One of the keys to integrated mite control was that the western predatory mite Typhlodromus occidentalis could effectively control spider mites under certain conditions. In the picture, a “typh” attacks the larger European red mite.
PHOTO COURTESY OF ELIZABETH BEERS, WSU
By the late 1950s, mite outbreaks had reached a crisis stage in Washington’s apple orchards. New miticides were introduced regularly, but mites (the most important of which at that time was McDaniel mite) became resistant, sometimes within a few years. Despite four to six miticide applications, damage still occurred.
Dr. Stan Hoyt, entomologist with Washington State University in Wenatchee, began working on this problem, and discovered that the western predatory mite, Typhlodromus occidentalis (also known as Galendromus occidentalis), could effectively control spider mites under certain conditions.
The most important aspect was to minimize the use of pesticides toxic to the predator. These included high doses of organophosphates, such as azinphos-methyl (low doses were selective because the predator had become resistant); carbamates such as carbaryl; sulfur fungicides (especially after bloom), and nonselective miticides.
The second key was minimizing the use of pesticides toxic to the alternate prey, apple rust mite, which included many of the same chemicals (nonselective miticides, sulfur fungicides, carbaryl, and endosulfan).
The alternative food source allows predatory mites to survive during periods of low pest-mite densities.
The same principles of integrated control were implemented in other apple growing regions throughout the United States and Canada, but never with quite the same degree of success as the arid growing regions. The comparatively low incidence of disease problems, and hence lower fungicide use, greatly helped implementation of integrated control in the West. Apple maggot and plum curculio were not present, and the overall pest complex required a less intense spray program. In addition, the western predatory mite is a one of the more efficient mite predators, and is well adapted to dry conditions. Other phytoseiids do not have the same high reproductive rate; and other predators, such as the Stethorus beetles, are usually not attracted to mite populations until after high populations have already developed.