Spider Mites Reference Page
Top: Crops: Dry Beans: Spider Mites:
Spider Mite in Dry Beans
Reference Page
Tetranychus spp.Tetranychus
spp.
Including Twospotted spider
mite Tetranychus urticae ID photos: 
fact
page (pdf): 
Strawberry spider mite Tetranychus turkestani
Pacific spider mite Tetranychus pacificus
fact
page (pdf): Strawberry spider mite Tetranychus turkestani
Pacific spider mite Tetranychus pacificus
Pest description and
crop damage
Several species of spider mites are common in the Pacific
Northwest.
Frequently, infestations include a mixture of spider mite species.
Adult mites are about
1/16
inch in length, have 4 pairs of legs, are greenish to pink or cream
colored, and
have various sized black spots on the body. Under warm conditions,
spider mites
move rapidly within the colony area.
Damaged leaves become
somewhat
stippled on the upper surface and may turn brown or bronze with heavy
damage.
The undersurface of leaves may have a grayish cast due to webbing.
Wilting, leaf
deformity, tissue death, and abscission all may take place. (Trivia
fact:
Twospotted spider mites can feed on 18 to 22 plant cells per
minute.
)
Biology and life history Spider mites have four stages of development: the oval, somewhat translucent egg; a 6-legged translucent larval stage; an 8-legged nymph stage; and the 8-legged adult stage. A resting or quiescent stage occurs at the end of the larval and nymph stages. A generation may pass in as few as 5 to 7 days in mid-summer, or in a month during cool periods. There are numerous overlapping generations each year.
Scouting and thresholds There is no precise survey technique for evaluating spider mite infestations. Infestations usually begin on the lower portions of the plants and move upward as mite numbers increase. Evaluating spider mite infestations is most efficient if randomly selected, older, lower leaves are picked and inspected for stippling on the upper surface and webbing, mites, and feeding scars on the lower surface.
Management—biological control
Spider mite populations may
be held
at very low levels by a number of insect and mite predators,
particularly early
in the season. Thrips are effective early season predators, feeding
primarily on
spider mite eggs.
Commercial releases of
predatory
mites are used to control spider mites in greenhouses. In Florida,
predatory
mites were used to control spider mites in strawberries. Spider mites
provide an
important food source for predators such as minute pirate and bigeyed
bugs.
Management—cultural control
Spider mite problems can be
reduced
by keeping fields and field margins clean of weed hosts. Spider mite
populations
may increase more rapidly in areas where dust deposits are heavy.
Reducing dust
may reduce the spider mite problem. Spider mites are usually less
severe in
sprinkler-irrigated fields than in furrow-irrigated fields. Excessive
nitrogen
fertilization also may contribute to population buildup. Minimizing
early season
insecticide applications, which reduce populations of beneficial
insects, will
reduce spider mite outbreaks.
Management—chemical control
1. aldicarb (Temik 15G) at
1 to 2 lb
ai/a. PHI 90 days. Use at planting. ID and WA 24c. Postemergence
side-dress.
2. insecticidal soap
(M-Pede) at 1
to 2% (see label for gal/a). Potassium salts of fatty acids. PHI zero
days.
3. dicofol (Kelthane) MF at
0.5 lb
ai/a. PHI 7 days. Do not feed.
4. dimethoate at 0.5 lb
ai/a. PHI
zero days. Do not feed treated vines.
5. disulfoton (Di-Syston)
at 1 to 2
lb ai/a. PHI 60 days. Use at planting or sidedress. Do not apply more
than once
per season. See label for rotational crop restrictions. WA and OR
only.
6. naled (Dibrom 8E) at 1
lb ai/a.
PHI 1 day. Do not feed treated vines.
7. phorate at 0.9 to 1.4 oz
ai/1,000
row ft. PHI 60 days. Use at planting only.
8. propargite (Comite) at 1.6 to
2.4
lb ai/a. PHI 14 days. Do not feed any parts of treated plants to
livestock. Do
not use more than twice per season.Source: 2004 PNW Insect Management Handbook
August 6, 2004-jn