As growers begin to prepare for planting this year's corn crop, decisions on the type of insect management program they choose should be made before putting the planter in the field.
Many of the insect pests associated with corn feed on the roots or the seed placed in the furrow. These include seed corn maggots, corn rootworms, fire ants, wireworms and grubs. Because they are associated with the soil, foliar applications of insecticides made after the corn emerges will give no control of these soil-inhabiting pests. Therefore, a soil-applied insecticide at planting is the only means of control.
The seed corn maggot, the larva of a small fly, will feed on the germinating seed in the soil. The fly will lay its eggs in the soil of fields that are high in organic matter. It is usually more of a problem in fields planted under cool, wet conditions.
Corn rootworms, wireworms and grubs feed on the developing root system of the corn plant. The Southern corn rootworm is the predominant rootworm species in Arkansas corn. The adult, also known as the spotted cucumber beetle, lays its eggs in cornfields in the spring. The small larvae attack and feed on the root system, causing the plants to lodge under heavy infestations.
It is difficult to predict from year to year which, or even if, these pests are going to be a problem. Results from research conducted by the University of Arkansas Cooperative Extension Service vary from year to year, with some years showing an economic benefit from an in-furrow insecticide application while in other years there is no benefit. Benefits depend on the pest populations present during that growing season.
Applying a labeled insecticide at planting is basically an insurance policy against these pests. Growers have a few new options to choose from this year. Gaucho and Premise are formulations of imidacloprid that have received a full label for use in corn this year. Furadan, Counter, Lorsban, Aztec, Dyfonate, Force and Regent are also still available as options to the grower. Growers should consult their local Cooperative Extension Service for current recommendations on insecticides and rates. Always read and follow label directions.
Variety selection is also important in managing insect pests in corn. Bt corn, which has been available for sometime now, gives excellent control of corn borers, pests which attack the corn stalk later in the season, causing lodging and yield losses. In recent years, the Southwestern corn borer has caused significant problems for Arkansas corn growers. The performance of the Bt corn varieties has been very favorable in controlling this pest.
Because corn borers are more of a problem in late-planted corn, growers should consider planting a Bt variety if planting is delayed towards the end of the recommended planting season. Plant non-Bt varieties first and save the Bt varieties for those later plantings.
Glenn Studebaker is an entomologist with the University of Arkansas Cooperative Extension Service.
E-mail: [email protected].