Clover Mite

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Clover mite adults and feeding spots on grass blade.
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Clover mite adults, nymphs and eggs on side of irrigation switch box.
  • Scientific Name: Bryobia praetiosa Koch has several recognized biotypes, some of which seem to prefer feeding on grasses and others on various trees. [Phylum Arthropoda: Class Arachnida: Order Acari: Family Tetranichidae]


  • Common Names: clover mite


  • Climatic Zone: temperate


  • Geographic Distribution: The clover mite is a cosmopolitan species found in North and South America, Europe, Asia, Africa and Australia.


  • Damaging Stage: larvae, nymphs and adults


  • Hosts: Though originally described from red clover, clover mites attack a wide variety of plants including several turfgrasses such as Kentucky bluegrass, perennial ryegrass and fescues.


  • Damage Symptoms: Like other mites, the clover mites probe the surface cells of grass blades, extracting their contents which produces a silvery appearance to the upper surface. This “frosting” of turf is most common around protected places next to buildings or under trees. On golf courses, this damage is similar to and may be misdiagnosed as winter desiccation caused by wind.

The major problem with these mites is their nuisance activities. They tend to migrate into homes and buildings during population flushes in the spring and fall. Though they do not transmit any disease nor do they bite, they are quite annoying to the average homeowner. When crushed, they leave a red stain which is difficult to remove. On golf courses, this mite occasionally invades shelters and stains the light colored clothing of players unfortunate enough to sit on them. The mites also may cluster on sprinkler system switch boxes where they coat the surface with cast skins and egg shells.


  • Description of Stages: Clover mites have life stages typical of mites (i.e., egg, larva, nymphs and adult).


Eggs: The small round eggs are shiny red orange colored and about 1/64 inch (0.12 mm) in diameter.

Larvae: The larvae have only three pairs of legs and are reddish in color.

Nymphs: The nymphs take on another pair of legs and have the typical adult form of a slightly depressed, oval body with elongate front legs. Under high magnification, the body is covered with tiny fingerprint like ridges. There are two nymphal instars.

Adults: Only females are known and these are reddish to chestnut brown in color. They have the front legs about twice the length of the other legs and are about 1/32 inch (0.4 mm) long.


  • Life Cycle and Habits: The clover mite is a true "cool season" mite. In the cool season areas, this pest overwinters as bright red-orange eggs attached to walls of buildings, tree trunks, but adults sometimes survive in basements and other protected areas. Clover mites also oversummer in the egg stage, being active during the cool of the spring and fall. In the southern zones, this pest oversummers in the egg stage but adults and nymphs may be active during the entire winter.

Generally, when spring temperatures get above freezing, the eggs hatch or in milder climates, the adults become active and begin to lay eggs. Spring deposited eggs hatch in a week at 28 to 48 °F while overwintered eggs will hatch in 12 to 18 hours. The larvae feed for several days before they seek out a protected site to remain dormant for a few days while the molting process is completed. This behavior continues for the two nymphal instars - feeding, seeking out a protected site, remaining dormant, molting, and returning to feed. From this behavior, structures (building siding, signs, irrigation boxes, etc.) often become coated with a white powdery material which is actually the cast skins and eggs shells of this mite. Overwintering adults continue to lay eggs until mid April while new spring adults lay eggs which do not hatch until the following fall. The spring generation takes about a month to mature and is active from snow melt to mid June. Oversummered eggs hatch in September and the mites mature in 25 to 35 days. These adults lay additional eggs which hatch in the fall or delay hatching until the following spring. There are usually two to three generations in the fall and two to three in the spring. The mites are strongly attracted to warm surfaces during cool weather and will climb up the sides of buildings and trees. On buildings, they may enter doors or windows and become a nuisance inside.


  • Control Approaches: This is an occasional pest which produces nuisance populations during favorable years when long, moderately cool spring or fall weather helps build up populations. Generally little turf damage occurs but invasions into buildings and homes may become unacceptable.

Cultural Control - Establish Barriers and Exclusion - Removing turf from directly touching the foundation of a home or building and replacing it with a barrier of ground cloth covered with mulch or gravel can often stop clover mite invasions. Also check all lower windows, doors and their frames for seals and caulking. If these structures are not well sealed and caulked, the mites can easily creep into the structure.

Chemical Control - Barrier Treatments - Since the mites often enter houses and buildings from populations that are active in surrounding turfgrass, treat the parameter turf (usually a three to ten foot wide strip is suitable) with an appropriate miticide/insecticide.

Chemical Control - General Turf Sprays - Monitor mite populations during the spring or fall, especially when cool temperatures have lingered. If the mite populations are increasing and the site has a history of clover mite problems, general cover sprays of a miticide will reduce the population and prevent invasion. Use selective miticides/insecticides and avoid late spring treatments since the mites will have laid summer eggs which are not susceptible to the treatments.


Monitoring

Clover mites are best detected as the sun begins to set in September to November and again in February into early June. They are also active on cool, overcast days. An insect sweep net can be used to scoop up the mites for an hour after the sun sets or they can be simply observed by getting down our your hands-and-knees. The mites will often stain the hands and knees reddish-orange with some olive-green streaks. If the turf appears silvery as if from winter desiccation or the mites are invading public areas, control measures are warranted.