Identify Stalk Rot Before It Drops Your Yields

Charcoal rot is one disease to monitor if weather stays hot and dry.

Published on: Mar 4, 2013

Charcoal rot is among the corn diseases to watch out for in 2013 if heat and drought conditions continue.

Tamara Jackson-Ziems, UNL plant pathologist, says stalks weakened by stalk rot were evident in some corn in central and western Nebraska waiting to be harvested late last fall. High winds in October caused lodging of those weakened stalks.

Affected plants often have stalks that are hollow and easily crushed by hand or bent using either the "push or pinch" test. Stalk rot can occur at any point of the stalk, from the crown at or below the soil line all the way to the tassel. It's the stalk rot below the ear that causes lodging and losses during harvest.

STALK COMPARISON: These two cornstalks were split open to look for stalk rot disease. The one on the right shows discoloration caused by the disease charcoal rot and the one on the left that is healthier and less discolored. University of Nebraska-Lincoln photo
STALK COMPARISON: These two cornstalks were split open to look for stalk rot disease. The one on the right shows discoloration caused by the disease charcoal rot and the one on the left that is healthier and less discolored. University of Nebraska-Lincoln photo

Besides corn, charcoal rot can also affect other crops including sorghum and soybeans.

In corn, it's mostly likely to occur in dryland fields, including center pivot corners. "It thrives in hot and dry environments," she says.

Symptoms include numerous tiny black round structures inside the stalk, a condition that give the stalk a gray to black appearance. That's where the charcoal rot gets its name.

Jackson-Ziems recommends to walk through cornfields later in the season and randomly pick 100 plants, then push the tops to about a 30-degree angle. In this so-called push test, if the plant snaps back, it's okay, she says. "If the plants fail to snap back to vertical, then the stalk has been compromised by stalk rot." 

The pinch test works, too. "Pinch or squeeze the plants at one of the lowest internodes above the brace roots. If the stalks crush easily by hand, then their integrity is reduced by stalk rot and they are prone to lodging," she says. "If more than 10% of the plants exhibit stalk rot symptoms, then harvesting that field should be a priority over other fields that are at less risk.

~~~PAGE_BREAK_HERE~~~She also recommends using resistant hybrids.

Nothing can really be done once stock once stalk rot is identified in a field, she says. About the only management tip is to identify fields with the worst stalk rot disease and harvest them first.

In drought-damage fields, aspergillus ear rot can occur, as it did in some locations in2012. The fungal species that cause it can also produce aflatoxin, which can be toxic to livestock and even humans who consume contaminated grain.

"The vast majority of Nebraska's corn had safe levels of aflatoxin in 2012," she adds.

For more information on stalk rot diseases in corn, these UNL Extension publications can help:

•Corn Diseases Profiles II: Stalk Rot Diseases, at www.ianrpubs.edu/sendIt/ec1868.pdf
•Common Stalk Rot Diseases of Corn at www.ianrpubs.unl.edu/sendIt/ex1898.pfd
•CropWatch at cropwatch.unl.edu