Southwestern Corn Borer

Injury and Pest Symptoms

Whorl-stage corn

First- and second-stage larvae feed 9 to10 days in whorl, creating pinholes and small, circular lesions or "windows" to large elongated holes
Third-stage larvae depart the whorl, crawl down the plant, and burrow into the stalk
Tunneling may damage the growing point, causing "dead heart" and stunted plants
Large larvae tunnel vertically in the stalk
Tunneling reduces uptake of nutrients and water, which stunts plant height and reduces grain yield

Reproductive-stage corn

Early-stage larvae feed between husk leaves, on ear shoots and behind leaf sheaths
Late-stage larvae may feed on kernels, often near base of ear, but eventually tunnel into stalk (photos below) and tunnel may be 12 inches long

In corn, 29% yield loss reported from stalk tunneling
Additional harvest losses of 50 to 75% can occur during fall when larvae girdle stalks, causing corn to lodge
Kernel feeding can increase aflatoxin levels in grain
In sorghum, up to 50% yield loss may occur

Common name: southwestern corn borer
Latin name: Diatraea grandiosella, family Crambidae
Description
- Adult: dull-white or buff-colored moth; wingspan 3/4 to 1 1/2 inches (19 to 38 mm)
- Larva: (summer phase) creamy white with large, raised brown or black tubercles on each body segment; (winter phase) creamy white and without distinctive spots; head black (instars 1 to 3) or reddish brown (instars 4 to 6)
- Egg: flat and oval, laid in clusters; pale yellow-green when first laid, but within 36 hours develops three orange-red lines (see below)

Similar Species

Life History

Larvae pupate in the spring inside cornstalks at the base of plants
Females lay up to 400 eggs on leaves, stalks, and ear husks
Eggs hatch in 4 to 7 days
Early-stage larvae feed in corn whorls, behind leaf sheaths, or on husk leaves, ear shoots, and kernels
Late-stage larvae tunnel into the stalk
Larvae complete 5 to 6 stages; summer generation requires 38 to 56 days
Overwintering (diapause) larvae crawl to base of stalk, tunnel inside, and create an internal girdle
Larvae are cannibalistic; usually only one larva overwinters in base of stalk
2 to 3 generations occur each year depending on elevation and latitude
Fungus, Beauveria bassiana, may kill 50% of larvae

Bt Corn Hybrids

Pioneer® brand products containing a corn borer trait provide excellent control; contact a Pioneer representative for trait availability

Non-Bt Corn Hybrids

Plant early: More mature plants are damaged less by 2nd and 3rd generation larvae Pioneer® brand products containing a corn borer trait provide excellent control; contact a Pioneer representative for trait availability
Scout fields: Economic threshold is 20 to 25% of plants infested with eggs or young larvae; pheromone traps can predict moth flight and time to scout; contact state extension entomologist for resource information and scouting procedures
Insecticides: Application of insecticide must occur before larvae tunnel into stalk; contact your state extension entomologist for recommended insecticides
Postharvest crop destruction: Stalk shredding and minimum tillage that breaks the stalk at ground level reduces overwintering survival

Photos and Text

Marlin E. Rice (Pioneer); Reviewed by Scott Stewart (University of Tennessee), and Paula Davis and Herb Eichenseer (Pioneer)