Corn futures hit $4 and you decided to plant a few more acres to cash in on the biggest cash grain bonanza you’ve ever seen in a lifetime of farming.

You’d been thinking about it for a couple months, worrying about all of the changes in your cropping pattern, and calculating how to manage any additional production risk. One of those you risks you just thought about was the increased potential for fungus and other diseases carried from one corn crop to the next. You have some legitimate concerns.

However, those concerns can be managed according to University of Missouri plant pathologist Laura Sweet. In her December newsletter on Integrated Pest Management, Dr. Sweet says, “Diseases may cause leaf spots or leaf blights, wilts or premature death of plants. Corn diseases also can cause harvest losses, affect the quality of the harvested crop and cause storage losses.” In other words, there are plenty of gremlins that can quickly reduce the number of bushels you have to sell at $4 each.

Laura Sweet says pathogens can survive on 2006 corn residue and infect the 2007 crop with the help of weather, which she says has a significant impact on the severity of any disease. For categorical purposes, principal corn diseases can be divided into seed rots and seedling diseases; foliage disease; stalk and root rots; and ear and kernel rots. She says to minimize the impact of these yield killers, hybrid selection and agronomic practices become as important as weed and insect management.

Seed rot and seedling blight

You are already familiar with many types of fungus that can attack seedlings and cause seeds to rot, such as pythium, fusarium, rhizoctonia, which create perennial havoc in soybeans. They will thrive in cold, wet soil, so the soil environment at planting time needs to be your focus. To manage your risk:

1. Plant good quality seed of hybrids adapted for your area.
2. Plant under good seedbed conditions, especially at soil temperatures above 50 to 55 degrees F.
3. Use fungicide treated seed, which most commercial seed is, but you will want to control both water mold and other fungi, which may mean a multiple fungicide treatment.

Foliage disease

Once your crop is growing, it is susceptible to gray leaf spot, northern corn leaf blight, anthracnose leaf blight, yellow leaf blight, eyespot, and others. Fields infected one year produce spores the following year from launching pads on corn residue and are carried by the wind, either miles or inches. The only aliens are rust fungi, which will not overwinter, and need to be brought into the Cornbelt each year from the Gulf Coast, such as Asian soybean rust. Dr. Sweet says most of the foliar diseases in your corn field like wet, humid conditions, and heavy morning dew. If you’ve had foliage disease:

1. Select corn hybrids that are resistant to the diseases that you’ve had.
2. Rotate crops with at least one year out of corn, if possible, or do everything else possible.
3. Manage corn residues, but in reduced tillage systems, hybrid selection and crop rotation are especially important.
4. Follow appropriate fertility practices.
5. Manage insect and weed problems.
6. Plant at the proper population for the hybrid.
7. Apply foliar fungicides if warranted, particularly if you are producing an added value specialty crop.

Stalk rot

Stalk rots come from fungi and bacteria that live in the soil, in corn residue, or even in seed and survive from one year to the next. The pathogens may be blown onto leaves or stalks and they may enter stalks through corn borer holes or hail bruises. They may also infect the roots and grow upward unseen into the stalk. Stalk rots thrive when the plant is under stress from too much or too little water, temperature, cloudiness, hail, insects, nutrient deficiency and leaf disease. To manage risk of stalk rot:

1. Select hybrids with good stalk strength and lodging characteristics.
2. Plant at recommended populations for that hybrid.
3. Follow proper fertility practices.
4. Maintain good insect and weed control.
5. If irrigating, try to deliver optimum water from silking through late dough stage.
6. Avoid or minimize stress to corn (especially during pollination and grain fill).

Ear and kernel rot

These invade prior to harvest and can cause quality deterioration. These fungi may increase in prevalence with wet conditions after pollination and prior to harvest. They will survive either in the soil or in corn residue from the prior year. To manage your risk:

1. Select locally adapted hybrids with husks that close over ear tips.
2. Plant at recommended plant populations for that hybrid.
3. Maintain good plant vigor over the growing season.
4. Use a balanced fertility program.
5. Select planting dates appropriate for your area.
6. Follow recommended management practices to limit damage by ear-feeding insects.
7. If irrigating, try to deliver optimum water from silking through late dough stage.
8. Harvest in a timely fashion.

Summary:

While increasing corn acreage can potentially increase your revenue, it can also potentially increase your change of diseases left over from 2006. Seedling blights, leaf blights, stalk rots, and ear and kernel rots can seriously hurt yields, but can also be mitigated with a good risk management program. That stretches from selection of hybrids that are resistant to known diseases in your area, through good agronomic practices during the growing season, and ending with a timely harvest.

Stu Ellis

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