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Corn Growing Problems: Troubleshooting

Corn in garden1
Corn growing
To come to harvest quickly corn requires warm temperatures, rich soil, and even, regular watering. Corn is wind-pollinated so planting in blocks or multiple rows to ensure pollination is important.

To come to harvest quickly corn requires warm temperatures, rich soil, and even, regular watering. Corn is wind-pollinated so planting in blocks or multiple rows to ensure pollination is important.

Here is a troubleshooting list of possible corn growing problems with control and cure suggestions: (Read to the bottom of this post for corn growing success tips.)

Corn Problems and Solutions:

• Corn does not emerge. Soil may be cold or damp. Plant later when the soil and temperatures are warmer; make sure soil is well-draining by adding aged compost and organic matter to soil.

• Insides of seed and young plants are eaten. Corn wireworm or the seed corn maggot is eating the seed. The corn wireworm is the larvae of the click beetle; the click beetle is reddish brown or black to ¾ inches long. Wireworms are brown or yellow and leathery to 1½ inches long. The seed corn maggot is a yellowish-white legless maggot, the larvae of a fly. The maggot feeds on the inside of sprouting seed. Cultivate the planting bed in fall to expose larvae to birds. Spade the corn bed and let it lie fallow every third season. To trap: use pieces of potato on a spike setting them 2 to 4 inches into the soil; check the traps twice a week. Pick and destroy wireworms and maggots from the potato.

• Seedlings are cut off near the soil surface. Cutworms are gray or brown grubs that hide in the soil by day and feed at night. Handpick grubs from the soil at the base of plants. Remove weeds and keep the garden free of plant debris. Place a 3-inch cardboard collars around the stems of seedlings and push the collars 1 inch into the soil.

• Seedlings are uprooted. Crows and birds will pull up seedlings to feed on seed. Cover seedlings with bird block or row covers until they are established.

• Stalks fall over. European corn borers are grayish pink caterpillars with dark head (more below); they can tunnel through stalks and weaken them. Use Bacillus thuringiensis and garden cleanup to control borers. Too much nitrogen also can leave stalks lush and green but weak. Test soil. Adjust fertilization. Avoid using fertilizers too rich in nitrogen. Feed plants with aged compost.

• Stalks and leaves deformed, bent over, or may fail to unfurl; plants are stunted. Aphids are small soft-bodied insects–green and gray–that cluster on undersides of leaves. Aphids leave behind a sticky excrement called honeydew; black sooty mold may grow on honeydew. Spray away aphids with a blast of water; use insecticidal soap; aluminum mulch will disorient aphids. Aphid predators include lacewing flies, ladybugs, and praying mantis.

• Tiny shot holes in leaves. The corn flea beetle can riddle leaves with small holes and transmit Stewart’s wilt, a bacterial disease that leaves the plant’s vascular system clogged with slime; infected plants wilt, become stunted and die. Pick off beetles; cultivate the garden to disturb the insect life cycle. Spray with pyrethrum or rotenone.

• Large holes in leaves. Armyworm, corn earworm, various beetles, and grasshoppers eat corn leaves and foliage. Handpick insects and destroy or place them in soapy water. Loss of small amount of leaf tissue will not reduce yields. Plant early corn varieties to avoid armyworms. Use commercial traps with floral lures. Cultivate in the fall to expose larvae.

• Holes in leaves near whorls. European corn borer; larvae are light brown to pinkish caterpillars with dark brown heads and dark spots on the body; adult moth is light brown with a ¾-inch wingspan. Larvae feed on corn whorls then bore into stalks. They also feed on tassels and kernels. Handpick and destroy larvae. Apply Bacillus thuringiensis. Remove and destroy all infested stalks at the end of the season.

• Leaf edges roll inwards. Soil moisture may be inadequate. Corn makes rapid growth after ears form and begins to mature; this requires consistent moisture. Water corn deeply, up to 2 or 3 hours at a time. When soil dries to a depth of 4 inches, water again. Place 2 to 3 inches of organic mulch on planting bed to conserve moisture.

• Leaves are mottled and streaked yellow and green; leaves yellow and die along the margins; growth is slowed or stunted. Mosaic virus and maize dwarf mosaic virus has no cure. It is spread by beetles. Plant mosaic virus-resistant varieties. Destroy infected plants and keep weeds and grasses down that host aphids beetles. Do not handle healthy plants after infected one.

• Yellow striping on leaves. Stewart’s wilt is a bacterial disease that results in the plant’s vascular system becoming clogged with slime; infected plants will yellow, wilt, become stunted, and die. Control flea beetles which spread the disease. Pick off beetles; cultivate the garden to disturb the insect life cycle. Spray with pyrethrum or rotenone.

Plant tolerant varieties.

• Leaves have purple margins starting with leaves at the bottom of the plant; plant may be stunted. Phosphorus deficiency. Perform a soil test; add bonemeal to the top of the planting bed at a rate of 2 to 3 pounds per 100 square feet. Use a commercial fertilizer rich in phosphorus 5-10-5 is good.

• Reddish-brown blisters on the top of leaves and stalks; leaves may turn yellow. Rust is caused by a fungus; rusty-colored spores grow on the plant. Rust favors warm, humid weather. Plant rust-resistant varieties. Avoid overhead irrigation. Prune away infected leaves.

• Grayish or tan oval spots on leaves. Northern corn leaf blight and southern corn leaf blight are fungal diseases that favor wet conditions. Add aged compost or organic material to planting beds to keep soil well-drained. Avoid overhead irrigation. Keep garden clean of debris and weeds which can harbor fungus spores. Plant resistant varieties.

• Leaves yellow as tassels form. Insufficient nitrogen. Side dress plants with aged compost. Water with compost tea or fish emulsion. Add aged compost to planting beds in advance of planting.

• Gray-white gnarled growths or galls on ears and leaves. Corn smut is a fungus disease. Remove and destroy galls as soon as found when they are still white. Do not allow black powdery spores from galls to fall into soil. Plant resistant varieties. Problem is more common in late harvests.

• Ears only partly filled, silks are chewed short or clipped off. Earwigs, Japanese beetles, and corn rootworm beetles feed on silks which prevents pollination or causes poor kernel development. Check ears daily for earwigs and beetles; handpick and destroy. Spray plants with hot pepper and garlic repellant. Place traps around the garden to collect pests. Keep garden free of weeds and debris.

• Incomplete kernel development; ears partially filled with ripe kernels; shriveled kernels. Each individual kernel must be pollinated; kernels that don’t receive pollen will not fill out. Pollen from male tassels must reach the female silks. Several possible causes: (1) Poor pollination can happen when not enough plants are planted; plant at least 3 to 4 rows at least 8 feet long. (2) Hot weather or high winds during pollination. Pollen sheds 2 to 3 weeks before harvest. (3) Insufficient soil moisture; keep corn evenly moist especially from silking to harvest. (4) Inadequate fertilizer or soil fertility; add aged compost to planting beds. Check for potassium deficiency. Plant varieties adapted to your area. (5) Birds are eating kernels; put paper bags over ears after pollination.

• Worms eat down through kernels; ears look brown and eaten. Corn earworm is a brown-headed caterpillar with lengthwise stripes to 2 inches long; the adult is a night-flying moth with brownish or olive wings and bright green eyes. The worm finds its way into the whorl of the corn plant to burrow down and eat developing tassels. Apply 20 drops of mineral oil just inside the ear tip 3 to 7 days after silks first appear. Break off the wormy end of ear and discard. Plant early-maturing varieties to avoid earworms; varieties such as ‘Country Gentleman’, ‘Golden Security’, and ‘Silver Cross Bantam’ have long, tight husks. Use commercial traps. Handpick caterpillars and destroy. Dust with Sevin.

• Stalks produce small ears. Plants are spaced too close together; plant early varieties at least 8 inches apart; space later varieties 12 to 15 inches apart.

• Popped kernels, kernels look like popcorn. Seed coats will sometime break at the weakest point. No cure. Plant another variety.

• Kernels are pink and moldy; brown lesions on stalks near joints; stalks rotten inside. Fungi can cause rots. Keep garden free of plant debris and weeds that can harbor fungus spores. Remove diseased plants. Make sure soil is well-drained; add aged compost to planting beds twice a year. Keep soil evenly moist but not wet.

Corn Growing Success Tips:

Planting. Grow corn in full sun. Corn requires moist, well-drained soil rich in organic matter. Prepare planting beds or planting mounds with plenty of aged compost. Additionally, sprinkle planting beds with nitrogen-rich cottonseed meal or soybean meal, about 3 pounds per 100 square feet. Plant corn in mounds or hills–thin each hill to 3 plants–or in raised beds. Mounds and raised beds warm early in the season and are well drained.

Block planting. Plant corn in blocks or short, multiple rows. Space plants about 15 inches apart with at least 4 rows and at least 4 plants in each row. Block planting will improve pollination; corn drops pollen from its tassels down to the silks in the ears below. Planted in a block, corn pollen that drifts on the breeze is more likely to find its way to an ear and silks below.

Plant time. Sow corn in the garden after the last frost in spring; it is best to plant corn when the soil has warmed to at least 62°F. Succession plant corn every two weeks for a continuous harvest. Corn can be started indoors 3 to 4 weeks before planting out; start seed in biodegradable pots so that roots are not disturbed when transplanted.

Care. Corn requires even, regular watering. Use a soaker hose to keep corn moist, about 2 inches of water each week. Add 1 to 2 inches of mulch between stalks to conserve soil moisture. Side dress corn with aged compost or a balanced fertilizer 1 month after planting and again when the tassels form.

Harvest. Begin picking corn 3 weeks after the first silks appear. When silks brown and begin to dry the corn is ripe. Check the ears to see that they are filled to the tip with kernels. To further test for ripeness, press a kernel with your fingernail, if the juice is milky white the ear is ripe.

More tips: How to Grow Corn.

Written by Stephen Albert

Stephen Albert is a horticulturist, master gardener, and certified nurseryman who has taught at the University of California for more than 25 years. He holds graduate degrees from the University of California and the University of Iowa. His books include Vegetable Garden Grower’s Guide, Vegetable Garden Almanac & Planner, Tomato Grower’s Answer Book, and Kitchen Garden Grower’s Guide. His Vegetable Garden Grower’s Masterclass is available online. Harvesttotable.com has more than 10 million visitors each year.

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  1. My daughter and I decided to try corn this year. We prepared our raised bed properly. Have about 20 stalks. They looked great but now are all falling over at the base. Not seeing signs of corn grubs. It is ok just to prop these up? Is there another issue I should be looking at?

    • Corn is shallow-rooted and it will appreciate any support you give it. You can mound up more soil around the base of the plant to help the roots get a better foothold. You can also place long supports such as bamboo stakes next to each plant and tie them in with elastic garden tape. Corn planted close together in blocks will often support each other.

    • See the article How to Grow Corn; the first photo of that article shows tassels emerging from the top of each corn ear. Tassels are green when young and as they age they turn brown. They are called tassels because they look like tassels. how to grow sweet corn

  2. Hello, I grew my corn seed in peat pots and then transplanted half into a raised bed of compost in my glasshouse and the other half into a raised bed of topsoil outside the glasshouse. All the raisedbeds outside have the same topsoil; All my parsnips and carrots, leeks and onions and beetroot are growing really well. However the corn I planted outside in the same topsoil has almost gone white and is very sickly looking ; as opposed to the greenhouse corn which is lush and dark green and growing vigorously. My first obvious thought was that the soil is deficient as it is only topsoil, however, all the other produce is growing just fine in it. i have sprinkled dried stable manure, worm castings and sheep pellets amongst the plants outside three days ago, will this be enough to rescue the corn? or shall i be better to just rip it out and start again? This is mid spring in new zealand as i write this question. sorry it was sooooo long. I look forward to your advice 🙂

    • If the problem was a lack of nitrogen, the organic fertilizers you have added should green up the plants in short order. If the plants do not turn around in 5 days, plant again. Make a checklist of other possible problems: (1) night temperatures dipped; (2) plants were over or under watered; (3) herbicide drift; (4) an animal disturbed the planting area; (5) a chemical or synthetic fertilizer hit the plants. A bit of detective work may under the cause.

  3. Hello,

    I have a question regarding corn smut. I’ve just found two galls growing from the bottom of the stalk of my only corn plant. Given the galls are still withish in color (no black in sight) should I get rid of the entire corn plant or just carefully remove and dispose of the galls?
    My corn plant hasn’t produced any corn yet, but other than the two galls I’ve found, the rest of the plant seems healthy enough.
    Thank you.

  4. I have a very small field for self picking of sweet corn eaten off the cob in the field. When all has been eaten how do i remove the dry storks in easiest manner?

    Or is it best to leave them in field?

    • Corn is shallow-rooted; you can remove it easily. The stalks do not compost quickly. Chop them up if you plan to put them in the compost pile or if you plan to turn them under to decompose.

    • Feed the plants with a dilute solution of fish emulsion every 10 days. Check the variety you are growing; you may be growing a miniature variety that will not put on much more height.

    • Insects, birds, and other varmints may find seedling leaves tasty. If the tops of the seedlings have been nipped off, they will likely not regrow. The surest strategy is to resown the seeds and cover the seedbed with a floating row cover which will exclude many insects and birds. Once plants get 4 to 6 inches tall, you can remove the cover.

  5. Hi all, I grew blue corn and my close neighbor grew sweet corn. We now both have a lot of ears with yellow and blue kernels. If I plant the blue kernels next year will I still get blue corn or will I get his hybrid? Thanks

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