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mature cornstalks in Corn Watch 2019 field
NO STALK ROT: Stalk rot was not a factor in the Corn Watch ’19 field in mid-October. Dave Nanda says weather conditions weren’t favorable for stalk rot diseases then.

Expected stalk rot a no-show in early fall

Corn Watch: One key ingredient of the disease triangle was missing this season.

Rooting issues were a concern from the start in the Corn Watch ’19 field. It was planted May 28, and wet weather dominated most of June. In fact, beginning June 15, there were 10 straight days of rain. Soils were saturated, and young plants in a couple of low spots were under water briefly.

“We weren’t surprised when we found rooting issues by midseason,” says Dave Nanda, director of genetics for Seed Genetics-Direct, Jeffersonville, Ohio. Seed Genetics-Direct sponsors Corn Watch ’19.

Nanda inspected roots on a few plants and determined that they didn’t go as deep as normal. There were also compacted layers affecting rooting in places.

“There didn’t seem to be as many brace roots as usual,” Nanda says. “A few plants didn’t have any visible brace roots. We noticed some goose-necking of plants in a few spots. We determined it was due to rooting issues and not caused by rootworm feeding.”

Based on these observations, Nanda expected lodging problems with the crop as it matured. Because of the wet start and other stresses, he also expected stalk rot might come in early in this field, and many other fields planted into similar conditions.

Missing factor

A few plants were lodged during the last inspection of the field in mid-October, before harvest. But overall, the percentage of lodging was very low, and there was little stalk rot. In fact, Nanda searched to find an example of a stalk where stalk rot was evident.

Rooting issues and stress during the season usually set up plants for stalk rot. Why wasn’t it there? “It’s all about the disease triangle,” Nanda says. “To get a disease outbreak, you need three things: a susceptible host, the pathogen, and favorable environmental and weather conditions for the pathogen to flourish.

“We had the host — plants faced stress even though they produced good ears. The pathogen was present. You’re going to find ample amounts of fungi which cause stalk rots in almost any crop field because these pathogens overwinter in residue and survive in the soil.

“What we didn’t have was weather conditions favorable for the disease in September and most of October. Many areas were dry. Infection and spread of the disease are more likely when it’s moist and wet much of the time.”

It’s a classic example and a teachable moment, Nanda says. “The table was set for the disease, but favorable weather conditions didn’t exist early in the fall. All three parts of the disease triangle must be present for a disease to take off and cause damage. Take away the favorable environment, and the disease won’t develop, even though disease inoculum is present.”

That doesn’t mean stalk rots and lodging won’t become an issue for corn left in the field into late fall or beyond, Nanda cautions. Wet soils and late-fall storms with high winds can cause lodging. Whether stalk rots develop late depends upon whether moisture and temperature conditions favor disease.

TAGS: Crop Disease
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