Southern Corn Rootworm, Western Corn Rootworm, and other Chrysomelid
Roberts, P. M. and G. K. Douce, Coordinators. 1999. Weevils and Borers. A County Agent's Guide to Insects Important to Agriculture in Georgia. University of Georgia, Col. Ag. Env. Sci., Cooperative Extension Service, Tifton, GA, USA. Winter School Top Fifty Agricultural Insect Pests and Their Damage Sessions, Rock Eagle 4-H Ctr., Jan. 20, 1999.
Chrysomelid rootworms of concern to Georgia crops include the Southern corn rootworm (Diabrotica undecipunctata howardi Barber) and Western corn rootworm (Diabrotica virgifera virgifera LeConte).
Larvae of Chrysomelid beetles such as the spotted, striped, and banded cucumber beetles live in the soil and feed on the underground portions of certain plants. The western corn rootworm has been found in North Georgia in recent years. Larvae of all species are very similar in appearance: white, with the head and last abdominal segment black. At first glance, it is often difficult to tell which end is the head. Larvae are generally very fragile and easily pulled apart.
Rootworms may be found feeding on a wide variety of plants but are most damaging to cucurbits, corn and peanuts.
Larvae usually feed on roots resulting in weakened, stunted plants. Damage to corn roots will make plants more susceptible to lodging. Peanut pods can also be damaged causing reduced yields. Cucurbits may be further damaged when rootworms vector bacterial wilt. Maize chlorotic mottle virus may also be transmitted to corn.
Life cycles of rootworms are about 30-40 days with about 3 weeks in the larval stage. Adults lay eggs on the soil surface near plants. Larvae burrow into the soil and underground portions of the host plant. Pupation occurs in the soil. Adults emerge and feed on plants causing significant damage on some.
Rootworm damage is most common in heavy, damp soils. Any cultural practices that helps dry the soil surface will reduce survival of rootworm eggs and early-instar larvae. Soil insecticides are effective if applied at the proper time. Control of adult beetles, either intentionally or with insecticides targeting other pests, will also reduce the number of larvae in the soil.