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Decades ago, when tighter restrictions began to curtail tree nut growers’ use of broad-spectrum pesticides, chemical companies developed more targeted and selective chemistries for control of insect pests in their orchards.
While the newer chemical alternatives to broad-spectrum pesticides usually cost more per acre to apply, they are generally equally effective if applications are timed to target the intended results may take longer to see because these pesticides target eggs, larvae or nymphs rather than adults. Resistance issues remain with most newer chemistries, but they can preserve beneficial insect populations and potentially lower overall control costs.
Almond grower Donny Hicks agrees. He said if a grower can use a product that will target the desired pest and will not harm the beneficials in the orchard, they will use it even though it may cost more. An example would be navel orangeworm control and using a softer material instead of a pyrethroid to help avoid mite flareups during the summer.
Pyrethroid products still have their place in tree nut pest control, John Post said. These products can be used to “spike” an application of a more selective material, with the aim of killing adult stages of pests like leaffooted bugs.
“They are cheaper to use, and we will use lower rates to prevent flareups of mites and preserve beneficials,” he said of broad-spectrum pesticides.
He added that this strategy has worked the last couple of years. If mites start to flare, they will have to switch over to the more expensive products that are safer on the beneficials.
Post said selective pesticides typically target precise species or a generational stage of an insect or disease.
“Due to this, you many times need more pesticide chemistries in a single spray program to get everything you need controlled,” he added.
Spray Coverage Is Important
Good coverage is more important with selective pesticides. Post said it is more important because these materials are targeting different life stages.
For example, the FMC product Altacor targets egg stages, particularly at or before egg deposition, providing ovicidal activity and controlling newly hatched larvae. It works on key pests such as codling moth and navel orangeworm by causing feeding cessation upon exposure.
Timing of application is also critical. To be effective on eggs or other life stages, scouting or using degree days to determine when to target a specific life stage is important, Post said.
Improving spray effectiveness is not just about timing. There is also the cost of the more selective materials. Post said research trials conducted by Ag Advisors showed that how the material is delivered makes a difference. Slower speeds and spray nozzles that are not worn out improve coverage. The trial showed that spraying at 2 mph compared to 3.1 mph results in significantly improved coverage, particularly in the upper canopy.
Post said weighing the economics of reduced edible meat yield caused by insect damage justifies the costs associated with better coverage.
There can still be pest resistance issues with newer chemistries. When it comes to tree nuts, pyrethroids have been the only viable option for control of leaffooted and stink bugs, and there is evidence of resistance. Efficacy of selective chemistries has also been reduced due to resistance.
Post said he avoids using the same product on the second generation of pests, including the industry standards Altacor and Intrepid.
“If a grower can use a product that targets the pest without harming beneficial insects, they will use it even though it may cost more.” – Donny Hicks, almond grower
Preserving Beneficial Insects
Juan Lumbreras said the main advantage of using more selective pesticides is the preservation of beneficial insects in the orchard.
Insect pest control using broad-spectrum chemicals can create secondary pest problems. In almonds, he said green stink bugs and leaffooted bugs can present control problems. Visual monitoring for signs of adults and nymphs is important, he said, but not always possible when a PCA has multiple blocks to cover.
Lumbreras said he goes by the insect damage history of a block with plant bugs. Crop damage is not always visible until harvest.
“You can kill them with pyrethroid applications, but then you are chasing mites during the growing season,” Lumbreras said.
Keeping those mite predators alive is important, he said. The two main mite predators are six-spotted thrips and western predatory mites. Six-spotted thrips are highly mobile and an efficient mite predator, feeding on 50 mite eggs per day and capable of doubling their populations in four days.
“Selective materials to target plant bugs are a tool we need,” Lumbreras said.
He added that the more selective pesticides allow biological control of mites, and they also have a longer residual effect.
They are more expensive to apply, but he believes they are cost-effective, eliminating the need for multiple mite sprays.
For example, he noted that the cost for a pyrethroid is relatively cheap at about $6 per acre. The product he uses for plant bugs, Avaunt eVo, is in the upper $20s per acre to apply.
Biopesticides Offer Another Option
Biopesticides are another alternative control route. Most affect only the target pest and closely related organisms. The majority of biopesticides have a short residual. They can achieve around 50% control, Post said.
Biopesticide use has been increasing. They can be used as stand-alone treatments or combined or rotated with other pesticides in both organic and conventional production systems. The fact that there are no residues is a huge benefit for export crops.
University of California, Davis reports that biopesticides have long been used in combination with synthetic chemistries in pest control programs that can also manage resistance, as they typically have modes of action that are different from synthetic pesticides.
It should also be noted that “softer” pesticides can still affect pollinators and should not be used when bees are present. One exception would be Bacillus thuringiensis, which may be used at petal fall and after for control of peach twig borer.
Publisher’s Take
The Big Picture: What to do Next
1. Selective pesticides can preserve beneficial insects
Softer chemistries help maintain predator populations that naturally suppress mites and secondary pests.
2. Timing and coverage are critical
Selective products often target eggs, larvae or nymphs rather than adults, making scouting and spray timing essential for effective control.
3. Better spray coverage can improve returns
Research showed slower spray speeds and properly maintained nozzles improved upper-canopy coverage and pest control performance.
4. Resistance management still matters
Rotating chemistries and avoiding repeated use of the same products on successive pest generations can help slow resistance development.
5. Higher upfront costs may reduce season-long expenses
More selective materials may cost more per acre, but they can reduce flareups of mites and secondary pests, potentially lowering total treatment costs.
Cecilia Parsons | Associate Editor
Cecilia Parsons has lived in the Central Valley community of Ducor since 1976, covering agriculture for numerous agricultural publications over the years. She has found and nurtured many wonderful and helpful contacts in the ag community, including the UCCE advisors, allowing for news coverage that focuses on the basics of food production.
She is always on the search for new ag topics that can help growers and processors in the San Joaquin Valley improve their bottom line.
In her free time, Cecilia rides her horse, Holly in ranch versatility shows and raises registered Shetland sheep which she exhibits at county and state fairs during the summer.