The Vegetable Garden

Corn - Harvesting


    Each cornstalk should produce at least one large ear. Under good growing conditions (correct spacing; freedom from weeds, insects and disease; and adequate moisture and fertility), many varieties produce a second ear. This second ear is usually smaller and develops later than the first ear.

    Sweet corn ears should be picked during the "milk stage" when the kernels are fully formed but not fully mature. This stage occurs about 20 days after the appearance of the first silk strands. The kernels are smooth and plump and the juice in the kernel appears milky when punctured with a thumbnail. Sweet corn remains in the milk stage less than a week. As harvest time approaches, check frequently to make sure that the kernels do not become too mature and doughy. Other signs that indicate when the corn is ready for harvest are drying and browning of the silks, fullness of the tip kernels and firmness of the unhusked ears.

    To harvest, snap off the ears by hand with a quick, firm, downward push, twist and pull. The ears should be eaten, processed or refrigerated as soon as possible. At summer temperatures, the sugar in sweet corn quickly decreases and the starch increases.

    Cut or pull out the cornstalks immediately after harvest and put them in a compost pile. Cut the stalks in one foot lengths or shred them to hasten decay.

    Common Problems

    Corn earworms are a problem in sweet corn every year. Earlier plantings are not badly infested in areas where the pest does not overwinter, but later harvests usually have severe earworm damage unless timely control measures are followed. Corn earworms deposit eggs on the developing silks or on the leaves near the ear. The tiny caterpillars follow the silks down into the ear, where they feed on the tip. Only one corn earworm will be found per ear because the caterpillars are cannibalistic, with the largest devouring any others present. Once the worm is inside the protective husk covering, there is no effective control. Anything that restricts the worm-such as tightening the tip of the husk with a rubber band or clothespin after the silk appears, or inserting mineral oil (1/2 medicine dropperful) in the silk tube-helps to decrease the damage.

    Corn rootworm beetles may cause extensive silk damage that interferes with pollination. Later plantings usually suffer the greatest damage, especially where field corn is grown. Beetles multiply in early plantings of field corn, mature and migrate to plantings of young, tender sweet corn. Silk and the young, tender, green leaves are preferred feeding sites. If infestation is sufficient to remove silk before pollination, cobs develop without a full set of kernels. Control measures must be taken as the silk emerges.

    European corn borers damage stalks, tassels and ears. As their name indicates, corn borers bore into the plant; and the stalks break over when damage is severe. Corn borers also may bore into the cob and be found after cooking. A suggested insecticide can be applied at 5 day intervals, beginning when eggs hatch in June. Spray applications for earworms usually give adequate control of corn borers.

    Flea beetles often attack early in the spring as the corn plants emerge through the soil. Flea beetles can be quite damaging when numerous and they may carry Stewart’s bacterial wilt disease.

    Stewart’s wilt is a bacterial disease spread by the flea beetle. This disease causes yellow streaks in the leaves, stunting and death of young plants of susceptible varieties. The disease occurs more frequently in the southern states and is not severe after cold winters or when resistant varieties are planted. If possible, plant varieties with good resistance.

    Smut is caused by a fungus that invades the kernels. It develops as a swollen black pustule (gall) in the ear and sometimes infects the tassel. Some sweet corn varieties are more tolerant to smut than others. Smut occurs most frequently on white varieties and is often severe when extremely dry or hot weather occurs just before and during tasseling. Remove and destroy smut galls while they are moist and firm. Do not discard these galls in or near the garden. Place in the garbage or burn them. The smut is not poisonous, but it is unpleasant to handle. Break off the infected part of the ear. The remainder is suitable for eating.

    The immature smut fungus or "maize mushroom" is highly prized in Mexican cooking. Harvest when the fungus is expanded, but before it becomes black and dried out. The time generally is about 2 to 3 days before the sweet corn reaches peak eating quality.