Much of the sweet corn grown in the United States is sold as a fresh-market product, so it needs to be visually appealing to attract a buyer. Corn earworms can devastate the yield and appearance of the ear and are therefore a major concern for growers.
Adult corn earworm moths lay eggs on corn silks and on leaves, husks, and stems near the silks. After eggs hatch, larvae travel along the silks to feed on kernels, where they remain protected by the husks. Bt corn offers some protection against feeding by corn earworms, but some growers still conduct aerial spraying operations as often as once every 4 days to control the pest.
Bradley Fritz, an agricultural engineer at the Southern Plains Agricultural Research Center in College Station, Texas, conducted a study to see if aerial spray rates and droplet sizes make a difference in whether insecticides reach the target to control corn earworms. To be effective, the insecticides must penetrate the plant canopy and reach the silks, where larvae begin feeding soon after hatching.
Fritz sprayed test plots three times in June 2008 with insecticides approved for organic operations. He sprayed some plots with 400-micron droplets and some with 220-micron droplets. Insecticides were mixed with water at label-recommended levels and sprayed at rates of either 5 gallons or 9 gallons per acre. He and other ARS researchers then collected silks from ears of corn growing on the plots to assess how much spray actually reached the targeted silks.
Fritz’s results, published in the International Agricultural Engineering Journal, showed that higher spray rates with larger droplets worked best to ensure the insecticide reached the targeted corn silks.
The work is part of an ARS program to optimize aerial spraying technology to control corn earworms. The results will guide future corn earworm spraying operations, and the methods may be used in future studies of spray rates for other crops and pests.—By Dennis O'Brien, Agricultural Research Service Information Staff.
"Better Guidance for Battling Corn Earworm" was published in the April 2010 issue of Agricultural Research magazine.