Predator mites (Phytoseiidae) play an
extremely important role in the management of spruce
spider mite because they feed mainly on eggs and
smaller mites. These mites are highly effective egg
predators and in fact outbreaks
of the spruce spider mite often follow
applications of pesticides that disrupt the
predator mite population.
Overhead watering combined with low
toxicity insecticidal soap alone are very effective
treatments for spruce spider mites during the
growing season (see Using
Insecticidal Soap To Control Spider Mites).
Applications of Insecticidal
Soap won't disrupt predator mites. During
late winter mite eggs that are found on needles and
stems can be controlled with horticultural oils.
Certain synthetic pesticides like carbaryl
(Sevin) are known to be particularly harmful to
predator mite populations and use of these materials
can often guarantee
a spider mite outbreak because they destroy
the predator mite populations! Therefore use
pesticides carefully and always monitor for
spider mite buildup following applications
especially in susceptible plants.
Spider Mite Guide
Tree Pests (Oregon, 2005)