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YieldGard fights corn rootworms
By Daniel Davidson
DTN Agronomist
OMAHA (DTN)--Controlling the western, northern and southern corn rootworms requires a management strategy. Historically, growers controlled corn rootworm by using crop rotation and insecticides. Today, Monsanto's YieldGard Rootworm trait is available.
The western corn rootworm (WCR) can significantly affect corn production either by feeding on roots, leaves or silks. When larvae feed on corn roots, they reduce yields and predispose the roots to stalk rot and the plants to lodging. Adults feed on the developing silks, which may prevent pollination, causing missing kernels and severely reduced yields. Rotating crops is the most consistent and economical means of controlling rootworms. Corn rootworms must feed on corn roots to develop and mature properly.
If they hatch in a field rotated out of corn, they will starve to death because they cannot move more than 10 to 20 inches in search of food. First-year corn will not require an insecticide to control the rootworms that hatch from the few eggs that might be left over from the previous corn crop.
There are commercial rootworm-resistant corn hybrids containing the Bt gene, including YieldGard Rootworm. This transgenic hybrid is very effective in controlling corn rootworm larvae. Planting Bt corn that protects the corn from rootworm is a preventative measure. Growers need to remember to select hybrids adapted to their area.
Any practice that encourages rapid plant growth helps reduce rootworm damage. Early planting often maximizes yield and allows silks to develop before peak rootworm beetle feeding.
Most insecticides have targeted the larval stage. A variety of insecticide formulations and application methods are available. Liquid or granular insecticides may be applied at planting or at cultivation.
Some fields in continuous corn will have rootworm populations large enough to justify the use of an insecticide.
Continuous corn fields that were not scouted during the previous growing season also should be protected with an insecticide. If a field is to be treated, then one of several recommended application methods must be selected. Applications methods include treating the seed with an insecticide, planting granular insecticides in-furrow or banded over the row either at planting or cultivation or applying liquid insecticides at planting or at cultivation in a spray directed at the base of the plant.
Adult corn rootworm control programs suppress corn rootworm beetle populations and reduce egg-laying so larval populations the following season will not cause economic loss. They can also prevent silk-clipping damage that may interfere with pollination.
Date: 5/11/04
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