Quick Facts...
- Several species of spider mites can damage turfgrass in Colorado: clover mite, Banks grass mite and brown wheat mite.
- Most damage occurs during early to midspring.
- Damage to turfgrass is primarily related to dry conditions and turfgrass stressed by drought.
- Clover mites can be a serious nuisance pest when
they enter buildings in spring.
Many species of mites are common in Colorado turfgrass. Some, such as the oribatid or "hardshell" mites, are important in the breakdown of thatch and the recycling of nutrients. Other are important predators of pest insects and mites. Three spider mites species are among those that damage Colorado turf: clover mites, Banks grass mites and brown wheat mites.
Clover Mites
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| Figure 1. Clover mite with egg. |
Clover mites (Bryobia praetiosa) are a common type of spider mite in Colorado. They breed outdoors on turfgrass, clover and other plants during spring and fall. During October and November, clover mites seek protected areas to overwinter and may move into homes in large numbers. This also occurs from late February through early May. They are a common indoor nuisance problem at either time.
Clover mites are smaller than the head of a pin and range in color from reddish or brown to dark green. Under close examination they have an unusually long pair of front legs, which distinguishes them from the common spider mites found on garden plants.
Clover mites are most often encountered as nuisance pests in homes. During warm days in fall and spring, large numbers of clover mites may become active and enter homes through cracks around windows and doors. South-facing walls usually are more heavily infested. The crawling mites may spread to walls, curtains, furniture and carpet. Typically, clover mites are described as "walking dust specks." Although they do not bite people, transmit diseases or feed on household furnishings, they can be a serious nuisance. When crushed, clover mites leave rusty red stains that are noticeable on white surfaces.
During early to midspring, clover mites also may damage turfgrass around building foundations and in other warm, dry areas of a lawn. Feeding damage appears as small, meandering silver streaks in the leaves. When mite populations are high, leaves may be extensively injured and die. Areas of grass extending several feet from the building foundation may be totally killed, appearing as light brown, irregular dead patches.
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| Figure 2. Clover mites on sticky card. |
Clover mite injury to turf is commonly mistaken for winter kill and usually
is found in the same sunny, dry areas of the lawn where winter drying
problems occur. Furthermore, almost all injury occurs within 10 feet of
a building, tree or some other upright surface. This is because clover
mites periodically climb out of a lawn to shed their old skins and lay
eggs.
Clover mites produce two or more outdoor generations during the cooler seasons, feeding on grasses and other plants. However, turfgrass injury occurs only early in the growing season, from February to May. As temperatures warm in late spring, clover mites produce dormant eggs that do not hatch until the return of freezing temperatures in fall. Because of this habit, clover mites are considered cool-season mites, in contrast to many other spider mites that cause greatest damage during warm months.
Control
Migrations of clover mites into buildings can be largely deterred by
keeping grass and other host plants away from the base of the foundations.
Usually a plant-free barrier of about three feet will be sufficient, although
sometimes this may also be crossed. Since clover mites almost always enter
the sun-exposed sides of buildings (i.e., south, west) this barrier is
best established in these areas.
Carefully sealing/caulking all exterior openings through which mites
enter can also prevent indoor migrations. Give particular attention to
cracks around windows. Clover mites migrations can also be prevented by
use of a fine layer of various dusts around windows and other points of
entry. Talc-containing baby powder, diatomaceous earth, and even baking
soda or corn starch may create an effective barrier through which clover
mites can not pass. Clover mites should not be crushed, as they will leave
a rusty stain, but can be vacuumed. Left alone, clover mite problems end
on their own with warm weather in May or early June, forcing them into
summer dormancy.
Clover mite populations on lawns can be greatly reduced by providing
some supplemental watering to areas where clover mites develop, such as
warm, dry areas at the base of sun-exposed walls and around evergreens.
This can be supplemented with spot spray treatments of insecticides in
those areas where clover mites develop. However, presently there are no
highly effective chemical controls for clover mites. Insecticide formulations
labeled for use on lawns and that have either the active ingredient bifenthrin
or lambda-cyhalothrin are most likely to assist in control of clover mites.
Banks Grass Mite
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Figure 3. Banks grass mite.
(Photo by F. Peairs.)
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Figure 4. Banks grass mite turn injury.
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Banks grass mite (Oligonychus pratensis) is a common mite species
in Colorado. It is a serious pest of corn and also damages drought-stressed
turf. It causes grass to turn a bleached straw color, often killing it
rapidly. The Banks grass mite adapts more to warm weather than the other
common turf damaging mites and is found throughout most of the growing
season.
Banks grass mite differs considerably in appearance from the other turf-damaging
mites. It is smaller and lighter in color. During most of the season,
it is green; the young stages are a paler color. During periods when the
mites run out of food or environmental conditions are unfavorable, they
may temporarily turn bright red. This mite lacks the elongated front pair
of legs of the clover mite. It is related to the spruce spider mite (Oligonychus
ununguis), a common pest of evergreens but with different feeding
habits.
Banks grass mite is more destructive to turf than other turfgrass mites. In
early stages of feeding injury, there is small, white flecking (stippling)
similar to that of other mites. A slight purpling of the injured grass
blade may be observed, which also is associated with brown wheat mite
injury. Dead grass takes on a brownish-yellow color and the blades are
stiff. Under favorable conditions, severe injury can progress rapidly.
Almost all serious injury by Banks grass mite is related to drought stress.
Banks grass mites spend much of the time feeding and resting at the base of the grass plant. This makes them somewhat difficult to detect and inhibits effective control.
Control
Banks grass mite is a difficult species to control with pesticides. Probably
most effective are turfgrass products that contain either lambdacyhalothrin
or bifenthrin as the active ingredient. These are sold under several trade
names.
Base all control programs on adequate water to the site. This includes fall and winter watering as needed, since populations of the mites can build up during this period. Under conditions of drought, control of the mite is often unsatisfactory.
Brown-Wheat Mite
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| Figure 5. Brown wheat mite. (Photo by F. Peairs.) |
The brown wheat mite (Petrobia latens) occasionally damages
turfgrass during spring, similar to the clover mite. Problems generally
are associated with areas of drought stress and excessive winter drying.
However, unlike the clover mite, populations are not so concentrated around
buildings or trees. South-facing hills and highway medians are typical
areas where turf damage by brown wheat mite can be expected.
Control
Adequate winter and spring watering are important in limiting infestations
of brown wheat mite. If conditions promote turfgrass growth, the plants
usually outgrow injury. Brown-wheat mite appears to be susceptible to
insecticides used for control of other turfgrass mites.
For more information, see the following Planttalk
ColoradoTM script(s).
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