Fruit Crops News
Biological Control of Mites in Midwest Apple Orchards
Part 1: Introduction
One of the most effective uses of biological control in Midwest fruit crops involves the
management of pest mites in apple orchards. There are three common plant feeding mites in
orchards: European red mite, twospotted spider mite, and apple rust mite. Of these, the first two
are of primary importance and the third rarely causes injury. The two spider mite species feed by
removing contents from the cells of the leaf; prolonged feeding by high populations can turn the
leaves a bronze color and interfere with normal leaf activity, stressing the tree and reducing fruit
size and quality. Because mites reproduce rapidly and have several generations per year, they
can build up to large numbers, especially during warm dry periods in summer. Orchard spider
mites have developed resistance to several common insecticides and miticides. Some of the
pesticides which are commonly used for mite control interfere with IPM programs by killing
beneficial predatory and parasitic insects. Therefore, there are several reasons for using
biological control to manage mites.
A large complex of predatory mites and insects feed on spider mites. Spider mites are rarely a
problem on unsprayed apple trees where the beneficials are not eliminated by broad spectrum
pesticides. This summer, we held our Wisconsin Apple Grower's Field Day at a large certified
organic orchard in western Wisconsin. Mites have never been a problem in this orchard because
of the very reduced pesticide program. Other orchards in the vicinity that use more traditional
pest control practices tend to frequently have spider mite problems often requiring two, three, or
more special miticide applications per year. Therefore, mites are often considered as "upset"
pests caused by other pest management practices that have resulted in the development of
pesticide resistance and the elimination of beneficials.
In Part 2 of this series, I will discuss the complex of beneficial predators that are important in
biological control of orchard mites; in Part 3, I will discuss the impact of pesticides on this
complex, and in Part 4, I will provide some specific guidelines for using beneficials as the basis
of an Integrated Mite Management Program.
- Dan Mahr, University of Wisconsin - Madison
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