How can I keep worms out of my sweetcorn ears? Also, what causes smut?
Question:I planted 82 day corn, so it's just starting to tassle. Last year I didn't have too many ears with worms, but someone told me to put vegetable oil on the silks and the worms won't bother them. Does this work or affect pollination? Any suggestions would be great. Thanks!
Answers:
Organic farmers are using multiple techniques to control european corn worms. Use Trichogramma ostriniae wasps as natural predators that attack the eggs of the European corn borer and an all-season pest, the fall armyworm. Spray Bt (a bacteria toxic only to caterpillars & worms) mixed with soybean oil directly on the corn silks.
Here is some very usefull information from North Carolina University: "Corn earworms are a major pest on corn. The night-flying, light brown- or buff-colored moth lays eggs on the corn silks. In North Carolina, the moth can emerge as early as late March. These tiny, dome-shaped eggs hatch in 1 to 2 days in warm weather or 10 days in cool weather. The small caterpillars move down the silk into the ear, where they feed on the tip. After 12 to 13 days, the caterpillars leave the ears by boring out the side or crawling out the tip. They burrow 3 to 5 inches into the soil to pupate. After about 12 more days, they can emerge to start the cycle again. There can be at least three generations per year, and the pupal stage can also overwinter.
Once earworm caterpillars have worked their way inside the ear, they cannot be controlled. Early plantings often are not affected by earworms, but late plantings can be under serious pressure. Low infestations are often handled by simply removing the damaged ear tip of the corn after harvest. Some growers provide a free "de-silking" of the ears at sale, so the consumer never sees the worms.
Earworm adult moths should be monitored by pheromone traps placed near the corn field. In Oklahoma, Kuepper and colleagues (1991) used oils and oil-pesticide blends to control corn earworm on small acreages. They injected oil into the neck of the ear (where the silk emerges from the husk), with a standard oiling can. To be effective, oil must be applied 2 to 3 days past the full-brush stage (when silks are at maximum extension from the eartip). Addition of Bt or pyrethrum is more effective than the oils alone. Be aware that using Bt with oil is difficult, time consuming, and not always effective. Estimates obtained for costs of these methods, however, are competitive with the conventional pesticide methods.
Fall armyworms can also be a major pest in North Carolina. They overwinter further south and migrate north each year. The female moths are about 1.5 inches across the wings with grayish-white hind wings and dark gray forewings with splotches and white spots near the tips. They deposit clumps of up to 150 pinkish-white eggs on the leaves. In warm weather, these eggs hatch in 3 to 4 days. In 2 to 3 weeks, the armyworms are about 1.5 inches long, light tan or green to almost black with yellow and dark stripes running the length of the body. Their distinctive characteristic is an inverted Y on the front of the head. Fall armyworms will feed on just about any plant, but damage is especially severe in late sweet corn and field corn. They will eat all above-ground parts of the plant and are very messy eaters. The best defense is to plant early so that corn matures in mid-August before armyworms peak in the fall.
Trichogramma wasps may provide some control of European corn borers, beneficial nematodes sprayed on the corn plant and silk may reduce earworm damage, and ladybugs will help control aphid populations."
Corn smut is caused by the fungus Ustilago maydis. The fungus causes gall formation on all aboveground parts of corn plants. Collecting and destroying infected ears before the dark fungal spores form will help reduce severity in small plantings. Crop rotation, in which corn is not grown more often than one year in three, will help reduce future fungal infections. The most effective control is to plant resistant hybrids. Many of the commonly used sweet corn varieties are susceptible to this disease. The White Sugary Enhancer varieties are more resistant to smut than either the White or Bicolor Supersweet varieties.
Smut is a fungus. As for as oil on the silk, I've never heard this. I would think it would affect polination but really don't know. If I were you, I do an experiment and try the oil on a few plants and see what happens. You should be able to tell if it affects polination by noting if those ears have fewer kernels of corn. You should also be able to tell if it helps to keep out the ear worms. Good luck
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