by Philip McIntosh
SPIDER MITES
Of all garden pests, the TWOSPOTTED SPIDER MITE may be the most feared.
These little critters are hard to get rid of and can wreak havoc on your crop.
THE TWOSPOTTED spider mite (Tetranychus urticae) is quite
possibly the most hated—and
feared—of all plant pests. RELATED TO their fellow
arachnids, the spiders (no surprise),
there are more than 1,200 species of
mites and they all look pretty similar. BESIDES THE red predatory
mite, there are other predatory mites
as well as midges and beetles available
as biological control agents.
ALTHOUGH THE creatures SPIDER MITES must be SPIDER MITES like to hang out
SPIDER MITES are a DO NOT mistake the red
THE WEBS of spider mites are SPIDER MITE infestations can
themselves are small (0.4-0.5 mm,
about 1/50 of an inch) and difficult
to see, their distinctive webs and
sometimes swarming behavior
can give them away. A hand lens
is recommended when inspecting
plants for their presence before
they get too abundant.
studied closely to be sure of the
exact species identification. The
twospotted spider mite is generally
pale but variable in color with two
dark spots on the dorsal side.
challenge to treat with pesticides
because of their tendency to be
on the underside of leaves and
the rapid onset of resistance.
Insecticides are generally
ineffective and miticides may
require multiple applications
before control is achieved.
much finer than most spider webs
and in severe infestations,
mites can be seen moving
about en masse over
the webs.
on the undersides of leaves where
they use their piercing mouth parts
to suck the sap out of plants. This
damages chlorophyll, causing pale
speckling of the leaves.
predatory mite (Phytoseiulus
persimilis) for the twospotted spider
mite. Red predatory mites are
beneficial, able to eat several adults
and many spider mite eggs in a day.
Red predatory mites are more solitary
than the twospotted variety and seem
to move about frantically on surfaces.
arise quickly at low relative humidity
(20-40 per cent) when temperatures
are above 85°F. Overhead watering
helps keep humidity up and can
wash mites off of leaves.
groundbreakers
137