|Hop yard in western NC, July 2010 Hop Tour. Photo: HJB|
|Hops leaves respond to relatively low mite densities. The yellow stippled area on this leaf had a population of spider mites feeding on the opposite side. Photo: HJB|
The only way to know if your mites from last year have stuck around is to look for them. Sample 10 leaves per variety weekly and observe with a minimum 10x hand lens. It will take some practice, but you can see and count mites with a hand lens. You can distinguish predatory mites from pest mites by size (they are smaller), shape (most are tear drop shaped or oval), and color (P. persilimis) is orange. Predatory mites also move much faster than pest mites. See here for images of some of the predatory mites commonly used for biological control. Start sampling when you have new leaves and continue weekly. When and if you release additional predatory mites will depend on when spider mite pests appear in your planting."