Success of mite-fighting tactics evaluated: In Central Valley, early-season release of Willamette mites confers resistance on wine grapes

Wine grapes in the Central Valley serve as hosts for several species of mites. Because these species have radically different economic effects, their correct identification is essential. Field trials revealed that some management practices were far more successful than others. For instance, treatments with dicofol (a miticide) and car-baryl (for leafhoppers) produced resurgences of mite populations to damaging levels. Releases of predaceous mites provided inconsistent control of herbivorous mites, and cover crops did not provide any clear advantages for mite management, although they may have other benefits. However, releases of Willamette mites at low densities early in the growing season consistently reduced chronically high populations of Pacific mites throughout the season. (Willamette mites, though they can become pests, are not damaging at low densities.) Scientists do not fully understand how Willamette mite releases confer plant protection, but evidence suggests they stimulate the host plant to reduce fecundity and survival of Pacific mites. Manipulations of host plant resistance offer new possibilities for control of pests such as spider mites