Nymphs resemble full-size adults, but may have 6 or 8 legs, depending on stage, but do not have the ability to reproduce.
Adults are very small at only 1/60 (female) to 1/80 (male) inch in size - approximately the size of salt grains - when fully developed. Adults are greenish yellow to orange to brown with 2 darker spots - similar to saddle bags - on their body.
Symptoms
Leaf shows spider mite stippling.
Two-spotted spider mites damage crops by piercing leaves and feeding on the plant juices. Mites suck on the bottom sides of soybean leaves, removing plant moisture and nutrients, resulting in a yellow or whitish spotting on the top side of the leaf surface. In heavy infestations, it's common to see leaf burning and stippling.
Hot spots will typically be noticed first on field margins, as infested plants take on a wilted appearance. Drought-prone fields or field areas that contain lighter soils or sands are often affected first by spider mites. As populations increase, two-spotted spider mites will move across the entire field if left unchecked.
Spider mite feeding in a soybean field.
Life Cycle
Two-spotted spider mites have 4 stages of development: egg, larva, nymph and adult.
This pest overwinters as adults in field edges and roadsides bordering fields, feeding on weeds until spring.
After early spring mating, female spider mites lay eggs on weeds that usually hatch in 3 to 5 days.
Two-spotted spider mites do little feeding during the first larval stage of development.
Females live 20 to 30 days and typically produce 50 to 100 eggs during their lifetime.
The entire life cycle of this pest can be completed in 5 to 14 days. This pest has the potential for up to 10 generations per year during the growing season.
Populations of spider mites increase significantly during extended hot, dry conditions.
Management
Two-spotted spider mites are difficult to see with the naked eye so conduct a simple "paper test" by shaking the plant over a white paper plate. This will allow a grower to see the tiny orange- to yellow-colored mites slowly moving on the paper.
Some universities suggest treating for this pest if 20-50% of the leaves are discolored before pod set. After pod set has begun, the suggested treatment threshold is 10-15% of the leaves discolored.
Natural predators, including fungi and thrips, can help keep populations in check.
If a spray treatment is made, the most consistent performance has been with a full rate of an organophosphate.
Natural predator populations can be affected by spray applications of synthetic pyrethroids.
Residual control of most treatments is short-lived and applications only control adults and nymphs. Scout fields 5 to10 days after spray applications to check for re-infestation.
