MITE VACCINATIONS FOR SUSTAINABLE MANAGEMENT OF SPIDER MITES IN VINEYARDS

Abstract

We have successfully released phytophagous Willamette mites into Zinfandel vineyards that have had chronic problems with the economically more damaging Pacific spider mites. These releases induced resistance in the grapevines, causing smaller populations of Pacific mites and higher berry sugar concentrations. This study addresses the sustainability of our techniques. We define a sustainable technique as one that (1) is effective, (2) requires low inputs of resources, (3) is self-perpetuating, (4) produces minimal pollution, (5) produces minimal effects on non-target organisms, and (6) is compatible with other agronomic practices. Most of these criteria are met by our inoculation techniques; here we seek to determine the persistence of Willamette mites from one season to the next, and to evaluate effects of several commonly used agronomic practices on our vaccinations. Our data suggest that Willamette mites can be introduced a single time into a vineyard; they will reduce populations of Pacific mites and persist from year to year in the absence of miticides or other disruptions. We observed Willamette mites overwintering commonly on the grapevines and on box elder (Acer negundo) foliage adjacent to vineyards. Pacific mites were not observed overwintering in vineyards, and we surmise that they generally blow into vineyards during each growing season. We did not observe Willamette mites overwintering on cover crops although other phytophagous mites and predatory mites were found. In preliminary observations, we found no strong effects (positive or negative) associated with cover-cropping in terms of mite management. Vineyards with Pacific mites are often treated with miticides, either dicofol or propargite. We found that dicofol (but not propargite) was extremely disruptive to mite populations; after an initial kill, applications of dicofol were consistently associated with resurgences of mites that exceeded numbers found in unsprayed controls. Unlike applications of miticides, introductions of Willamette mites to control Pacific mites satisfy our criteria for sustainable agriculture. Here we demonstrated that they are self-perpetuating at low numbers from one season to the next. Furthermore, releasing Willamette mites for control of Pacific mites is compatible with some, but not all, management practices.