Written by Louis Nottingham, WSU, May 2019
Greater densities of pear psylla adults have been observed this spring than in 2018. Many orchards in the Wenatchee River Valley have hundreds of eggs on nearly every fruiting bud. However, our recent dissections and tap counts suggest that these adults are running out of steam, at least in the lower valley (Columbia River to Monitor). Adults densities are declining and they are no longer laying eggs, meaning they are at the end of their lifecycle. First instar nymphs are just appearing in our plots at the TFREC and in Rock Island, so it may be a while before we see the bulk of summerform adults (3-4 weeks) (Figure 1).
Petal fall sprays should target 1st to 3rd instar nymphs. This is an important spray timing because young nymphs are probably the most susceptible psylla stage to insecticides, and thorough spray coverage is still achievable. However, this timeframe is key for natural enemy recruitment. Allowing natural enemy populations to build is critical for mid to late summer control, when the potential for good spray coverage decreases. To capitalize on psylla’s susceptibly at petal fall and conserve natural enemies, growers should implement soft spray programs.
Soft Spray Program Strategy
Soft spray programs following bloom should avoid tank mixes of multiple broad-spectrum insecticides and instead, spray multiple times on a shorter interval (2 to 4 sprays, 5 to 10 days apart) with softer materials alone or tank mixed with other soft materials. In other words, instead of one knock-out spray, chip away at the psylla population with suppressive sprays. This approach has a much lower impact on natural enemies. Soft materials that are effective on psylla nymphs include organic insecticides like azadirachtin (Neemix and Aza-Direct), diatomaceous earth (Celite 610), Cinnerate, or selective conventional materials such as Esteem, Dimilin, and Centaur. Our field trials have shown that repeated soft sprays can suppress heavy infestations of psylla while allowing natural enemies to persist (Figure 2). Remember, no matter how much you knock down the current psylla population, re-infestation by summerform adults is likely due to their high mobility. Therefore, it is not necessary to completely eliminate your psylla, especially at the cost of killing off natural enemies. Psylla will come back, so you are better off having some natural enemies in the orchard when they do.
Codling moth management affects psylla management.
Implementing a soft spray program for codling moth is important to protect natural enemies of psylla. Starting with mating disruption will greatly improve the efficacy of a soft codling moth program by reducing baseline moth pressure. Using the Decision Aid System (DAS) will help ensure accurate spray timing. Focus on using soft materials like oil, Cyd-X, Intrepid, Altacor, Esteem and Dimilin.
Use pesticides with care. Apply them only to plants, animals, or sites listed on the labels. When mixing and applying pesticides, follow all label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. If pesticides are spilled on skin or clothing, remove clothing and wash skin thoroughly. Store pesticides in their original containers and keep them out of the reach of children, pets, and livestock.
YOU ARE REQUIRED BY LAW TO FOLLOW THE LABEL. It is a legal document. Always read the label before using any pesticide. You, the grower, are responsible for safe pesticide use. Trade (brand) names are provided for your reference only. No discrimination is intended, and other pesticides with the same active ingredient may be suitable. No endorsement is implied.
Louis Nottingham, PhD
Postdoctoral Research Associate
Washington State University
Tree Fruit Research & Extension Center
1100 N Western Ave., Wenatchee, WA 98801
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