Biological Control of Two-spotted Spider Mite on Vegetables

Two-spotted spider mite (TSSM) is a serious pest of solanaceous and cucurbit crops throughout much of the Southern U.S. Management has been achieved almost exclusively with chemical acaricides, usually multiple applications per season, which has led to costly control measures and the development of acaricide-resistant populations. Naturally occurring populations of P. persimilis in Rowan County have been observed controlling TSSM on tomatoes in late August and September, provided growers recognize them as beneficials and avoid spraying harmful insecticides. Unfortunately, there is a considerable lag time between the buildup of TSSM and predators in tomato fields early in the season (July to mid-August), which is when mite populations and acaricide use are most intense. This project investigated early season release strategies of both tomato-adapted and bean-adapted P. persimilis, and showed that releases of predators at 21,000 per acre when TSSM populations are still low (about 0.5 mites per acre) led to TSSM population reductions within three to four weeks after release. However, success is highly dependent on avoiding insecticide applications toxic to P. persimilis, most importantly pyrethroids. Insecticide compatibility studies showed that drip chemigation of insecticides or a foliar program of predator-safe pesticides both conserved predator populations and resulted in net profits similar to that of a broad spectrum insecticide program. More than 300 growers and 45 extension agents were targeted in educational programs that included on-farm demonstrations/tests, presentations at commodity meetings, field day presentations, a two-day extension agent training program, and development of a vegetable crop biological control website focusing on P. persimilis and TSSM. Future programs should focus on developing more strategic predator release strategies to improve the economics of P. persimilis releases, and improved understanding of the overwintering ecology of endemic P. persimilis necessary to develop habitat manipulation practices to promote early season inoculation of fields.

1. Determine the distribution of resident populations of persimilis in different ecoregions of NC (mountains, piedmont and coastal plains), and overwintering sites in regions where they do successfully overwinter.
2. Compare efficacy of different commercial sources and release rates of persimilis in controlling TSSM on tomatoes.
3. Determine the level of TSSM suppression in tomatoes using a within field tomato-based banker plant system and a periphery bean-based banker plant system for releasing persimilis into commercial tomato fields.
4. Compare different insecticide-based management programs for compatibility with persimilis, efficacy in managing key insect pests, and net profitability of tomato production.