CLAY CENTER, NE--The stress from the summer's hot and dry conditions could mean the possibility of fungus--related corn diseases this fall, leading to harvest complications and reduced yields, University of Nebraska experts say.
One of the more common diseases to look for is stalk rot, a generic term for a whole variety of diseases, said Jim Stack, plant pathologist at NU's South Central Research and Extension Center here. The most common fungi, or molds, involved are Fusarium and Gibberella, which cause a reddish discoloration of the stalk. Several stalk rot diseases already have been diagnosed in central and northeast Nebraska this year, Stack said.
Stalk rot causes stalks to become so weakened that they easily fall over from wind, rain or snow. This makes corn ears on the stalks much more difficult to harvest. When stalks go down much grain gets left in the field, greatly reducing yields, the Institute of Agriculture and Natural Resources specialist said.
Stack suggests sampling a field for stalk rot by squeezing the lower third of 50 to 100 stalks to see if they compress easily. If one-fourth of the stalks collapse, that field is at a high risk of yield loss and should be harvested as soon as possible.
The fungi that cause stalk rot are everywhere and are well-adapted to dry conditions, Stack explained. Their populations "go wild" on stressed plants and under the right conditions can produce mycotoxins, toxic byproducts of mold growth. Mycotoxins can be harmful or even fatal to humans, livestock and wildlife when ingested. Molds can cause problems if breathed.
The presence of mold is not necessarily a problem, Stack said, but producers and elevator personnel should watch for molds as grain is stored this fall. Regardless of potential molds, individuals entering grain bins or elevators should always wear an appropriate nose mask to avoid breathing dust or molds.
Elevators routinely qualitatively test for mold growth and notify producers if disease is indicated. However, Stack said the black light test most elevators use frequently gives incorrect results because it reads things such as insect parts as the harmful compounds. The test is used because it is fast and inexpensive, he added.
A much more accurate test involves a chemical analysis, done by a laboratory. The NU Veterinary Diagnostic Center and commercial labs such as Midwest Laboratories in Omaha offer this service.
One black light test indicated positive for aflatoxin in some grain in southeast Nebraska this fall, Stack said. However, the chemical analyses later showed that grain to have only trace amounts, well below the 20 parts per billion allowance established by the federal Food and Drug Administration.
Specific chemical analyses can detect mycotoxins commonly found in grain. Aflatoxins infrequently are found in Nebraska, said Norm Schneider, NU veterinary toxicologist. They are more likely to occur in other parts of the Corn Belt and the southeast United States in corn and peanuts.
A potential bigger concern in Nebraska are mycotoxins produced by Fusarium, Schneider said, especially if wet harvest conditions develop this fall.
Nebraska Department of Agriculture inspectors are planning random sampling and testing throughout the harvest season, Schneider said. He and Stack will analyze the samples for additional common mycotoxins and fungi. If toxic compounds are found in harvested grain, it may be blended with unaffected grain, used for ethanol production, or fed to an animal species less sensitive to mycotoxins. Fattening steers and heifers usually can tolerate higher concentrations of mycotoxins in their diets, Schneider said. Dairy cows should never be fed aflatoxin--contaminated grain because of the potential for excretion in their milk.
If mycotoxins are found in lab--tested grain, producers will want to be wary of turning livestock out to graze stalks to clean up the corn left behind. If mycotoxins are present, determining whether to graze depends on which kind of toxins are present and its concentrations. Swine are more likely to be affected by Fusarium mycotoxins than cattle, he said, adding he would be more concerned about the potential for those mycotoxins than aflatoxin. In addition, nitrate can be a potential health hazard to livestock grazing drought--stressed corn.
Since the fungi that can cause stalk rot and other diseases are everywhere, Stack recommends producers manage their plantings and crops to reduce stress. One way is to select hybrid seed for stalk strength.