Michigan State University Extension
Ornamental Plants plus Version 3.0 - 00001730
11/12/99

Spider mites


Spider mites are about the size of the smallest object you
can see with your eyes (0.1 to 0.5 mm). Despite their
small size, these mites can cause significant plant
injury. Spider mite damage usually appears as a light
speckling on leaves (Vis. 1), followed by a general bronze
discoloration. Heavy infestations can bronze an entire
tree. The easiest way to diagnose spider mites is to tap
an infested branch over a white piece of paper. Dislodged
mites will appear as tiny specks moving on the paper.

Spider mite populations develop rapidly under hot, dry
conditions, and plants under stress are particularly
susceptible to injury. Spider mite problems can also be
induced through the use of certain insecticides, such as
Sevin, which destroy natural enemies of the spider mites.

Properly watering and fertilizing plants is a primary
means of limiting spider mite injury. Forceful hosing of
the plant foliage can be particularly useful because it
can crush and dislodge many of the mites.

When heavy mite populations occur, it may be difficult to
get control with any pesticide.

Soap sprays can be used to suppress mites on plants that
are not injured by the soaps. Spray a small part of the
plant, then check it in four to five days to test plant
sensitivity to soaps. Such a treatment is best applied in
early summer before mite populations get too large.


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