In northern areas, where corn earworm tends to be a late-summer problem, gardeners can minimize earworm woes by planting sweet corn early and growing tight-husked varieties, says Fern Marshall Bradley, author of Rodale’s Vegetable Garden Problem Solver and editor of New York Organic News.
Be wary of sweet corn cultivars labeled as earworm-resistant, cautions Bradley, noting that sweet corn that has been genetically modified with Bacillus thuringiensis var. kurstaki (BTK) has been developed for commercial use and may become available to home gardeners. Naturally resistant tight-husked varieties, which have long, close-fitting husks that extend past the tip of the ear and physically impede worms’ entry, include heirlooms such as ‘Country Gentleman’ and ‘Victory Golden’.
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For further protection against ear-worms, treat each ear with vegetable oil, Bradley recommends. Using an eyedropper or oilcan, drip five drops of oil into the tip of each ear just as the ends of the silks start to turn brown. Adding BTK, neem, or spinosad to the oil can make the treatment more effective. (Dilute according to label directions.) “Timing is important,” says Bradley. “Apply the oil too early, and it interferes with pollination, resulting in poor tip fill. Apply too late, and it won’t kill the caterpillars.
“Of course, a low-tech solution is simply to cut off the tips of infested ears at harvest time,” she notes. “Undamaged parts of the ears will be just as tasty and good as earworm-free corn."