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Earworms are the bane of sweet corn farmers

Posted: August 23, 2014 - 11:22pm

One of my favorite foods from the summer garden is sweet corn. Sweet corn is fairly easy to grow, but many people find an infestation of the corn earworm when it comes time to shuck the ears. The corn earworm is one of the most common corn pests in the state of Georgia. These insects can be found in just about every field where corn is planted. In some untreated fields, corn earworms can feed on 90-percent or more of the ears.

Corn earworms overwinter as pupae(the transformation stage between the larva to adult). Corn earworm adults emerge as early as late March while others may appear in late August. There are generally four generations each year. Therefore, overlapping generations of adult moths laying eggs can be present throughout most of the growing season. Corn earworm moths lay eggs on the leaves of small corn plants. The worms hatch out and move into the whorl of the corn plant and begin feeding on foliage. The larvae then cover themselves with a plug layer of frass, or excrement, which protects them from predators and pesticides. These early infested corn plants usually end up with tattered leaves.

Corn planted later in the season is in danger of ear damage. Later generations of corn earworm moths lay their eggs directly on the corn silks. Several eggs will be laid on the silks, but only one will make it to the corn ear. Corn earworm damage shows itself as tiny trails of missing kernels and excrement. They also affect tomato plants, where they eat buds, chew holes in the leaves and will even bore into the fruit.

To control corn earworm on your sweet corn, you have both chemical and organic options available. If your garden plot is small enough, you can use the organic method of mineral oil control. Using a dropper, apply five drops of mineral oil to each corn ear tip when the silks begin to turn brown. This usually occurs five to six days after silk emergence. If you apply the mineral oil too early, you can disrupt pollination, so make sure to wait for silk browning. Research also shows that adding Bacillus thuringiensis (B.t.) to the oil will improve earworm control. For larger plots of sweet corn, the mineral oil method is just too labor intensive.

Conventional insecticides, such as carbaryl, bifenthrin and even the bacteria-derived Spinosad can be used against corn earworms. Apply spray solutions when the corn first begins to silk and repeat every two days until the silks have wilted. Spray should be directed at the corn ears.

Your third option is to simply do nothing. If a corn earworm infestation is found, you can simply use a knife to cut off the damaged parts of the ear. The rest of the ear will still be suitable for consumption.

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