SPIDER
MITES - not insects but Arachnids, a group which
also includes spiders and ticks. Spider mites are a
common problem. While there are several species, the
illustrated Two-spotted Spider Mite, Tetranychus
urticae, is one of the more common mites you are
likely to encounter, and it feeds on a wide range of
plants. Since these mites are extremely small, magnification
is necessary to get a good look at them. The two-spotted
spider mite is pale yellow or green often with two
brown spots; at times some spots may be an orange-reddish
color. These pests feed by piercing the undersurface
of the leaves with their mouthparts and sucking up
the plant juices. When leaf surfaces develop pale speckling,
a closer look may reveal patches of webbing underneath
the leaves, and with the aid of a magnifying lens you
will probably also notice many tiny round eggs. (See
the entry on thrips for an
image of these eggs.) Heavy damage causes leaves to
look dry and discolored, and since spider mites are
more of a problem in hot, dry conditions, this may
be wrongly attributed solely to the weather. Reproduction
is rapid resulting in many generations a year, and
the use of certain insecticides can actually increase
mite populations. They are also favored by high levels
of nitrogen fertilization. Many other insects and mites
feed on spider mites and their eggs, including some
thrips. Keep plants sufficiently watered to prevent
drought stress and frequently spray the leaves with
water, especially underneath, as forcefully as possible
without damaging the plants to remove and discourage
the mites. |
