Consumer demand for damage-free sweet corn means that growers must develop the best possible management program for insect pests, especially those that attack the ear. |
Soil insects, primarily wireworms and white grubs, can cause stand reduction or stunted plants. These insects should be considered a serious threat when corn will be planted in ground immediately following sod. A preplant treatment may be considered. However, it is likely that a planting-time treatment will provide sufficient protection. Wireworms are on the label of most soil insecticides. These insects can be very numerous in scattered spots in a field. In these cases, damage may occur even when a soil insecticide is used.
Soil insect problems generally decrease with time out of sod. Problems with white grubs may occur in soils fertilized heavily with compost or manure. Rootworms may cause damage in ground where corn is grown every year. Soil insecticides will generally greatly reduce troubles with these pests
Soil insecticides that are banded over the row should be incorporated lightly in the top one-half to one inch of soil. These products are very toxic and should be used with great care.
European Corn Borer
Corn borer populations fluctuate from year to year and can be more severe in some fields than others. There are two generations of this insect each year.
The first generation occurs from early June to early July and is most damaging to early-planted corn. Damage is primarily due to borer tunneling in leaf midribs and the stalk. The second generation in August and September is a greater threat to late-planted corn. Borers of this generation tunnel in ears, ear shanks and stalks. Stalk breakage may be serious. Borer entrance holes in corn plants also provide a site for stalk rot pathogens to enter the plant.
The corn earworm is the most serious sweet corn pest because it feeds directly on the market product. Once worms have become established within the ear, control is impossible.
Earworms spend a relatively short period of their life feeding in a site that can receive an adequate insecticide application. Earworms are variable in color, but they have a brown head without markings and numerous microscopic spines covering their body. A preventive program, especially on late season corn, is necessary to ensure that damaged ears are at a minimum
Corn earworms overwinter as pupae in underground cells. Some adults from these pupae begin to emerge as early as late March, others may not appear until August. There are generally four generations each year, however, overlap is great and adult moths that can lay eggs may be present in significant numbers throughout most of the growing season.
Female moths search out green silks on which to lay single eggs. Following hatch, the small larvae often eat the egg shell before beginning to feed on the silk. Corn earworms generally complete their development in 14 to 16 days. Full grown worms leave the ear and pupate in the soil. The new adult will be active in another 10 to 14 days.
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