Issue No. 7, Article 3/May 7, 2004
Southern Corn Leaf Beetle
An early-season pest that has generated much attention this past week is the southern corn leaf beetle. Several reports of potential injury caused by this insect have filtered in from western and west-central Illinois. The southern corn leaf beetle becomes active in early spring, feeding on weeds such as cocklebur and early-planted corn.
Southern corn leaf beetles overwinter as adults. In the spring, adults feed, mate, and lay eggs in the soil near corn plants or weeds. Larvae hatch in approximately 10 days and feed on corn roots--from May until mid-July in the central portion of the Corn Belt. Adults emerge in cornfields and feed for a short period of time before seeking overwintering sites.
Adults may be difficult to find in early spring. They are approximately 3/16 inch long, dark gray to brown, and often covered by clumps of dirt. When disturbed, the beetle drops to the ground and remains motionless, making it difficult to find in the field. The adults feed mostly early in the morning, late in the evening, at night, or on cloudy days.
Southern corn leaf beetle feeding on seedling corn leaves (photo courtesy of Kevin Black, Growmark).
Injury caused by the southern corn leaf beetle may resemble early signs of cutworm injury. Adult beetles feed on leaves and stems of corn plants, chewing characteristic notches out of the edges of the leaves and giving them a ragged appearance. If seedlings are small, the notches the beetles chew in the stems may cut the plant off, resembling cutworm injury. Sometimes the beetles feed in such large numbers that injured plants die. Corn growth that is slowed by environmental conditions can exacerbate damage caused by the insect.
Injury caused by southern corn leaf beetles (photo courtesy of Mike Roegge, University of Illinois Extension).
Two southern corn leaf beetle adults (circled) on the soil surface in a cornfield.
Decisions about whether to control southern corn leaf beetle infestations with insecticides are difficult to make. Because of the beetles' ability to escape notice, correct identification and assessment of injury can be a challenge. There is no economic threshold established for control of the southern corn leaf beetle. Insecticides suggested for control of southern corn leaf beetles are Baythroid 2 (1.6 to 2.8 oz), Capture 2EC (2.1 to 6.4 oz), Discipline 2EC (2.1 to 6.4 oz), Lorsban 4E (1 to 2 pt), Mustang Max (2.72 to 4 oz), and Warrior (3.84 oz). These are all restricted use insecticides. Please follow all label instructions and precautions.--Kelly Cook and Kevin Steffey