Southern Cornstalk Borer
Diatraea crambidoides (Grote), Pyralidae, LEPIDOPTERA


DESCRIPTION

Adult - The adult is a straw-colored or dull white moth with a wingspan of 15 to 40 mm (females larger than males). The forewings are slightly darker than the hind wings.

Egg - The flat, elliptical egg, approximately 1.3 mm by 0.8 mm, is creamy white when laid but later develops an orange hue due to the presence of three transverse, orange-red lines. Color plate.

Larva - The full grown larva is approximately 25 mm long. The winter form is creamy yellow with a dark brown head. The summer form is milky white and covered with black spots, each bearing a short, dark bristle. Color plate.

Pupa - About 22 mm long, the pupa is the same color as the larva when first formed but later changes to a reddish-brown.


BIOLOGY

Distribution - The southern cornstalk borer occurs from Alabama and northern Florida to Ohio and Maryland. A 1974 survey in North Carolina revealed that infestations rarely occur in the mountain counties.

Host Plants - The southern cornstalk borer attacks corn, grain sorghum, sugarcane, broomcorn, and Johnson grass.

Damage - Young caterpillars feed within the plant whorl. As the leaves unfold, rows of irregular holes may appear. Larvae also tunnel in the midribs of leaves, and sometimes destroy growing points within leaf whorls. As larvae grow larger they tunnel into stalks. Tunnelling may be extensive in the lower portion of the stalk, primarily just above the soil line and into the taproot. This damage may be very destructive because of reduced nutrient and water uptake. Often the southern cornstalk borer is not noticed until severe stalk damage has occurred.

Life History - Southern cornstalk borers overwinter as larvae within cavities in corn taproots. In March or April, they change into pupae. Approximately 10 days later, moths emerge, mate, and begin laying eggs at night, usually on the underside of lower leaves. The flat eggs are laid either singly or in small clusters of 2 to 25 overlapping one another like shingles. When the eggs hatch 7 to 10 later, larvae move into the whorl of the plant, feeding on the leaves and spinning a silken thread behind them. Third- or fourth-instar larvae move down the stalks and eventually tunnel inside not far above the ground. In the summer, southern cornstalk borers live from 20 to 35 days and develop through seven instars. Mature larvae seal off the tunnels with frass and form cells in which to pupate. Summer pupation occurs in the above- ground stalk; pupation of the hibernating generation occurs in the base of the stalk or in large roots. Southern cornstalk borers have two generations per year.


CONTROL

Disc fields in the fall to reduce overwintering populations. Southern cornstalk borers cannot survive the winter in uprooted exposed stalks. Two years of successive corn crops on the same land usually enhance cornstalk borer populations; therefore, crop rotation is recommended. For specific information on insecticides and rates, consult the current North Carolina Agricultural Chemicals Manual.