Leafrollers are nearly impossible to sample when they are in the first 2-3 instars because they are so small. DAS provides intervals during which sampling should occur well ahead of time.
To sample leafrollers, take 25 shoots from 1 tree per 1.5 acres and count the number of larvae (caterpillars). In trees over 10 feet (3 meters) tall, more Pandemis leafroller larvae are in the upper half of the canopy. Sample from that part of the tree to avoid underestimating the density.
While sampling at the DAS recommended time periods is relatively easy (because the larvae are larger), it occurs after control sprays have been applied. However, it is a good indication of larval density, if previous control tactics were effective, and allows you to determine if treatment of the second generation is necessary.
If more than 2% of shoots have live larvae immediate re-treatment should be considered or a summer treatment should be applied at the proper timing based on the model. If you used Esteem, leafroller larvae will remain alive until they molt to the pupal stage, therefore post-treatment samples should not be used to assess the need for retreatment. In most cases where Esteem is used leafroller populations do not reappear in summer, however, sampling at the appropriate time in summer should be conducted to verify the efficacy of the Esteem treatment.
(Jay Brunner & Vince Jones, WSU TFREC)
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