Adult strawberry rootworms are brown to black, shiny, oval-shaped beetles
with four blotches on the shell-like wing covers. Adult beetles overwinter
in mulch and soil crevices and become active in May and June. They eat
small holes in leaves, and females lay eggs on older leaves near the soil
surface. Larvae burrow into the ground to feed on strawberry roots during
the summer. New adults begin emerging in mid-summer, and these beetles
feed on strawberry foliage through early fall.
rootworm, adult and larva. Adults is about 1/8 inch (3 mm) long.
Larvae is slightly longer.
Although the larvae of the strawberry rootworm, Paria fragariae,
feed on the roots of strawberry (as the insect's common name implies),
leaf-feeding by adult beetles is more damaging to strawberry production.
When adults become numerous during mid-summer, strawberries may be riddled
Adults feed primarily at night, and scouting for their presence is best
done by using a flashlight to examine plants after dark. Populations of
10 to 20 beetles per square foot are considered high. Although the Illinois
Commercial Small Fruit and Grape Spray Guide contains no recommendations
specifically for the control of adult strawberry rootworms, postharvest
sprays of insecticides registered for other pests (in 1996, Guthion, Sevin,
or Thiodan) also control this insect. Unnecessary sprays should be avoided,
however, so that predaceous mites are not killed, leading to outbreaks
of spider mite populations.
strawberry rootworms occur in many fields, these pests do not damage berries
directly and often do not reach high densities. Consequently, controlling
them is often unnecessary. Insecticide applications for the control of
foliage-feeding pests can and should be based on scouting results, not
preventive spray programs.