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Outsmarting stalk rot

Most everyone knows a guy who provides the energy for any party. For most of the evening, he's cracking jokes and dancing with the charm and pep of a Hollywood leading man.

Funny thing, though. With little warning, the party animal often folds like a card table at the end of the evening.

That's the way the 2000 corn crop proceeded for many Midwestern farmers. For most of the season, good growing conditions made corn the life of the party. But in September, corn in many fields suddenly collapsed.

The culprit? Unlike the food and drink that fueled our party boy's demise, stalk rot was the villain that snapped the corn stalks.

The stalks just simply fell apart, says Dale Hicks, University of Minnesota extension agronomist. That happened after plants had reached maturity and filled out their kernels.

Damage was severe. For example, approximately 20 to 30% of the corn in Illinois had some degree of stalk breakage, says Emerson Nafziger, University of Illinois extension agronomist.

I've been in this business for 20 years, and there was never lodging as widespread as last year, adds Don Bockelman, corn breeder for Monsanto.

Pioneer Hi-Bred International research shows that the earlier lodging occurs, the higher the yield loss. Corn lodging in the soft dough stage can cut yields by 55%. Meanwhile, no yield loss occurs in black-layered corn. This research excludes downed corn that combines cannot harvest.

The stalk rot dilemma may have been averted if farmers had invested in hybrids with good stalk strength.

Why it happened. A combination of factors keyed last year's infestations. Three fungal diseases Gibberella, Diplodia and Colletotrichum (also known as anthracnose) cause stalk rot. All three organisms reduce corn yield by killing the plant before grain physiological maturity occurs.

These agents overwinter in residue and produce spores when the weather warms in the spring. Warm temperatures and high humidity favor infection later in the year.

That's what occurred last September in parts of Minnesota. Last year, plants matured earlier than normal due to early planting dates, Hicks says. A hot Labor Day weekend simply cooked the plants because they ran short of moisture. Then we moved into a time period where average air temperatures were higher than normal, and that facilitated the growth of stalk rot organisms.

The increase in conservation tillage across the Midwest has also helped spur stalk rot outbreaks, says Lonne Fry, area agronomist for the Garst Seed Company, La Harpe, IL. The resulting residue provides safe haven for stalk organisms to develop.

We're creating a wonderful environment for these diseases when the right kind of weather conditions causes them to explode, Fry says.

Stalk rot also can occur even when plants resist these microbes. Environmental stressors, such as cloudy skies, can curb plant photosynthesis, which is the process by which plants convert sunlight into nutrients such as carbohydrates and sugar. When environmental conditions limit photosynthesis, plants must turn inward to sustain themselves.

This stresses two stalk components: the inner soft pithy tissue and the hard outer rind. The pithy tissue is rich in sugars and other nutrients, says Bill Dolezal, research coordinator for pathology and entomology for Pioneer.

During the grain-filling phase, competition within the plant for nutrients is intense. If photosynthesis permits the plant to garner nutrients, it can fill grain and still support itself. But if environmental stressors curb photosynthesis, the plant will tap the pithy tissue for sugar. Supported just by the rind, the plant often collapses.

In these cases, the plant shuts down and cannibalizes itself, Hicks says.

The situation worsens in years, like last year, with high yield potential, Dolezal says. There was a tremendous commitment of corn plants to fill grain all the way out to the end of the ear. But there were a lot of cloudy or highly overcast days when we didn't get enough photosynthesis production.

Drought also can induce stalk rot. Dry weather during July and August helped key much stalk rot in Illinois, Nafziger says. We had plants that were really charged up to produce a lot of yield, and stalk strength was sacrificed in pursuit of yield, he explains. Stalk rot was very hybrid specific in a year in which some pretty good hybrids came up on the short end. Farmers were able to harvest fields, but it was a very painful process.

What can you do? No one suggests that farmers shelve conservation tillage and bring back the moldboard plow. The soil-saving attributes of conservation tillage far outweigh the disadvantage of disease-harboring residue.

Some farmers will moldboard plow this year to minimize disease pressure, Fry says. However, that's a futile effort because wind can spread stalk rot organisms.

Nor can you control weather conditions that fuel stalk rot. However, you can reduce stalk rot potential by buying resistant hybrids with good stalk strength.

Unfortunately, hybrids with high stalk rot resistance often aren't the top-yielding ones. This creates an offense and defense game that rivals any Super Bowl matchup.

Dolezal says that all Pioneer hybrids have some base-level resistance to stalk rot. Yet defensive hybrids have more resistance than offensive hybrids.

Generally, the more defensive hybrids to stalk rot aren't as offensive on yield potential, Dolezal says. Last year would have been a good year to have a more defensive hybrid. Hybrids that were very offensive got into trouble last year.

The increase in conservation tillage has helped spur stalk rot outbreaks. We're creating a wonderful environment for these diseases when the right kind of weather conditions causes them to explode.
Lonne Fry, area agronomist
Garst Seed Company

In a normal year, though, offensive hybrids yield more than defensive hybrids. You cannot predict which year that will be, Dolezal says.

Thus, it's best to target resistant hybrids to areas with chronic stalk rot problems, says Wayne Fithian, agronomy systems manager for The J.C. Robinson Seed Company/Golden Harvest.

If you have fields that are relatively easy to manage, it's probably less of a concern, Fithian adds.

Check the ratings. You can obtain information on stalk strength and stalk rot resistance from ratings that companies assign to their hybrids. Dolezal recommends that, before you buy hybrids based on these ratings, know which culprit caused your corn to crash. For example, a hybrid's resistance to Gibberella may be stronger than its resistance to anthracnose. If anthracnose caused the stalk rot, Gibberella resistance will be useless.

In other cases, stalk rot may be related to weather conditions. Thus, good stalk strength would be the best safeguard against lodging.

Bear in mind that ratings can be enigmatic, because stalk rot susceptibility can vary widely among hybrids between years.

In addition, ratings assigned to hybrids by different companies can be difficult to compare. No universal rating system between companies exists, Fry says. This makes it very confusing for farmers who use these as a selection guide. He advises producers to garner information from a variety of sources, such as seed company ratings, local performance reports and independent testing groups.

The best way to reduce stalk rot risk is to plant a wide mix of hybrids, says Steve Sodeman, a Trimont, MN, crop consultant. Farmers should plant a hybrid on no more than 10% of their acres, he adds. It's just like a baseball team. You'll always have some bum players. Planting a variety of hybrids is a way to decrease the chances of planting a susceptible hybrid.

That's sometimes easier said than done. The things that force farmers to choose fewer hybrids are these stupid volume discounting systems, Sodeman says. If you just a plant a couple hybrids from one company, you'll get a big discount. But that can set you up for problems if one of those hybrids goes down.

Fungicides also can curb stalk rot infections, but drawbacks exist.

The bad part of using the fungicide is that it's more of a preventive measure than a corrective measure, Fry says. Fungicides only protect corn against fungal outbreaks for a two-week period. Plus, heavy rainfall during this time can literally wash away the $16 to $17/acre cost.

Other ways to snap stalk rot. If your cornfields have a history of stalk rot, here are some other ways to curtail its effect.

  • Avoid high nitrogen levels.

    This vital nutrient powers a plant's yield. However, excessive N levels accompanied by low potassium levels can compound stalk rot. Potassium promotes strong stalk development. Low K levels can increase stalk breakage if high N levels spur rapid growth, Dolezal says.

  • Manage insects.

    If you control corn rootworm and European corn borer, this will also help reduce incidence of stalk rot by preventing entry points for disease-causing organisms, Fithian says.

  • Prioritize harvest.

    In years of stalk rot infestations, we advise growers to leave the fields planted to hybrids with the best stalk strength ratings until last, Fithian says.

  • Reduce crop stress.

    It's impossible to totally eliminate crop stress, Dolezal says. However, good management can reduce it. Excessive plant populations will increase stress and stalk lodging. Poorly spaced or clumped plants create a high population microenvironment similar to over-planting. Maintain planter meters properly, and do not exceed the manufacturer's suggested ground speed. Carefully calibrate planter meters for optimum plant spacing and monitor rates when planting.

  • Use special combine reels to harvest downed corn.

    If stalk rot flattens your corn, fit your combine with a special reel. Even though stalk breakage tallied 20 to 30% in some areas of Illinois, Nafziger doesn't think losses were high in most fields, because farmers used special reels for harvest.

The best way to reduce stalk rot risk is to plant a wide mix of hybrids. Farmers should plant a hybrid on no more than 10% of their acres. It's just like a baseball team. You'll always have some bum players. Planting a variety of hybrids is a way to decrease the chances of planting a susceptible hybrid.
Steve Sodeman, crop consultant
Trimont, MN

Units include the Kelderman reel, which moves corn off the header and into the combine. Without the reel, the operator would need to repeatedly stop to clear the corn head of stalks and ears. A six-row kit costs $1,876; and an eight-row kit costs $2,125. For more information, contact Kelderman Equip., Dept. FIN, 2686 Hwy. 92 E., Oskaloosa, IA 52577, 800/334-6150, or circle 203.

The Meteer corn reel is similar to the Kelderman reel. Its revolving fingers help feed lodged corn into the head. Depending on your combine size, kit cost ranges from $850 to $1,525. You'll also need a $435 motor. For more information, contact Meteer Mfg., Dept. FIN, RR 1, Box 221, Athens, IL 62613, 217/636-8109, or circle 204.

Roll-A-Cone Manufacturing has two different types of plastic cone attachments, one for a cone head and another for a soybean-type head. The kits cost about $425 per combine row. For more information, contact Roll-A-Cone Mfg., Dept. FIN, Rt. 2, Box 25, Tulia, TX 79088, 806/668-4722, or circle 205.

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