by Thomas Grandperrin
Published on March 18, 2021
When trying to limit reliance on conventional pesticides, it is fundamental to take a more holistic approach and understand how to integrate all of the different tools available to develop a successful pest management program. Mating disruption is a proven technology that has gained a lot of popularity over the world in the past few years and is highly complementary to augmentative biological control.
I reached out to Emily Symmes, an entomologist currently working as a senior manager of technical field services at one of the world-leading companies in this space, Suterra.
Prior to her position at Suterra, Emily was an area integrated pest management (IPM) advisor in the Sacramento Valley as part of the University of California (UC) Cooperative Extension system. In addition, she served as the associate director of agriculture for the UC statewide IPM program, where she participated in their online pest management guidelines and coordination of their IPM advisors statewide.
Emily Symmes, senior manager of technical field services at Suterra
While her main focus during her career has been on the nut crops, namely almonds, walnuts, and pistachios, it increasingly spread to other systems for which both mating disruption and monitoring tools are used: grapes, citrus, pome, and stone fruits.
During our conversation, she told me more about the use of mating disruption on the US West Coast, gave some advice on the use of insect traps, and expressed her opinion on the future of augmentative biological control in nut cropping systems.
Mating disruption, an increasingly popular tool in nut crops systems
Mating disruption is being used for a vast number of pests around the world. In the United States, and more specifically in the California-Pacific Northwest area, the primary mating disruption products used in nut systems are for navel orangeworm (NOW) and codling moth (a walnut pest also affecting apple and pear orchards).
Emily expands on the principle of mating disruption, “The mode of action is to block the male ability to find the calling female. As a grower, you want to get the pheromones in the environment whenever that mating is active. You’re not going to have a knockdown effect like you would with a contact insecticide or a broad-spectrum contact insecticide, where you would expect your trap numbers to go way down the week following a spray because you’ve had this contact lethal impact. What you’re doing is blocking matings and you’ll see the impacts in the subsequent generations. That’s how all mating disruption works, by reducing population growth rate, which in turn can also allow other inputs like insecticides and biological control have a greater impact in preventing crop damage.”
Depending on the crops, orchard characteristics, and grower preferences, there are different “platforms” or ways that growers can get the mating disruption pheromone blends into the environment.
She explains that, “For growers and PCAs in the nut systems, aerosol-based Puffers are probably the most recognizable technology used to deploy the pheromones. We also have a microencapsulated sprayable formulation, which can be timed more specifically to certain insect flights and used throughout the year in more of a conventional approach since it’s sprayable. Then we’ve got dispensers that usually look like small cards and are hand applied. Depending on the pest, we have one or more available platforms. For example, for navel orangeworm we have both an aerosol and a sprayable. For codling moth, we have an aerosol Puffer, a sprayable, and a dispenser platform. There are lots of different options for growers to choose what best fits their particular crop system, their orchard, their needs, and their operations with regard to labor and other factors.”
Suterra is also looking at drone applications of the sprayable pheromones. This could help when there aren’t enough sprayers available for the amount of acreage to cover or when tractors cannot access the field because of terrain or environmental conditions.
One of the big benefits of the sprayable pheromone approaches, as opposed to sprayable insecticide approaches, is that the pheromone doesn’t require full coverage, unlike a miticide or an insecticide. Growers don’t have to hit every single row, drive slowly, or use large water volumes to get the pheromone molecules active in the environment.
Mating disruption: a multi-year approach
Like most of the alternatives to conventional pesticides, some growers might believe that mating disruption will cost more, however most mating disruption product costs are on par with many of the newer generation selective insecticide chemistries. Emily cautions growers “not to try to look too individually at each of their IPM inputs because it’s really hard to separate them”. Emily also advises them to look beyond the efficacy on the targeted pest. “Pyrethroids are quite inexpensive, and when there’s no resistance, they can be effective if timed pretty well. But they have unintended consequences, like blowing up the spider mite populations by adversely impacting natural enemies, which in turn might increase the need for more miticide applications. We have to look at the costs/benefits in a comprehensive way.”
It is not always easy to decide whether mating disruption can allow for reduction in pesticide applications, especially for a pest like navel orangeworm. “Ecologically speaking, it is a moth that can migrate fairly significant distances, and because we have the risk of aflatoxin contamination, the nut industry standards for damage are really low. So I think that we’re very cautious when we’re starting to think about taking away inputs like insecticides for the control of NOW, even where mating disruption is in place and working very well.”
Even if it is still early to quantify the potential overall diminution of sprays, mating disruption improves the efficiency of the combined control measures and might be partially responsible for the movement away from broad-spectrum insecticides like pyrethroids to control NOW. Some softer novel insecticide products are more frequently replacing them, such as chlorantraniliprole and the insect growth regulator methoxyfenozide. The introduction of these new products has several advantages. They allow a greater rotation of active ingredients, mitigating the development of resistance. They are also softer on beneficial insects and predatory mites, opening the door to preventative augmentative biological control programs, and thus giving growers the ability to implement a truly integrated pest management program.
For nut growers wondering about the long term potential of mating disruption, it is interesting to look at crop systems and pests for which mating disruption has been used many years and is now a baseline of a pest management program. Examples include codling moth control in the Pacific Northwest in apples and pears and control of the Oriental fruit moth in peaches in California. Emily states that, “you can see a downward trend in insecticide use in those systems.”
In the future, Emily would like to see more long term studies on the impact of mating disruption on the reduction of pesticide use. “We need to look at all of the different facets of IPM, which includes mating disruption, but also natural enemies, sanitation practices, selective pesticides…and start analyzing when we can start to peel back on the spray program.”
Emily cautions growers and PCAs not to peel back on mating disruption. “Once you’ve got it in place, it really does start to “amortize” over time. Every additional year you’re driving populations down lower and lower, so your return on that investment increases every single year that you have it in place.”
Misconception and tips on the correct use of insect traps
Pheromone traps are well adopted by IPM practitioners. To ensure their proper use and that growers’ expectations are set properly, Emily explains some of their advantages and limitations when used in parallel with mating disruption.
“Within a mating disrupted environment, the ability of a male pest to locate the pheromone trap is severely inhibited, so not many will be caught. This actually is a good thing because it gives us a tool to monitor and troubleshoot whether the pheromone is actively working in the environment. What it does take away, however, is the ability for PCAs to track flights and abundance because very few to no moths are caught in the environment. The good news around that is, there are other tools that we can use to help track the pest populations.”.
Much like the pest control aspect, a holistic approach must also be taken within monitoring, considering all of the available pieces of information.
For navel orangeworm, other types of traps can be used in concert with the pheromone traps. Emily explains that, “With female-based traps, the female won’t be altered in her ability to find the traps in mating disruption orchards because the bait is comprised of components that mimic egg-laying substrates, not pheromones. Female traps can be either egg traps or those that catch adult moths. The bait for each of these are based on ground almond or pistachio, or a combination of the two. These tend to be less sensitive relative to pheromone traps in terms of the total numbers captured and active range, but they still provide valuable information. There’s also a phenylpropionate (PPO) lure that has shown good efficacy in mating disruption orchards for NOW and it catches both males and females. It allows growers and PCAs to track flight timings, get a relative idea of the population level in the orchard at different times of the year, and react accordingly.”
Emily checking a NOW egg trap (Credit: Kathy Coatney)
Traps give growers the ability to track the cycle of the population and can help determine the best time to apply any supplemental insecticides or sprayable flowable mating disruption product, but she advises growers not to over-rely on them to make the decision of whether or not a treatment is needed.
“There are very few instances where we’ve got really good scientific correlation between a number of pests in a trap and ultimate crop damage that would tell you in a very accurate manner that if you catch this many moths per trap in a week, that’s your trigger that you need to spray. In many cases, this type of decision making has to take into account a number of different pieces of information that collectively can indicate the need to treat and help you time the treatments.”
Augmentative biocontrol in almonds, walnuts, and pistachios
Mating disruption is a tool that should be used in a more holistic approach to farming which integrates multiple practices and techniques. Leveraging and preserving naturally occurring enemies (also called conservation biological control) or releasing commercially reared ones (often called augmentative biological control) are some of those additional practices.
“When it comes to the nut crops in recent history, practices have really centered around a conservation biological control approach,” Emily remarks.
This starts by monitoring and identifying the biological control agents naturally occurring in the field and the impact they are having on their targeted pests. Then it is important to know how to preserve them by minimizing insecticide inputs, choosing selective chemistries, and applying them in a manner to minimize detrimental impacts on natural enemies.
“That said, I really think that it’s worth revisiting the concepts of augmentative releases within nut crop systems.”
She relates that an independent PCA who was relying on biocontrol in the seventies but then went away from it commented to her that, “We need to start looking at augmentative release again to help control navel orangeworm and other nut pests.”
Emily explains that a lot of the research on augmentative biological control dates back to when nut growers were using a more broad-spectrum approach for pest management, which don’t necessarily work well with augmentation. This would explain why this type of research has become quiet. “A grower perhaps would invest in the purchase and release of natural enemies, but then they would have to come in with broad-spectrum sprays and end up wiping out their investment.”
But with the shift towards mating disruption and the use of more selective insecticide chemistries, Emily believes it is really worth taking a look at augmentative releases of natural enemies. “For spider mites, we’ve got different predatory mites, and six spotted thrips now, that can be purchased and released.” She mentions that some navel orangeworm parasitoids, such as the Goniozus legneri wasp, are also commercially available.
She elaborates on experiments and trial work that she has performed both during her previous assignment at the University of California or now at Suterra. “At the end of every harvest, we’ve been collecting nuts off the ground and cracking them open to look for damage and navel orangeworm infestation. Over the last four seasons, I’ve seen more parasitized navel orangeworm larvae than I’ve ever noticed in the past. I think that the shift toward mating disruption and selective insecticides has allowed the naturally occurring populations in the environment to persist and rebound to some degree, so we are observing more parasitism in recent years.”
Parasitized NOW larva (Credit: Emily Symmes)
Emily is eager to see more studies on this topic, to assess if augmentation release could allow more parasitization at an economically available cost for the grower. “I think that’s a possibility, especially now that we have better technology, such as drones, to release the beneficial insects.”
She admits that for pests such as navel orangeworm, mating disruption and augmentative biological control are longer-term approaches, but it is important to begin to adopt these methods now to get ahead of upcoming regulations and issues such as pesticide resistance. She believes that “it is important that we aren’t over-reliant on a pesticide-only approach. Growers should consider making these initial investments in longer-term sustainable pest management, and consider other ecological population reduction practices that are based on the innate pest biology. Learning how to make these work for the specific characteristic of their orchards and operations is also an important factor in easing the transition to new IPM practices.”
She comments that there is experimental data for other pests in nut systems that show that those alternatives can work effectively. Some California walnut growers for instance use mating disruption combined with augmentative releases of Trichogramma parasitoids to control the codling moth.
Why growers should experiment more and get ready for upcoming regulations
To conclude our discussion, Emily recommends growers and PCAs that are considering implementing mating disruption or biocontrol augmentation to continue to increase their knowledge base thanks to the wealth of available resources provided by the University of California extension system and commodity boards. She also suggests reaching out to education forward industry companies such as Suterra or UAV-IQ that want to help them “get the best bang for their buck” during the implementation of those new practices.
But she also emphasizes that nobody knows the orchard better than the grower and their PCAs. So she’d like “to empower them to experiment more within their own system and operation, as certain things work better in certain places and not as well in certain places. They can really be their own scientists and develop their own personal case studies for what pest management strategy works the best in their unique circumstances.”
As a closing remark, she advises growers to get ready for upcoming regulations. “We are losing tools in the toolbox. Even if, as a grower, you don’t feel that is something you need or is a fit for your operation in the short term, having those alternative pest management practices available and understanding them, puts you in a much better position to react and make those decisions when it’s time.”
Do you have experience with the implementation of mating disruption or augmented biological control in nut systems? Reach out to us, we’d love to hear your story!
UAV-IQ is helping organic and conventional growers implement biocontrol in an efficient and cost-effective manner by using drones to release beneficial insects exactly when and where they’re needed to suppress pests.
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