Some farmers in west central Minnesota harvested corn early this year, sacrificing $5-10/acre from the bottom line due to higher drying costs. The culprit: corn stalk rot.
“We've had a lot of downed fields here,” says Craig Bulau, an agronomist at Consumers' Co-op in Litchfield, MN. “I'd estimate that 30% of fields were affected in our area.”
It was a similar story in other parts of the Corn Belt where hot, dry weather set the stage for widespread corn stalk rot diseases. As always, stalk rot incidence varied from region to region, says Don White, a plant pathologist from the University of Illinois. But in many areas of the Corn Belt, environmental conditions favored the fungal diseases, which tended to appear “anywhere you had drought and heat stress together.”
Stressed corn plants can't make enough carbohydrates to fill kernels and also maintain healthy roots and stalks. In these circumstances, “the ear takes priority,” White explains, leaving the rest of the plant short of nutrients. The weakened tissues are susceptible to infection by opportunistic fungi that live in corn debris and soil.
Stalk rot pathogens common throughout the Corn Belt include giberella, colletotrichum (anthracnose) and fusarium, says Dean Malvick, a plant pathologist from the University of Minnesota. Diplodia and corn charcoal rot are more common south of Minnesota and Wisconsin.
These pathogens cause internal stalk tissue to decay. Infected plants may die prematurely, shutting off grain production. But more often, Malvick says, plants lodge easily, making the field difficult to harvest.
Stalk rot diseases are usually associated with mid- and late-season drought. West central Minnesota, for example, was very wet early in the growing season, then hot and dry from mid-July through August, says Jason Fussy, an agronomist with Centrol, Inc., a crop consulting firm. Temperatures frequently climbed above 90°.
Other environmental conditions that foster stalk rot include excess moisture in the spring, hail, wind and insect feeding. “High yields can be a stress, too,” says Bruce Potter, an IPM specialist with the Minnesota Extension Service. “Bigger-eared plants have more stalk rot problems.”
There's no treatment for stalk rot. If 10-15% of plants in a field are infected, early harvest should be considered, Malvick says. However, growers must weigh the potential for losses from stalk breakage against higher drying costs.
Stalk rot is tough to manage. “There are certain things we see every year, and stalk rot is one of them,” Potter says. Farmers should try to minimize plant stress as much as possible.
Crop consultant Steve Commerford, of Commerford Agronomics in New Ulm, MN, advises against planting corn on corn. Growers should control corn borers and corn rootworms, avoid applying excess nitrogen, “and make sure potassium fertilizer or soil fertility is adequate,” he says.
It's also important to look for hybrids that show stalk rot resistance and good standability. In fields with a history of stalk rot, it may help to plant longer-maturity hybrids, Commerford says.
In addition, “Growers shouldn't exceed recommended plant populations,” says White, the Illinois plant pathologist. Over-populating fields puts more stress on the corn plants.
White says growers may complain more about stalk rot these days “because there's a tendency to leave the crop in the field longer, so there's more chance for plants to fall down.” In fact, he says, “There's been a phenomenal increase in stalk rot resistance since the 1960s.” But as plant populations and yields push up, “We're placing a lot of stress on plants, so we're always on the edge of stalk rot problems.”
(Editor's Note: The University of Illinois has published an illustrated pocket guide to common corn diseases, “Field Guide to Corn Diseases,” by Don White, Dean Malvick and Aaron Hager. To purchase a copy, contact the Department of Crop Sciences at the University of Illinois at Urbana-Champaign, or e-mail Dean Malvick at dmalvick@umn.edu.)