Sweet corn takes up more garden space than most crops and it’s also fairly demanding in terms of moisture and nutrients. The incomparable taste of freshly-picked corn, though, is enough to encourage gardeners to continue to grow it.
Native to Central America, sweet corn (Zea mays) has been cultivated in North America for thousands of years. This annual garden plant is generally disease and pest resistant, but if problems do take hold in your corn patch, the consequences can be devastating. Since corn grows so fast, it’s hard to control diseases and pests with chemicals.
Corn must be planted in rich, fertile soil and in full sun. Amend the soil with aged compost or manure several months before planting. Plant corn in blocks containing at least four rows so the wind can pollinate it efficiently.
Plant the seeds two or three weeks after the last expected frost. Corn won’t germinate in wet, cold soils and does best in soils that are 60 degrees or warmer.
Plant seeds 1 to 1 ½ inches deep and 3 inches apart. Thin the stalks to 18 inches apart when they stand 3 inches tall. Sidedress corn plants with a nitrogen-heavy fertilizer every six weeks during the growing season and keep the soil evenly moist. Use a soaker hose system rather than overhead sprinklers. If water splashes on the tassels at the time of pollination, the ears won’t pollinate well and will have fewer kernels.
Corn smut is probably the most common corn disease. This fungal disease lives in the soil and causes unsightly gray or white growths, or growths, to form on the ears, leaves and stalks. In Central America, the galls are considered a culinary delicacy, but most gardeners find them unappealing at best. To control corn smut, remove the galls when they’re small and immature. Place them in a sealed plastic bag and discard. Work carefully so you don’t cause the spores to spread to other corn plants.
The fungus that causes corn smut can live in the soil for two years, so rotate crops and avoid planting corn where you’ve previously had problems. Corn smut is more prevalent during periods of high heat and moisture. Plants grown too closely together are also more susceptible.
Rust is another common disease, although it rarely causes serious damage. Plants affected with rust might have orange or red spots on the leaves. The spots are usually temporary and disappear as the plants mature. Rust occurs most often in cool, moist weather.
Stewart’s Wilt is a viral disease spread by flea beetles. The main symptom is brownish streaks in the leaves that eventually spread to stunt or kill the entire plant. Once infected, corn plants almost always succumb to this disease. There are no chemical controls. To minimize problems, rotate crops because the flea beetles overwinter in the soil and spread the disease when they feed on young plants. Control the flea beetles with rotenone or spread agricultural lime or wood ash on the soil.
Seed Rot Disease is caused by soil-borne fungi. Seeds might not germinate and any emerging seedlings are stunted. Seed rot diseases are most common in cold, wet soils. Seeds germinate slowly in these soils, so they’re more at risk of exposure to the fungus. Plant high-quality corn seeds only after the soil has warmed in the spring. If you’ve had problems in the past, consider buying corn seeds that have been treated with a fungicide.
Root Rot, like seed rot disease, is most common in wet soils. As the roots rot, the corn stalks may also begin to rot, causing the entire stalks to fall over and die. To prevent root rot, plant corn seeds in well-draining soil that has been amended with compost. Space corn plants so air circulates freely and use soaker hoses instead of overhead sprinklers. If your soil is very heavy, consider using raised beds.
Southern corn leaf blight causes bleached or discolored spots on both the corn ears and the leaves. Pull up and discard infected corn plants. Rotate crops and clean up the garden immediately after harvest.
Nematodes are microscopic roundworms that feed on the roots of plants in the garden. The first sign of nematodes is usually stunted growth and pale leaves. Pull up the plants and you’ll see nodules or growths on the roots. A soil test can confirm the presence of nematodes. If you’ve had a problem with nematodes, be sure to rotate crops and clean up the garden well. In some cases, you might have to solarize the soil. To solarize the soil, spread a clear sheet of plastic over it during the hottest months of summer. Secure the plastic so it sits tightly over the soil and leave it in place for six weeks. The heat generated by the plastic destroys any nematodes in the soil. Unfortunately, it also destroys beneficial microbes. Add compost and aged manure to the soil after solarizing to rebuild it.
Corn earworms are a common pest in the corn patch. Adults lay their eggs on the corn silk. Once the larvae hatch, they crawl into the corn ears and begin feeding. You can handpick corn earworms and drop them in a bucket of soapy water or try putting a few drops of mineral oil on the tops of the ears. The mineral oil runs into the ears, covers the earworms and smothers them.
Corn borers are caterpillars that tunnel through the stalks and ears, causing extensive damage. Walk through the garden frequently and handpick any you see. Drop them in soapy water.
Raccoons, squirrels, and crows are definitely on the most wanted list when it comes to pests in the corn patch. Raccoons and squirrels, in particular, can strip all the ears off the plants in just one or two nights. To thwart them, don’t plant corn near fences, trees, or buildings. Squirrels can jump from these surfaces directly on the corn plants and knock them down. Plant squash underneath the cornstalks. Raccoons and squirrels don’t like to walk across the prickly vines. Some gardeners spread crumpled aluminum foil on the garden soil. You can also use motion detecting lights and sprinkler systems, or a well-trained dog.