To make that happen, Brian Croft has a plan. Croft, a professor in Oregon State University's Department of Entomology working with OSU's Agricultural Experiment Station, has studied mites for more than 15 years. So growers have to minimize the pesticides that might kill the good mites. They probably also need an extra supply of good mites so they have the numbers to zap all the bad mites. So far, the plan is working best in mint.
Predator mites multiply like crazy in top-irrigated mint.
In the greenhouses of A.M. Todd Co., a mint handler near Jefferson, Ore., researchers have been multiplying mites on lima bean plants since spring. Starting in late August, they began turning loose more than 10 million predators in mint fields around the wetter areas of Jefferson, Eugene and Junction City, and in the drier areas of the Pacific Northwest, such as central and north-central Oregon, the Columbia River Basin and the East Yakima Valley of Washington and Idaho. Predator mites are good at over-wintering, so we should have enough in fields when spring rolls around if they disperse adequately. Next April, mint growers should check their fields. If they average more than one spider mite per plant and if the ratio of spider mites to predator mites is too high, they will have to spray with pesticides or bring in predator mites or both.