Expected stalk rot was ‘no show’ in early fall

Oct. 31, 2019

Rooting issues were a concern from the beginning 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 a few young plants in low spots were briefly under water.

“We weren’t surprised when we found rooting issues by mid-season,” noted Dave Nanda, Ph.D., director of genetics for Seed Genetics Direct.

Nanda inspected roots on a few plants and determined that they weren’t 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 said. “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 other fields planted into similar conditions.

However, while a few plants were lodged during the last inspection of the field in mid-October, overall, the percentage of lodging was very low and there was very little stalk rot. In fact, Nanda searched to find an example in which stalk rot was evident. Rooting issues and stress during the season usually forecasts for stalk rot. So, why wasn’t it there?

“It’s all about the disease triangle,” Nanda said. “To have 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; there will be ample amounts of fungi which cause stalk rots in almost any field because these pathogens overwinter in residue and survive in the soil.

“What we didn’t have was favorable weather conditions for the disease in September and most of October. Many areas were dry. Infection and spread of the disease is more likely when it’s moist and wet most of the time. 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 cautioned. Wet soils and late-fall storms with high winds can cause lodging. Whether stalk rots develop late depend upon whether or not moisture and temperature conditions favor disease.

The Corn Watch ’19 field is sponsored by Seed Genetics Direct. Reports on the field’s progress are provided all season (#CornWatch19); read the latest Corn Watch ’19 articles here.