are recovered and towed, we end up with recovery charges worth more than the items themselves,” noted Bente.

Dave Bente with The Zenith Insurance Company said theft or vandalism is a crime of “opportunity and access” (photo courtesy D. Bente.)


Working to Catch the Bad Guys

Not all online listings are stolen, of course. And the online platforms do work with law enforcement to help trace such postings.

“OfferUp has a special unit dedicated to stolen goods,” Stuhmer said. “We’ve had great success working with them to help figure out where equipment may be. Sometimes they’ll come to us if they suspect someone who’s selling something that might be stolen.”

Stuhmer said the recovery rate for stolen property depends on the area and reporting levels. “The national average for recovering stolen equipment is 20%,” he said. “But where there are ag crime units, the recovery rate is 40% to 50%. We pride ourselves on that and taking care of the ag community.”

Most stolen equipment is located within 10 miles of the original theft, Stuhmer added.

Bente said he currently has over 230 theft units, and the recovery rate is about 6%.

“I will say that with the help of the CRCPTF, the Sheriff’s Office, the California Highway Patrol and the information-sharing among everyone, recovery rates are getting better and better,” Bente said. “It’s great that we’ve been able to partner with all of them, sharing knowledge and learning from each other.”

Like many, Stuhmer is frustrated by the light punishment for ag crimes. Perpetrators often receive probation or small fines and rarely do jail time, he said, especially now that COVID-19 restrictions are limiting the number of inmates in facilities.

Detective Don Stuhmer, president of the California Rural Crime Prevention Task Force, often works with OfferUp to find stolen property that’s been posted on the online marketplace (photo courtesy D. Stuhmer.)


What You Can Do

To prevent theft and other criminal activity, Stuhmer, England and Bente urge growers to follow these tips:

Install power interrupt devices.

“Most equipment has a single key to start all equipment made by a manufacturer,” Bente said. “Many times the key is left in the ignition, hidden under the seat or in a cup holder.” That makes the equipment an easy target for theft. Bente advises his customers to install a battery interrupt or Perko® switch. This interrupts the electrical system, cutting power and preventing the unit from starting. Although many stolen units have a shut-off switch installed by the factory, too many owners and operators just don’t use it, he added.

Always lock vehicles, compartments, doors, windows and fuel and oil caps.

Install locking entry gates, yard fences, alarm systems and surveillance cameras to harden the target.

“We’d love for people to put an 18-foot wall around their property, but we know that’s not feasible,” Stuhmer said. But taking extra precautions can help deter criminal activity or help law enforcement find the perpetrators.

Add GPS tracking systems to equipment.

“We have a 100% recovery rate on stolen property that’s equipped with GPS devices,” said England.

Share your suspicions.

“If you see something that doesn’t look right, like taillights at night or unfamiliar tracks, let us know,” England said. “We can set up a patrol to keep an eye on your area.”

Report thefts and other criminal activity to law enforcement.

Stuhmer’s biggest complaint is the lack of communication between ag crime victims and law enforcement. “If we don’t know about it, we can’t do anything about it,” he said. “We need to know. If someone gets six convictions for grand theft, then they’ll see prison time.”

It may seem obvious but always lock vehicles left in the orchard (photo by C. Merlo.)

Growers Going Over-the-Top with Hazelnut Harvester

The rocky, river-bottom soil that Carter Clark’s young hazelnut orchard sits on is not conducive to conventional harvesting, and as trees were maturing, Clark was not looking forward to harvest. Fortunately, Andrew Herr, chief marketing officer of Littau Harvester, which is headquartered a couple of miles from Clark’s orchard in Stayton, Ore., offered Clark an alternative.

For a fee, Herr proposed, Littau could harvest the nuts with a mechanical blueberry harvester by going over the top of the young trees and catching the nuts before they ever hit the ground.

Clark jumped at the offer. The over-the-row harvester offered few drawbacks and many advantages, among them harvest timing. Because Clark didn’t have to wait until the husks released the nuts, he was able to get nuts to the processor a full 30 days ahead of most growers.

Then there is the speed with which he was able to complete harvest. “Whereas your traditional guys might be doing two to three sweeps during harvest, with the Littau harvester, you go over the entire row and you take every nut off that tree in one pass, and then you are done,” Clark said. “I started harvest on Sept. 1 and I was done harvesting my 30 acres on Sept. 2.”

Labor costs drop considerably with the over-the-row harvester, Clark said. And not having to prep the orchard floor prior to harvest is a huge advantage. “I can mow, say three times a year, with a rotary mower, and I’m not scraping. I’m not doing all the things you have to do to get that floor laser perfect.”

And despite that, Clark doesn’t believe food safety is a concern with conventional harvest, the idea that at some point in the future it could become an issue is something he keeps in mind. “Obviously, nobody eats the outside of a hazelnut,” he said, “so it may not ever be an issue to have nuts hit the ground, but it is something that people talk about.”


Still in Its Infancy

The idea of running a blueberry harvester over the top of young hazelnut trees was not new when Clark tried it. A few hazelnut growers had tried it in 2019 the year before he did. And Littau has even introduced an over-the-row harvester for tree fruits with a higher clearance that is now being viewed as an alternative for harvesting more mature hazelnut orchards. That harvester is available to rent from Littau.

Still, over-the-row harvest for hazelnuts is an idea very much in its infancy, Littau’s Herr said, albeit one generating considerable interest.

“I always get calls about it,” said Nik Wiman, Oregon State University Extension hazelnut specialist. “I think a lot of people are interested in it.”

Ryan Flaherty, grower relations manager for the farmer-owned co-op Hazelnut Growers of Oregon, posted a video on the social network platform LinkedIn earlier this year of the Littau ORXL harvester at work in a hazelnut orchard that received more than 30,000 views.

“It traveled the world,” Flaherty said. “I had people from Italy, Spain and Turkey reach out to me about it.”

Still, gaining widespread adoption of the practice has several obstacles, according to Wiman, primarily that hazelnut trees tend to get large as they mature, too large for over-the-row harvesters to clear, even the Littau over-the-row extra-large harvester, or ORXL.

“I know the OSU Hazelnut Breeding Program is looking at releasing some more compact trees that will remain smaller,” Wiman said, “but we don’t have rootstocks in hazelnuts like they do in tree fruits, where thßey can use highly dwarfed rootstock to create a smaller tree. There is some grafting going on, but it is not for dwarfing purposes, so that is kind of a missing link in the chain as far as being able to have a super-high-density orchard of smaller trees.”

One drawback to using the over-the-row harvesters in hazelnuts are husks still remain on nuts after harvest and must be removed at processing plants.


Hedgerow Pruning

Pruning trees into hedgerows under more dense plantings could offer a means to keep trees small, Wiman said.

“I think growers could successfully keep the trees relatively small with hedging,” he said. “And I definitely think there is going to be some movement toward that, especially because we are planting a wider variety of soil types with hazelnuts, including some that are not as productive as historically nuts were produced on. In those cases, the tendency is for growers to go to slight tighter spacings, with the assumptions that the trees are not going to reach the size they would on a different soil type.”

Clark noted that he is planning to do some hedging this year in hopes of keeping his trees smaller longer. “Maybe the orchard of the future is narrow, tight hedgerows, and you are running a machine over the top to pick them,” Clark said.

To date, however, most are looking at the over-the-row harvester as a short-term option, something to abandon once trees reach maturity.

Another hurdle to widespread adoption of over-the-row harvesting is that, unlike in conventional harvests where nuts release from husks before being swept off the orchard floor, with over-the-row harvest, husks have to be removed at the processing plant. “Removing that husk at the wash plant is a challenge,” Flaherty said.

Still, Clark said, he found that some processors were okay with removing husks as long as the nuts come into the plant early in the season.

“I think it is scary for processors, because it is so different,” Clark said. “But it seems like a few receiving stations have figured it out. It takes more work, but they are your first nuts in. You don’t have trucks sitting behind these nuts waiting to go, so you’ve got a little time to dial in your machines. And if you have to run them twice, well, they are probably the only nuts at your facility right then, so you have time to work with them.

“I think it would be a lot harder for the processors if these were mid- or late-season nuts coming in this way,” Clark said, “but because they are early, they have a little more flexibility.”


Tree Health

Another question still looming over widespread adoption of the practice is how the harvesters will affect the long-term health of a tree, and, more specifically, next year’s crop.

“That is another aspect to this that is not clearly understood,” Wiman said. “If you are knocking off a lot of catkins with the harvester, you have to wonder how harmful that is to your next year’s crop.”

Timing harvest in a way that maximizes yield is another issue yet to be fully understood, Wiman said. “It is efficient,” Wiman said of the harvester, “but there is a lot of crop that is knocked on the ground just by the fact you have this big machine going through the orchard and it can’t catch every nut that drops. That is another piece of the puzzle that I think needs to be figured out.”

Still, even with the unanswered questions and even provided that at least in the short term, use of the over-the-row harvester will be isolated to young orchards, with so many acres in the Willamette Valley at early stages, there is a huge potential for applying this technology, Wiman said.

Clark agreed. “In your first year of production, you are probably only going to get a couple of hundred pounds of nuts [per acre], and if that hits the ground, that is an awful lot of work for not much gain,” Clark said. “But if you can go through really quick with a Littau harvester and knock every nut off that tree, for the guys that already own that machine, I think that could make a lot of sense.”

Almond Irrigation Systems of the Future

Implementation of new irrigation system technologies and strategies is continuously on tree nut growers’ minds. Irrigation systems of the future will need to be nimble and flexible to deal with variability in the orchard for maximum water use efficiency.

Growers may look at water use as it relates to rate and timing, but there is another important aspect to consider when designing an irrigation system in an orchard, known as spatiotemporal variability.

Spatiotemporal variability may be caused by variation in soil physical and hydraulic properties, which affects soil water infiltration rates. Soils that have high spatiotemporal variability are said to be more heterogeneous, while those with low spatiotemporal variability are said to be more homogenous. Heterogeneous soils have areas of varying infiltration rates or soil water holding capacity.

It is the responsibility of the grower and/or irrigation system designer to account for spatiotemporal variability in order to meet engineering and horticultural requirements as well as maintain economic viability of an orchard, according to UC experts. They recommend that this variability be considered in future almond irrigation system designs as well as irrigating by tree variety and managing irrigation to optimize the orchard’s ability to provide agroecosystem services (e.g., improved soil health and water quality).


Account for Spatiotemporal Variability

Water stress in an orchard is not always due to low available water. Spatiotemporal variability and varying infiltration rates can also cause too much water to be present in certain parts of an orchard. UC Davis Associate Professor of Agricultural Water Management and Irrigation Engineering Isaya Kisekka explained reasoning for this issue in an Almond Board of California webinar in which he referenced research at CAPEX ranch in the Central Valley.

Kisekka explained why trees in a row were experiencing dieback when other trees on the same irrigation lateral appeared healthy. “The biggest problem is this particular ranch has low infiltration rates in some areas because the water, especially the surface water that they get, has very low electrical conductivity,” he said, “and from soil physics, we know that can create sodicity problems which result in low infiltration and drainage problems.”

How do growers and/or irrigation system designers design a system to address these problems? The answer, according to Kisekka, is a flexible system that accounts for soil type, infiltration rates and soil water holding capacity among other factors. Most importantly, irrigation zones need to be established based on where these characteristics differ in an orchard.

In a Kings County Farm Bureau webinar, grower Dino Giacomazzi of Giacomazzi Almond Company Inc., explained how he first approached variability when planting his almond orchards. “We went through a very extensive process of research, looking at every technology available,” he said. “We mapped all of our fields by soil type and designed irrigation sets based on the soil type. We engineered our systems so that our lateral pipelines and drip hoses followed the soil type contours.”

Giacomazzi said that the system was designed for short, high-frequency irrigation or long, low-frequency irrigation based on soil type. “After many years of implementing variable rate irrigation, we discovered that higher frequency irrigation worked well for all soil types,” he said. “We don’t tend to use the soil type zones anymore, but we do use our dual laterals to irrigate pollinators differently than Nonpareil going into harvest.”


Irrigate by Variety

Along with spatiotemporal variability, the different horticultural characteristics (crop water use, biomass accumulation, canopy structure, etc.) of varieties like Nonpareil, Butte and Aldrich affect overall water use efficiency in orchards. Kisekka recommends growers and/or irrigation system designers consider designing future systems based on varieties in rows to maximize this efficiency and improve production.

“It will be easiest if irrigation system designers can already design a system that allows a grower to control each of these rows or these different varieties independently,” he said, citing research on site-specific irrigation by variety that looked at the potential benefits to water use efficiency.

Kisekka noted that varieties like Nonpareil, Butte and Aldrich reach hull split at different times. “If all the trees receive full irrigation before hull split and then we start cutting back, there could be opportunities here to achieve some water savings and improve our irrigation water use efficiency,” he said. “The other benefit is to allow us to continue to irrigate the variety that has not yet reached its optimum harvesting time.”

In order to irrigate in this fashion, a flexible system is required. A system that would allow growers to continue irrigating Nonpareil trees during drying and before harvest of pollinators, according to Kisekka, is ideal.

Giacomazzi explained how his system for almonds is set up by variety to separately irrigate his Nonpareil and Monterey trees. “In our newer systems, we designed them for higher frequency irrigation and included separate laterals for Nonpareil & pollinators,” he said. “Rather than having lots of little valves like we have in our variable rate systems, we have gone to bigger sets, less hardware, more acres irrigated per hour. Our goal is to irrigate as many trees as possible as many times as possible in a single day.”

Zone irrigation system at the CAPEX ranch near Corning designed to allow flexibility in irrigation scheduling by grouping irrigation zones with similar soils into the same set (i.e., Blue: Heavy soil set, Green: Layered soil set, and Red: Light soil set).


Dual-Purpose Systems

Kisekka also stressed the need for the growers and irrigation system designers to consider other factors besides production within the agroecosystem when designing irrigation systems, such as water quality, soil health, reduction in greenhouse gas emissions and carbon sequestration.

“For example, we need to design systems that can provide water to both the tree as well as the cover crops in some areas where cover crops are proved to be viable,” he said, “because these cover crops have many benefits. They can improve soil health and they can also improve bee habitat, which is important for pollination.”

Kisekka recommends dual purpose irrigation systems with microsprinklers or a combination of drip and microsprinklers that can reach not only the primary crop but also the cover crop. Microsprinklers can also be used to aid in carbon sequestration of wood chips from whole orchard recycling by breaking the chips down, and recent UC Davis research has found that a 58% increase in total soil carbon is possible from chip incorporation in almond orchards.

Another area Kisekka said to consider is agricultural managed aquifer recharge, which concerns water quality and quantity and its success is closely tied to efficient fertigation during the season. “This goes to, again, thinking about a dual-purpose irrigation system,” he said. “So, you design irrigation systems that would meet crop ET but also can allow flooding of the orchard to recharge groundwater if flood waters exist.”

Irrigation Management to Reduce Hull Rot

Management of irrigation, including regulated deficit irrigation, is a proven option for managing hull rot in almond trees, according to UCCE experts and industry professionals.

Hull rot nicknamed the “good grower’s disease,” affects trees that are well irrigated and fertilized with nitrogen. “This is because the plant tissue itself is more vulnerable to infection,” said UCCE Orchard Systems Advisor in Madera and Merced counties Phoebe Gordon.

In a UCCE San Joaquin Valley Trees and Vines post, Gordon said to use regulated deficit irrigation (RDI) at hull split to induce moderate water stress on the trees. She recommends reducing irrigations by 10% to 20% in the first two weeks of hull split and resuming full irrigation afterward as to not stress the trees postharvest, noting that a decrease in next year’s fruit load can occur.

“If you have an orchard that is severely affected by hull rot, the small yield reduction via smaller kernels may be far outweighed by the avoidance of the loss of fruiting wood,” she said.

According to Wilbur-Ellis Agribusiness Technical Nutrition Agronomist Matt Comrey, growers can’t deficit irrigate without a good understanding of current water demand and how much water is being applied (application rate).

“Knowing those two items are critical in any irrigation schedule,” he said.

Correctly assessing current water demand is best done with a pressure chamber to measure plant stress, Gordon said. “Monitor stress with a pressure chamber; you should aim to keep the trees between -14 and -16 bars,” she said. “I’ve talked to a grower who let their trees get a little too stressed during this period and suffered a lot of sticktights, so again, induce RDI without using the pressure chamber at your own risk!”

Gordon agreed that monitoring plant stress without the use of a pressure chamber is risky. Soil moisture sensors often don’t provide accurate representations of an orchard due to variability in soil and water holding capacities and evapotranspiration is only an estimation of how much water trees have lost.

“I’ve heard performing reduced deficit irrigation without a pressure chamber as playing Russian roulette; you could get lucky and get it right, but things could also go very, very wrong,” she said.

Biologically Integrated Orchard Systems Field Day Aug. 27

Community Alliance with Family Farmers (CAFF) is hosting a free on-farm field day that will cover past and present research on the impacts of biologically integrated orchard systems (BIOS) in walnut. CAFF’s BIOS for Walnut project is funded by CDFA through their Biologically Integrated Farming Systems (BIFS) program, which seeks to explore alternative approaches to pest management in California cropping systems.

The field day, which takes place on Aug. 27 in Linden, Calif., will cover mating disruption, cover cropping, pressure chambers for water use efficiency, and soil testing.

CAFF’s Ecological Pest Management Program Specialist Hanna Kahl said field days are an important component in getting information out to growers.

“Scheduled field days are critical for highlighting the work of this program,” she said. “Field days provide an opportunity for collaborating growers to share their experiences and knowledge while demonstrating how these practices work in the field. These events also bring together growers and extension professionals in order to share and discuss challenges, research and best practices for integrated pest management.”

Kahl believes that growers will have more success in adapting these practices on their farms when they get a chance to meaningfully engage with the practices’ practical and applied aspects.

“Knowing this information will increase the tools available for farmers to address pest management challenges on their farms,” Kahl said.

CAFF’s field day, along with its ongoing research, focuses on mating disruption for management of codling moth and navel orangeworm. Kahl said that while some growers are interested in mating disruption and understand the potential benefits, many haven’t tried it in their orchards.

“We hope to provide an opportunity for these growers to test out mating disruption on their farms and provide assistance in understanding the effectiveness and economic feasibility of using mating disruption.

“We have continued to collect data on codling moth and navel orangeworm numbers in traps, number of dropped nuts, nuts in the tree infested with moth larvae, and costs associated with the use of mating disruption compared to the standard management approach on each farm,” Kahl said.

CAFF’s field day and ongoing research also looks at the use of biological control practices, including cover crops and the release of predatory mites, to manage web-spinning spider mites, according to Kahl. “Cover crops provide pollen and habitat that can increase densities of several predators, such as big-eyed bugs and minute pirate bugs,” she said. “Augmentative releases of predatory mites could further reduce mite densities.

“The effects of cover crops and release of predatory mites has not been examined thoroughly in walnut systems,” Kahl continued. “If effective, then this approach could be used as a sustainable alternative practice to manage spider mites in walnuts.”

According to Kahl, CAFF has established mixed cover crop plantings and released predatory mite species (Galendromus occidentalis and Neoseiulus californicus) into orchards and are sampling spider mites and their predators using sticky cards and leaf samples.

To attend CAFF’s upcoming field day and to find additional information about the event, visit the registration page.

Water Budgeting and Management for Pistachio in a Drought Year: What are the Options?

Low precipitation over the last year in the San Joaquin and Sacramento Valleys and long-term drought are forcing pistachio growers to make tough decisions for their irrigation management.

While pistachios are known for their ability to withstand drought, enough water stress can still cause high percentages of blanks, low shell splitting percentages and reductions in overall yield.

To mitigate these issues, UC experts recommend pistachio growers employ water budgeting strategies, monitor tree water stress levels and implement drought management techniques, such as proportional decreases in water application throughout the season or regulated deficit irrigation at different stages in crop development.


Water Budgeting

Water budgeting, along with soil moisture monitoring, helps to keep track of water depletion and eventually minimize water stress damage to tree health, growth and nut quality during normal years and drought. Daniele Zaccaria, UCCE agricultural water management specialist, said in a June 2021 UCCE In a Nutshell newsletter article co-authored by UCCE Farm Advisor Mae Culumber that a water budget considers the amount of irrigation needed to replace water losses from transpiration by trees and vegetative cover and evaporation from the soil surface, known in combination as crop evapotranspiration (ETc).

Irrigation is needed when the actual ETc exceeds water inputs and soil moisture storage. “They [growers] try to refill the soil profile every now and then, and then they keep showering a little bit of water to keep the soil moisture in the root zone pretty optimal. This is in a normal year,” said Zaccaria in an interview. “This year is not normal. They try to supply an adequate amount of water in the most sensitive stages and then reduce the applications in stages that are less or not sensitive to water stress.”

Under constrained water supplies during drought years such as this one, growers need to be strategic with their on-farm water allocation, and it has been shown that regulated deficit irrigation can result in improved water use efficiency without significant reduction in nut yields, according to Isaya Kisekka, associate professor of agro-hydrology and irrigation at UC Davis.

In pistachio, multiple UC studies have found that regulated deficit irrigation is effective in saving water without stressing the tree enough to adversely affect yields at harvest. “[In pistachio], there are sensitive and less sensitive stages,” Zaccaria said.

Sensitive stages for pistachio include shell expansion (Stage I), which occurs during the first two weeks of May, and nut fill (Stage III) beginning around late June, according to Zaccaria and Culumber. Pistachio trees can be moderately stressed through deficit irrigation during the shell hardening (Stage II), which occurs from mid-May to late June, and during postharvest without adversely impacting the final nut yield. Zaccaria explained that this is possible because pistachio yield is already defined on the tree.

“The yield is defined already in terms of the number of nuts on the trees, so it’s a matter of navigating and carrying that number of nuts up to the harvest with the largest possible kernel weight to obtain profitable yield,” he said, noting that improper deficit irrigation can lead to blanks, small nuts and/or dropped nuts.
Soil moisture monitoring also factors into water budgeting by letting growers know how much water can be depleted from the soil before water stress levels become dangerous as well as the amount of water infiltrating the soil root zone during and after an irrigation. The goal is to maintain water levels at all times between field capacity (where irrigation isn’t needed) and the management allowable depletion, which is the maximum amount of water that could be depleted at any given time without creating water stress conditions to plants that can adversely impact vegetative growth and yield (for nut orchards, the MAD is about 40% to 50% total soil available water.)

Water budgeting also requires knowledge of a site’s soil characteristics. Kisekka said that growers should know the water holding capacity of their soils by layer. The depth of soil considered for a water budget changes depending on the ‘effective rooting depth’, the portion of soil from which trees extract most of their water and nutrients. For pistachios grown with microirrigation, UC notes this is generally the top three feet of soil.

Depletion in the top three feet of soil should be tracked for pistachios as part of water budgeting. Kisekka recommends developing a checkbook spreadsheet to track water inputs (irrigation in summer months) and outputs (ET), and soil water sensors can also be installed to track soil water depletion.

“It is important to note that there is no sensor that directly measures soil moisture; they all measure a surrogate variable (e.g., the permittivity of the soil) and correlate that to soil moisture,” Kisekka said.

He said a useful technique could be to benchmark full and refill points for the variable the sensor is directly measuring without the need to do the conversion to soil moisture.

“[In other words], determine the permittivity value after irrigation or rainfall to set the full point and do the same thing to determine the permittivity value when the soil water is depleted and irrigation needs to occur,” Kisekka said.

Zaccaria said that when looking at soil-water interactions in the orchard, growers should also be aware of critical areas where water may move differently than others due to differences in soil texture. Paying attention to these variations, he said, can be beneficial to accurate water budgeting.

“You can optimize irrigation applications and probably save a little bit of water if you adjust the frequency of water applications to account and buffer for differences in soil texture [in critical areas],” Zaccaria said, noting that placing soil moisture sensors in critical areas of orchards will help with optimizing irrigation applications.

Newer tools for measuring SWP, such as this cosmic-ray neutron probe, appear promising for pistachio and other tree nuts (photo by I. Kisekka.)


Understanding Tree Stress

Irrigating according to a water budget and soil moisture monitoring does not provide information about how orchard trees respond to the applied water schedule, according to Zaccaria and Culumber. Older tools (pressure chambers) and newer tools (cosmic-ray neutron probes and automated osmometers) for measuring stem-water potential (SWP) offer a plant-based approach to understand if plant stress is within acceptable levels and when to trigger irrigation.

Kisekka and other UC researchers have recently found success with newer tools for measuring SWP over a broader area in the orchard. “Our recent research shows that you can use osmometers or micro-tensiometers successfully in some tree crops like almonds,” he said, noting that the technology is still being researched in other tree crops like walnuts and pistachios. “Also, other technologies that measure soil moisture of the entire orchard appear promising, and the orchard level soil moisture is correlated to SWP.”

SWP is measured in bars of negative pressure, which is compared to known values for water stress. According to In a Nutshell, the range of SWP for pistachio is between -6.0 and -20.0 bars, with pistachios in moist soil at field capacity having tree mid-day SWP values between -9 and -11 bars. Values more negative than -14 bars point to moisture stress that reduces growth and yield; however, UC research suggests the threshold for stress tolerance under regulated deficit irrigation may be between -15 and -18 bars at different stages of crop development.

Additional information about deficit irrigation and other mitigation strategies for drought in pistachio can be found in the June 2021 In a Nutshell newsletter for Tulare and Kings counties at cetulare.ucanr.edu/newsletters/In_a_Nutshell89801.pdf, and on the UC Drought Management webpage at ucmanagedrought.ucdavis.edu/Agriculture/Crop_Irrigation_Strategies/Pistachios/.

Walnuts, Navel Orangeworm and Ethephon for 2021

Navel orangeworm (NOW) continues to be problematic for California walnut growers. Jhalendra Rijal, UCCE area IPM advisor for Northern San Joaquin Valley, said NOW pressure varies among orchards, but with the drier winter and spring in 2021, as expected there has been increased activity with NOW in walnuts and almonds.

“From a walnut perspective, if you think about navel orangeworm right now (June), the flight may or may not matter too much unless there are blighted or codling moth-damaged nuts in the orchard,” Rijal said, noting that the third and/or fourth flight is a greater concern for walnuts at husk split.


Higher Pressures

“I would say that overall, the numbers and then the pressure are higher, but sometimes it may not mean too much,” he said, adding growers just need to wait, and watch, and see how that will relate in terms of the husk split timing.

The dry conditions in 2021 are certainly more favorable for survival of the NOW overwintering larvae whether the walnuts are on the tree or the ground, Rijal said, adding drier conditions probably play a role in overall NOW survival.

“We know navel orangeworm will overwinter in mummy nuts, whether it’s almonds, or walnuts, or pistachios,” Rijal said, adding rain in the wintertime likely has some impacts on NOW mortality.

Codling moth and blight damage in walnuts can leave openings for NOW for the first and second flights. An important management aspect of navel orangeworm in walnuts is to stay on top of these diseases and pests, Rijal said.

Nuts that have been damaged by walnut blight, sunburn, codling moth or have been mechanically injured are the nuts that the first and second flight rely on to build their populations, Rijal said.

“That is definitely the critical factor in terms of building navel orangeworm populations going into that third flight,” Rijal said.


Wait to Treat

For walnuts, the first two flights are not as significant as the third flight and the fourth flight for late season walnuts, Rijal said.

The third flight is of most concern, Rijal said, and timing of the flight and husk split is critical, which is why it’s important to track NOW flights.

If there are almonds or pistachios nearby, this can increase the pressure as all of them are hosts for NOW. “They (NOW) can move from one host to another host when they have the opportunity,” he said. “If you have an almond orchard next to a walnut orchard you’ll likely have more navel orangeworm flying around in the area compared to not having that.”

“It is not recommended to apply insecticides against navel orangeworm for the first and second flights,” Rijal said, adding these flights aren’t damaging to healthy walnuts.

“I would say that it’s not worth the money or effort to do an insecticide spray before that third flight,” he said, unless the grower has had consistent NOW pressure and damage in previous years.

Using chemical applications when needed is an important part of preventing resistance from building in all nuts as very limited insecticide active ingredients are available to use, Rijal said.

“We want to save those materials for the late-season window when the walnuts are susceptible,” Rijal said, plus it’s more economical, too, as these aren’t inexpensive materials.


Cultural Control

Winter sanitation is the best cultural control option at this point for managing NOW. Going into the season with a clean orchard means there will be less NOW pressure at the start of the season and less in-season, too, Rijal said.

It’s not just the nuts on the tree, but also the nuts on the ground that need to be removed, Rijal said.

“If navel orangeworm could not find mummy nuts or damaged nuts to lay their eggs, they lay eggs on the nuts that are still on the ground,” he said.

“Early harvest is also a very good tool, especially when there is late season harvest and harvest is dragged out for a longer time,” he continued, adding an earlier harvest could protect the nuts from later generations of NOW damage.

For early harvest, Ethephon can be used in walnuts to advance and synchronize the harvest, and it should be helpful when NOW populations are high. Ethephon should be applied at the right stage of the walnut maturity. UC IPM Guidelines recommend applying 10 to 14 days before normal harvest for one shake walnuts (www2.ipm.ucanr.edu/agriculture/walnut/Using-Ethephon/).

An earlier harvest can potentially prevent damage from the third and fourth flights of NOW, Rijal said.

“Ethephon may not be for everybody,” Rijal cautioned, adding if the trees are stressed and are in poor health, or if the variety itself has a synchronized split, then an Ethephon application may not be necessary.


Mating Disruption

Mating disruption is also part of NOW management. Rijal and David Haviland, UCCE entomology farm advisor in Kern County, did research on mating disruption in almonds up and down the San Joaquin Valley.

This has helped increase mating disruption adoption in almonds and pistachios, Rijal said.

“We have not seen that level of adoption in walnuts,” he said, adding there could be other factors like price or the fact that walnut trees vary in size and variety, relatively smaller blocks, etc., but mating disruption is an important tool for the integrated management of NOW in walnuts, too.

Sterile insect release is another potential tool that growers might be able to use as a part of their NOW program. All nut crops are investing in research to look at the sterile insect release technique as part of an IPM tool for NOW management. However, it may take several years to develop these kinds of techniques and apply them to a real field scenario.

It’s been said time and time again, but there is no silver bullet to manage and control NOW, Rijal said, and he doesn’t see a single solution for management.
“It still will be part of the integrated pest management,” he said.

With over 2 million acres of almonds, pistachios and walnuts, plus other hosts, and multiple generations of NOW throughout California, we all know this pest is a challenging one, Rijal said.

“With the global warming and the expected increase in temperature, we’re expecting to have a consistent fifth flight in some of the southern San Joaquin Valley counties as early as 2040 based on a recent study.”

For more information, go to sciencedirect.com/science/article/pii/S0048969720361866.

“We all want a sustainable, long-term industry. The objective of the industry is to keep it sustainable for a long time, and for that, we need to adopt tools and techniques in a combined system so we don’t rely on one tool,” Rijal said.

Cover Crops in Walnut Orchards

A steady rise in intentionally planted cover crops in walnut orchards has been noted by UCCE Advisor Emeritus Joe Grant, who now serves as production research director for the California Walnut Board.

“There has been a steady increase each year of growers who start, intentionally, to have cover crops in their orchards.” Grant said. “There has been more promotion of this practice recently.”

Just allowing a crop of winter weeds to germinate and grow in the orchard won’t provide equal benefits to a chosen and planted cover crop. Large weeds can become problematic by spreading into tree rows.

Young walnut orchards can benefit from a planted cover crop due to its value as a green manure. A big driver of increased cover crop use, Grant said, is the goal of improving water penetration in the orchard. Cover crop decomposition adds organic matter to the soil, aiding water infiltration and water holding capacity. Cover crops can help prevent soil crusting by protecting the soil surface from the impact of sprinkler droplets and help improve traction and reduce compaction from machinery used in the orchard, especially in the winter.

Depending on the species in the cover crop mix, the plants can extract nitrogen not taken up by the tree and convert it to more stable organic forms. Cover crops can take up excess water from winter rains. Cover crops can also reduce erosion on slopes and areas subject to flooding and remove excess soil from winter rains in the spring when it can increase the risk of soilborne disease problems.

Cover crops can help with dust control, improving soil structure and protecting soil from wind.

Even with all the promoted benefits of a cover crop in a walnut orchard, Grant said that establishing fall-planted cover crops can be challenging and requires pre-planning.

“These cover crops need to be planted right after harvest, and the later varieties of walnuts like Chandler bump right up against cover crop planting time,” Grant said.

This annual reseeding brome cover crop in a Sacramento Valley walnut orchard is a system used in non-cultivated orchards (photo by Janine Hasey, UCCE Emeritus.)

In mature orchards, lack of sunlight and leaf litter on the orchard floor can interfere with stand establishment. If the orchard floor is dry at planting and no rain is in the forecast, irrigation may be required for germination.

Water use by a cover crop will increase the total orchard water requirement. In the spring, cover crops deplete stored soil moisture from winter rains. A UCCE cover crop guide for walnuts notes that a typical 5,000-pound-per-acre (dry weight) cool-season green manure cover crop can consume as much as about 180,000 gallons, or 6.5 acre-inches, of water.

There is also a risk of spring frost damage to young trees when a cover crop is grown in the orchard. A bare orchard floor absorbs heat during the day and releases it at night, but a cover crop reduces this heat absorption. This risk can be mitigated by mowing the cover crop well in advance if a severe frost event is forecast.

Cover crops can also interfere with spring orchard sanitation and orchard pruning operations. Destroying mummy nuts on the orchard floor to control navel orangeworm may require mowing the cover crop and decreasing its ultimate biomass production.

In orchards with pocket gophers or voles, cover crops may aid in increasing their populations as gopher mounds can become hidden from site and vole runways can be sheltered.

Population dynamics of three nematode species that attack walnut, ring nematode, root knot nematode and root lesion nematode may be affected by planting cover crops. Research shows that nematodes are less active in cooler months, and mowing or disking a cover crop by mid-May could limit their potential for harm. Sampling soil for nematodes pre-plant can help with cover crop planting decisions.


Choosing a System

Three cover crop systems have been used successfully in walnut orchards. These systems all have potential benefits as well as drawbacks to consider when choosing cover crops to meet needs in different orchard situations.

The first is a winter green manure crop that usually consists of large-seeded cereal grains and one or more nitrogen-fixing legumes. This crop is newly seeded each year in the fall and mowed or disked in the spring. This system fits especially well in cultivated orchards as the fertility benefits are maximized with the crop residue incorporated in the soil. If there is adequate soil moisture in the fall, this system may not need additional irrigation for germination and growth.

Annual reseeding legumes, including common vetch, subterranean or crimson clover, bur medic or grasses (Blando brome) are planted in the fall and managed during spring and early summer for seed production to allow for reestablishment in the fall. This system can only be maintained in non-cultivated orchards. It may also need irrigation if fall and winter rains have not provided adequate moisture for good growth.

Perennial sods include grasses such as perennial ryegrass and various fescues and/or legumes. The species are planted in fall through spring and mowed to maintain a year-round orchard floor covering. Irrigation beyond what is needed by trees is needed to maintain good growth.

Grant said there is an additional spring-planted cover crop strategy that includes warm-season species, such as sudan and cowpea. These species are helpful in increasing soil organic matter and improving tilth and water holding capacity, particularly in sandy soils. Their main drawback is increased water use and potential to contribute to nematode populations.


Planting, Management Strategies

To maximize their benefit, cover crops should be planted in as wide a strip as possible.

To maximize efficiency, the width of the planted strips usually matched the width of cultivating, seeding and mowing equipment advised. Planting with a no-till seed drill helps minimize disturbance on the orchard floor. Drilling seed also involves less ground preparation that broadcast seeding and is a more precise operation.

Removal of green manure cover crops is done by disking in cultivated orchards. A heavy crop can be mowed prior to disking. Flail or rotary mowers are used in non-cultivated orchards. Annual reseeding cover crops should be mowed to a half inch to one inch in height to reduce competition from winter weeds. The grasses in this type of cover crop do not tolerate the short mowing as well as the clovers. A second and final mowing is done in early to mid-June once seed has fully matured to ensure satisfactory reestablishment of the cover crop the following winter. A successful stand can be reestablished if half or more of plants in the cover crop produce mature seed before they are removed by mowing or disking. Mowing more frequently delays flowering and seed development by most annual reseeding species. Mowed residue left on the soil surface helps suppress summer weeds and will decompose by harvest.

Perennial rye and fescue mix improve orchard access by equipment in winter and reduce dust but require full-coverage or nearly full-coverage irrigation and at least some direct sunlight during the day in order to persist for multiple years (photo by J. Grant.)

Biological Control of Navel Orangeworm in Tree Nut Orchards

University of California researchers have been evaluating the role of biological control of navel orangeworm (NOW) in California for nearly five decades. This includes efforts since the 1970s to document the impacts of native predators and parasitoids on NOW control, and to find new parasitoid species to import and introduce. In general, biological control for NOW has had a secondary role in IPM programs, with cultural and chemical controls, including mating disruption, taking the lead. However, as broad-spectrum insecticides become more and more obsolete within almond and walnut production systems, and as producers of all nut crops embrace reduced-risk technologies like mating disruption, opportunities for biological control to play a role in integrated pest management programs are on the rise.


Early Research

Two UC researchers were key in the initial development of NOW biological control in the 1970s: Dr. Leo Caltagirone at UC Berkeley and, later, Dr. Fred Legner at UC Riverside. Both Caltagirone and Legner worked closely with UCCE farm advisors and staff and students at the former Division/Center of Biological Control (UC Berkeley) and Department/Division of Biological Control (UC Riverside).

Caltagirone’s initial efforts were to document the natural enemies already present in California that attacked NOW and the closely related carob moth (Ectomyelois ceratoniae). The egg parasitoid Trichogramma californicum was found as well as a number of larval parasitoids including the bethylid Parasierola breviceps, the braconids Habrobracon hebetor and Phanerotoma, the ichneumonids Venturia canescens and Mesostenus gracilis, and the chalcidid Spilochalcis leptis.

Caltagirone also documented a number of predators, including green (Figure 1) and brown lacewings and lady beetles attacking the moth’s larvae, and predaceous mites and the mirids Phytocoris relativus and P. californicus attacking the moth’s eggs. Unfortunately, all of these parasitoids and predators attacked a wide range of prey, and none were specialized enough on NOW to seriously drive down populations. As such, NOW persisted as a pest, and a classical biological control program was initiated with the goal of discovering more specialized natural enemies that had more closely coevolved with this pest in its native range, and therefore better adapted to naturally maintain NOW at densities below economic injury thresholds.

Caltagirone reported that NOW seems to be native to Central and South America; his surveys in the late 1960s to 1970s found it widespread in northern Mexico, and NOW was reported as far south as Peru, central Argentina and Uruguay. Today, it has extended its distribution to the southern U.S., across the south from California to the east coast and as far north as North Carolina. The first damaging infestations in almond and walnut crops were encountered in the 1950s, but through the 1960s, damage was relatively mild, typically <2%, until the late 1970s when damage of untreated populations was ~10% of Nonpareil almonds.

Caltagirone focused his exploration efforts in southern Texas and northern Mexico, where he discovered the encyrtid Copidosoma (=Pentalitomastix) plethorica, which had never before been described (Figure 2). This parasitoid has a very interesting biology in that the adult wasp puts an egg into the NOW egg, but the parasitoids emerge from the last stage of the moth larvae; in fact, hundreds of parasitoids emerge from a singly parasitized NOW larva. This wasp is ‘polyembryonic’ where the parasitoid egg hatches and forms a ‘polygerm’ of genetically identical embryos from a single egg through clonal division, basically like identical twins but hundreds of them. Following this discovery, in the 1960s and 1970s, the UC Berkeley laboratory produced millions of these wasps and released them throughout the Sacramento and San Joaquin valleys. The parasitoid established in California and is still found today, but is more common in the Sacramento Valley than in the San Joaquin Valley.

Figure 2. Copidosoma plethorica is a ‘polyembryonic’ parasitoid, meaning that one egg in the navel orangeworm host (inserted in the moth egg as shown in the upper left insert) will divide into hundreds of identical offspring. The wasp was imported from Mexico in the 1960s to help control navel orangeworm.

Shortly thereafter, Dr. Fred Legner focused his efforts to find a parasitoid in Uruguay and central Argentina as well as supplemental collections in southern Texas. Working with regional entomologists, he discovered another previously unidentified parasitoid, the bethylid Goniozus legneri (named after Legner) in Uruguay, and also imported the closely related G. emigratus from Texas. These bethylids also have a unique biology as described in Figure 3. Goniozus legneri is perhaps the most commonly found NOW parasitoid in California today.

Other natural enemies imported during the 1970s and 1980s include the egg parasitoid Trichogammatoidea annulata from Argentina, which in augmentation studies reached parasitism levels of 20%. The larval parasitoids Phanerotoma flavitestacea from Israel and Diadigma sp. from Australia were also imported and released, and while they reached parasitism levels up to 25% during the release trials, they did not overwinter well in California and are rarely found attacking NOW today.


Evolving Biologies

While these natural enemies and others are still working in California’s tree nut crops, they still do not singularly or collectively provide control levels acceptable to most growers. Part of the issue is their biologies that may have evolved to satisfy their own survival rather than the control levels needed by modern growers, especially in the face of strict aflatoxin regulations. For example, the two most important imported natural enemies, C. plethorica and G. legneri, have biologies that allow them to make the most use out of a single host rather than search and kill many hosts.

Copidosoma plethorica is polyembryonic, so finding and parasitizing a single moth egg can lead to up to 800 offspring, but it is still only killing one moth egg. This species is easy to rear in the laboratory, but in the orchard, it is dependent on the ready presence of moth eggs to continue to reproduce, and in periods without eggs present or at low host densities when the adult wasps cannot find an egg, their numbers decrease.

Similarly, G. legneri puts many eggs on a single host larva, but the adult wasp has a behavior called ‘brood guarding’ where she will not attack and deposit eggs on a host and then go out and search for an anther host; rather, she will stay by her eggs and protect them from other G. legneri (that will kill her eggs and deposit their eggs on a host – or fight off other predators like green lacewings as seen in Figure 3.) For this reason, G. legneri does well when the NOW density is high, say 20% nut infestation, and you might have 20% to 40% parasitism levels in October after harvest. This is because the high pest population presents a target-rich environment where a female G. legneri can find and guard many NOW that are close together, but as the pest density lowers, parasitism levels seem to drop as well, and at current thresholds of <2%, it is often difficult to find a G. legneri in the orchard. Legner had suggested one practice might be to leave some nuts on the tree during the winter, but research in the 1990s showed that this leads to more NOW than G. legneri because the parasitoid overwinters as an adult and, as a result, does not need to have the mummy left in the orchard.

Figure 3. The Goniozus legneri adult female (A) approaches the moth larva, usually from the back or side, and then (B) mounts the larvae as it wiggles to free itself and moves towards the larva’s head where it injects a venom to paralyze the moth. It then walks up and down the host larvae (C) to ‘measure’ its size to determine how many eggs to attach, often biting the moth larva to ensure it is paralyzed (to the left of the wasp is an egg and there are five other eggs visible on the moth larvae.) The wasp larvae then develop as an external parasitoid (D) on the moth larvae, feeding there until they pupate and leaving nothing but the moth head capsule.

As mentioned, if you have NOW in your orchard, then these natural enemies are probably in your orchard at some level. Researchers are currently looking at ways to improve sustainable NOW control through manipulating ground cover management that may protect pollinators and enhance these natural enemy populations. While cover crops can be useful in some cropping systems, the addition of ground covers in tree nut orchards may not necessarily address the key bottlenecks currently limiting the impacts of natural enemies on NOW.

Surprisingly, one of the most overlooked of these predators, the common resident green and brown lacewings, might be the most stable and persistent of the resident and imported natural enemies. The green lacewing is commonly one of the more resistant natural enemies to different pesticides, and because they are generalist they are often found in the orchard at low or high NOW densities. Moreover, reported populations of NOW in Argentina and Chile never seem to reach damaging populations, and this does open the possibility to some other control agent out there that has yet to be discovered.

In California tree nuts, a great deal of effort has been made to identify and evaluate potential biological control agents for NOW, but up to this point, the role of biocontrol has been secondary to the use of winter sanitation, insecticides, timely harvest and mating disruption as the primary components of an IPM program. However, as growers shift away from broad-spectrum insecticides and embrace reduced-risk, selective chemical control programs for NOW, husk fly, scale, aphid and mealybug pests, it is anticipated that biological control organisms will have increased opportunities to become established and assist with NOW management programs. Information regarding the short- and long-term impacts of chemical control pests for almond, pistachio and walnut pests can be found within the ‘Relative Toxicities of Pesticides to Natural Enemies and Honey Bees’ tables in the corresponding UC IPM Pest Management Guidelines for each commodity at ucipm.ucanr.edu/agriculture.