Augmentative biological control of twospotted spider mite on hops in the Midwest

The twospotted spider mite, Tetranychus urticae is a key pest on hops, affecting the quality and quantity of yield. Hop production is a new industry in the midwestern USA, and little is known about mite management in this region. During 2016, a trial was conducted to determine the efficacy of augmentative biological control. Treatments of high and low rates of both Neoseiulus fallacis and Galendromus occidentalis were compared. T. urticae populations were monitored weekly at four Ohio hop yards. When populations reached a threshold of one T. urticae per ten leaves, predatory mites were purchased from a commercial insectary and released. Hop yields did not differ significantly among treatments. During 2017, a similar trial was conducted using more intense sampling, to ensure early detection of spider mites in a system where mite density varies widely within plants and between adjacent plants. Treatments compared N. fallacis released at both a high and low rate. The yield showed no significant treatment effect. Although yields in the field release trial did not show treatment differences, concurrent enclosure studies showed that N. fallacis does provide adequate control of spider mites when released at a rate of two predators per ten spider mites. Enclosure studies showed that the naturally occurring predator complex, which includes N. fallacis, provides substantial control of T. urticae. Future studies might concentrate on identifying tactics for conservation biological control where growers would enhance the activities of natural enemies already present in the system, rather than releasing purchased predators