While tilling my perennial beds this spring, I noticed small orange-yellow, worm-like insects (roughly 1/8 inch in diameter and 1 inch long). What are they? Are they good guys or bad guys?
Sounds like you’ve got a crop of wireworm (Limonius spp.) larvae crawling in your perennial bed. These larvae are more foes than friends. Wireworm larvae are slender, orange-brown creatures with three pairs of short legs close to their head. They can be up to 1 inch long. The larvae have a small knob toward their rear on the underside. Larvae damage or kill plants by devouring seeds and boring into roots, tubers, and bulbs. Their appetite for gladiolus corms, potatoes, and carrots, among others, is heightened in soil previously planted with lawn grass.
Adult beetles, unlike their progeny, feast on leaves and flowers but cause little damage. These hard-shelled, elongated, dark-colored, 1/3- to 3/4-inch long beetles are also called click beetles because they make a clicking noise as they flip over from back to front. Every spring, females lay eggs on plant roots. Although the eggs hatch in 3 to 10 days, wireworm larvae spend the next two to six years dining on roots, tubers and bulbs in the spring and fall. They burrow deeper into the soil during the winter. Once mature, the larvae pupate in late summer.
You can manage the wireworm larvae population by working an appropriate insecticide into the top 6 to 8 inches of soil. Some experts suggest burying raw potato pieces 4 to 6 inches deep to attract larvae, checking the potatoes every other day to destroy the larvae. Applying parasitic nematodes to soil could also discourage these larvae.