European Corn Borer
How to identify and control corn borer larvae using organic methods.
A major pest of corn, the European corn borer (Ostrinia nubilalis) will also feed on over 300 different garden plants including peppers, snap beans, potatoes, tomatoes, apples and gladiolus. Damage to corn is caused by the young larvae, which chew leaves and tassels. Later they tunnel all parts of the stalks and ears, resulting in reduced plant vigor, broken stalks, poor ear development and dropped ears. Other crops are damaged primarily by the tunneling of the stalks, pods or stems by the larvae.
Fully grown corn borer larvae (3/4 – 1 inch long) are extremely destructive, flesh-colored caterpillars with a reddish or dark brown head and several distinct spots on the top of each abdominal ring or segment. The adult borer is a night-flying, yellowish-brown colored moth (1 inch wingspan) with dark wavy bands across its wings.
Note : The European corn borer most likely arrived in the United States during the early 1900’s in imported broom corn which was used to make brooms.
Fully grown larvae pass the winter concealed in corn stubble or other plant parts on which they have been feeding. Pupation takes place in late spring, with the adult moths appearing in May and June. When mature, the females begin laying clumps of white eggs on the undersides of the lower leaves of host plants. (Adult females may lay up to 500 eggs over their short lifetime.) Under ideal conditions, these first generation eggs hatch within 3-7 days. Tiny caterpillars begin feeding on host plants and complete their development in 3-4 weeks. Pupation occurs deep inside the corn stalks and second generation moths emerge and begin laying eggs in early summer. Produces 1-3 generations per year depending upon the climate.
Note: Second generation borers are considered to be the most damaging to corn.
Corn Borer Control
Shred and plow under cornstalks in or near fields where borers overwinter. This should be done in fall or early spring, before the adults emerge. Use pheromone traps to determine main flight period for moths, then release trichogramma wasps to destroy eggs. Beneficial insects, such as ladybugs and lacewing larvae, will consume a large number of borer eggs. Spray Garden Dust (Bt-kurstaki) or Monterey Garden Insect Spray (spinosad) to kill young caterpillars. Repeat applications every 4-5 days until tassels turn brown. Use organic insecticides only as a last resort.
Note: Ladybugs will consume almost 60 borer eggs a day. Stink bugs, damsel bugs, spiders and hover fly larvae feed on young caterpillars.
Control nearby weeds to minimize the number of borers in your garden. Moths are attracted to these areas where they rest and mate, resulting in proportionately more egg laying. Planet Natural offers a large selection of organic herbicides that won’t damage your health… or your soil.
Photo Credit: Department of Entomology, Iowa State University