Integrated Mite Management
Few success stories in the history of tree fruit
Integrated Pest Management have been more dramatic and had more
that of integrated mite control in apple orchards.
In the early 1960s a crisis of mite control resulted in trees with
brown leaves in late summer, even though several chemicals had
been applied to control spider mites. The implementation of integrated
mite control in the late 1960s reduced the need for applying chemical
controls for spider mites. For the last 30 years only about 10
percent of Washington apple orchards have been treated annually
with pesticides specifically for control of spider mite.
components have led to this widespread biological control:
- Use of a delayed dormant oil against overwintering European
red mite eggs.
- Maintenance of a moderate apple rust mite population in the
orchard as an alternate
food supply for predatory mites.
- Use of selective pesticides to conserve predators in the orchard.
Tetranychidae - Spider mites
The twospotted spider mite
is an economic pest of
Overall, the spider mites are one of the largest,
most important and most destructive groups of pests in agriculture.
Spider mites have several natural enemies. However, some broad-spectrum
pesticides used for insect control can reduce or eliminate them
from orchards. For that matter, many miticides (chemicals that
specifically kill spider mites) are as toxic or more toxic to predatory
mites than to spider mites.
Release from biological control (through
use of pesticides)
allows European red mite
Apple growers can effectively adopt practices
that will allow predatory mites to survive in their orchards. While
such practices might not immediately solve spider mite problems,
it can lead to more stable, long-term mite control and have the
added benefit of eliminating or slowing the development of spider
mite populations that are resistant to miticides.
Eriophydae - Rust Mites
Rust mites can be an alternative
food source during periods of low spider mite densities.
Rust mites play a critical role in integrated mite control because
they are an alternate food source for predatory mites. The presence
of apple rust mites in orchards allows predatory mites to survive,
especially when spider mite densities are low. If predatory mite
densities are too low, spider mite densities can rapidly increase
and cause damage to apple trees before predatory mite densities
can increase to levels providing control. When predatory mites
can find apple rust mites they maintain higher densities in apple
trees and are then able to attack spider mites before their densities
reach damaging levels.
Phytoseiidae - Predator Mites
The Western predatory
mite feeds on spider mites that
The predatory mites are the most important biological control
agents in the Pacific Northwest. The western predatory mite,
Galandromus occidentalis, is by far the most important predator
in most orchards.
Three factors limit the number of western predatory
mites in an orchard:
Number of prey
Since apple rust mites usually become numerous during May and
June, numbers of predatory mites can increase rapidly during
that period as they feed on the rust mites, reproduce and disperse
over the tree. Predatory mites usually do not completely eliminate
rust mites but keep their numbers below levels that cause leaf
damage. Because of their importance in sustaining predatory
mites in orchards it is critical to follow practices that keep
apple rust mites in orchards.
Cold, dry winter weather can drastically reduce the numbers
of overwintering predatory mites. However, if there are
sufficient numbers of rust mites as food in
spring, predatory mite populations can rebound in time to control spider
Applications of pesticides that are highly toxic to apple rust
mites or predatory mites have the most devastating effect
on biological control of spider mites.
Because spider mites are usually not affected by pesticides toxic to predatory
mites, their densities can develop during the time it takes for
predatory mite populations to recover from the pesticide
This information was derived from Orchard
Pest Management -
A Resource Book for the Pacific Northwest. Edited by:
Elizabeth H. Beers, Jay F. Brunner, Michael J. Willett and Geraldine
Published by Good Fruit Grower, Yakima, WA, 1993.