The main wasp species, however, don't complete development on apple aphid, so the biological control they provide is limited. It controls aphids quickly, and is less toxic to most predators than the organophosphate and carbamate insecticides available. Some consultants try not to completely eliminate the aphids, adjusting rates to leave a small residual population for aphid predators to feed upon. This trend also been found in the mating disruption blocks that Dr. Beers is monitoring for secondary pests across Washington, in comparison with conventionally managed blocks. A consistent relationship exists between tree vigor and aphid populations.
Aphids reach higher levels in blocks where terminal growth continues well into the summer.
One consultant noted that aphids increase with the application of foliar urea sprays, as is done in some Granny Smith blocks. Conversely, another consultant found that aphids were generally lower year after year in blocks in which the grower had reduced nitrogen levels to improve fruit color on Red and Golden Delicious. S everal tours are planned for this summer featuring developments in tree fruit pest management, including information on new insecticides, mating disruption and other new pest control technologies. Time and meeting location to follow in next newsletter. Dr. Max Suckling with New Zealand HortScience and Dr. Gerhard Karg with the University of Kaiserlautern in Germany have published research on the distribution of pheromone in treated orchards and vineyards, the role of the absorption of pheromone by leaves, and the relationships of pheromone point sources, atmospheric pheromone concentration and moth behavior.