Seed Rot Disease Of Corn: Reasons For Rotting Sweet Corn Seeds
By: Amy Grant
Sweet corn is rarely damaged by serious diseases in the home garden, especially when proper cultural practices are followed. However, even with the most vigilant cultural control, Mother Nature doesn’t always play by the rules and may have a hand in fostering seed rot in sweet corn. What causes rotting sweet corn seeds and what can be done to avoid seed rot disease of corn? Let’s learn more.
What is Sweet Corn Seed Rot?
Sweet corn seed rot is a fungal disease that can result from various species of fungi including but not limited to Pythium, Fusarium, Diplodia and Penicillium. All of these fungal pathogens affect the way the seed germinates, thus seedling development or lack thereof.
Infected tissue color reflects which type of pathogen has infected the seed. For example, white to pink tissue indicates the presence of Fusarium, bluish color indicates Penicillium while water-soaked striations indicate Pythium.
What Causes Rotting Sweet Corn Seeds?
Symptoms of seed rot disease in corn include decay and damping off. If seedlings are infected, they yellow, wilt and leaf drop occurs. Often, seeds fail to germinate at all and simply rot in the soil.
Seed rot in corn is most prevalent in soil with temperatures below 55 F. (13 C.). Cool, wet soil slows germination and increases the length of time the seed is exposed to fungi in the soil. Low quality seed also fosters weak seedlings that struggle or die in cold soil.
While the disease may attack less rapidly, warm soil will still encourage the disease. In warmer soil, seedlings may emerge, but with rotted root systems and stems.
Control of Seed Rot in Sweet Corn
In order to combat seed rot in sweet corn, use only high quality, certified fungicide treated seed. Also, plant sweet corn on a raised temperature and only after temperatures are consistently above 55 F. (13 C.).
Implement other cultural controls to reduce the chance of disease in corn:
- Plant only corn varieties suited to your area.
- Keep the garden free from weeds, which often harbor viruses, as well as insects that may act as vectors.
- Keep the plants regularly watered to avoid drought stress and keep them healthy.
- Remove smutted corn ears immediately and any corn debris post-harvest to reduce the incidence of diseases, resulting from corn smut and rust.
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Sweet Corn Seed Rot Disease - Tips For Controlling Seed Rot In Sweet Corn - garden
Having 8+ years of experience with growing field corn and a master’s degree in crop science, I thought I knew all there was to planting sweet corn however, my first time planting it was a flop. I planted the seeds as if I was raising 350 bushel field corn (who doesn’t want lots of sweet corn?) which resulted in lodged sweet corn plants. Come to find out you don’t plant sweet corn exactly the same as field corn.
Sweet corn is sweeter than field corn due to a “sugary (su) gene” sugary enhanced (se) and supersweet (sh2) varieties are also available, and to make the deal even sweeter, there are varieties with a combination of two and even three of the sugary genes synergistic (sy) and augmented supersweet (shA). Depending on your sweet tooth, you have some options for sweetness level.
When planting sweet corn, it should be planted in a block formation rather than a single, long row to allow for the plants to be closer together for adequate pollination. Without pollination, corn kernels will not develop on the ear. The recommended spacing for planting sweet corn is 8 to 12 inches apart in rows 2.5 to 3 feet apart with seeds being planted about 1 to 2 inches deep. Sweet corn does not tolerate cooler temperatures, so it is best to wait until soil temperatures have reached at least 60F (2 inch depth).
Corn is a nitrogen loving plant, so it is important to apply nitrogen for healthy growth. Ideally, it is best to apply nitrogen in split applications. A preplant application of a general-purpose fertilizer (10-10-10) can be applied at 25 lbs per 1000 sq ft. Sidedress recommendations vary and can be custom fitted to growing conditions. It is best to get the young plants off to a good start, so an additional nitrogen application is recommended when the plants are 6 to 12” tall apply 1 to 2 lbs of actual nitrogen per 100 feet of row. Spread fertilizer between the rows or on either side of a single row and lightly incorporate into the soil. It is recommended to make 2 to 3 sidedress applications throughout the growing season.
Sweet corn requires about 1 inch of water per week. Heat and moisture stress during pollination and grain fill can result in poor kernel set, so it is important to make sure plants get enough water during this time. During pollination, drip irrigation or soaker hoses are the best methods for providing additional moisture.
It is important to always start with a clean, weed free planting area. Once the corn is planted, light, shallow tillage can be done to control weeds between rows however, avoid getting too close to the root system of the plants. Mulching with grass clippings, straw, etc. can also be used to keep weeds down. Herbicides are also an option but be sure to read your label for proper application.
Corn earworm, European corn borer, corn rootworm, and Japanese beetles are the most common insect pests of sweet corn in the Midwest. Some sweet corn varieties have the Bt (Bacillus thuringiensis) protein to help protect against corn earworm and European corn borer. For varieties without the trait, Bt is also available as an insecticide spray for high insect pressure. Corn rootworm beetles and Japanese beetles can cause issues with pollination as they often feed on the corn silks. Other problematic insects of sweet corn include fall and common armyworm, corn flea beetle, black cutworm, and corn leaf aphid. It is always best to scout the crop periodically to check for the presence of insects and insect damage. Control is not necessarily warranted unless damage or insect numbers have reached a threshold. Threshold information for sweet corn insects can be found in the Sweet Corn Pest Identification and Management guide.
The diseases we see most often in sweet corn are Gray Leaf Spot (GLS) and Northern Corn Leaf Blight (NCLB). These two diseases overwinter on crop residue which is why we often see it every year. Crop rotation, tillage, and resistant varieties are the best management practices for these diseases. Common smut is often seen when plant tissue is wounded by hail, wind, or mechanical damage. Conditions that negatively affect pollination can also lead to the presence of smut. Anthracnose leaf blight and stalk rot as well as, crazy top and common rust are often seen in wet years as these diseases favor a moist environment. Southern rust can also be an issue in sweet corn however, it is only an issue when the pathogen is blown in from the south, and we have a hot, humid environment. Most of these diseases can be controlled through the use of resistant hybrids (if available), burial of crop residue, crop rotation, or application of fungicide. The Sweet Corn Pest Identification and Management guide is again a useful resource in identifying diseases and figuring out how to best manage them.
In addition to insects and disease issues, it is also common to face problems with vertebrate pests such as birds, raccoons, and deer. These can be a bit more difficult to control. The most common method of control includes electric fence to keep raccoons and deer out. To keep bird damage to a minimum, it is suggested to select varieties with tight husks or good tip cover. Typically, the earliest and latest ripening fields are subject to the greatest damage so try to plant at a similar time as neighbors. Repellents can be used for smaller home garden plantings but can be costly on a larger area basis. Repellents are most effective when coupled with other tactics such as electric fence to deter wildlife. If wildlife becomes too much of an issue, consult you state wildlife agency about the laws and regulations pertaining to shooting and trapping wildlife.
Depending on the variety, sweet corn can take 60 to 100 days to mature. By making successive 2 week plantings, sweet corn can be enjoyed for a longer period of time. Sweet corn should be harvested at the “milk stage” which is when the kernels are fully formed, but not completely mature. Once the silks dry out, start checking the firmness of the ear and the fullness of the tip kernels. Check frequently to make sure the ears do not become too mature. After picking, it is best to eat, can, or freeze the corn sooner rather than later, before the sugars decrease and starch content increases.
How To Prevent Common Sweet Corn Diseases
Know what to look for when it comes to corn diseases.
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.
Sweet Corn Diseases
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.
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.
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
This corn 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.
Like seed rot disease, this corn 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
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.
These insects 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.
Unfortunately, these 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.
These insects 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.
Along with 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.