Fumonisin, found in corn last fall across the Texas High Plains, caused a lot of concern among farmers. Incidences of fumonisin were higher than usual because of hot, dry weather during corn silking and grain fill, followed by cool, rainy weather near harvest.
Fumonisin is a group of mycotoxins produced by fungi, primarily Fusarium verticillioides and Fusarium proliferatum. Fusarium verticilliodes is a common pathogen in corn and is found everywhere the crop is grown.
Fumonisins are more prevalent in corn, but sometimes occur in other cereal crops as well. The mycotoxins concentrate in corn kernels, so they are a concern when the grain is fed directly or mixed in silage or other feeds.
“Poultry and cattle are not especially susceptible to fumonisins,” says Steve Koenning, Ph.D., plant pathology extension specialist at North Carolina State University. “In horses, however, they cause a serious disease called equine leukoencephalomalacia (ELEM). Fumonisins are responsible for porcine edema, a swine disease, and is a possible cause of human esophageal cancer. The mycotoxins are also a risk to rabbits and catfish.”
FDA guidelines for fumonisins in animal feed are shown in Table 1 and provide an indication of the degree of susceptibility of various animals.
“Although fumonisin toxin is produced by certain species of fusarium fungus, not all kernels infected with these fungi will contain the mycotoxin. Chemical analysis is required for determining fumonisin content in grain,” says Tom Isakeit, plant pathologist with Texas A&M AgriLife Extension.
“Although the toxin doesn’t produce visible signs, one of the symptoms of the fungal infection is white streaks on kernels. These white streaks are visible fungal growth and are called the ‘star burst’ symptom. After infected kernels are dried, they become smaller and lighter than the healthy kernels.”
“The disease is called fusarium ear rot, and other symptoms can include kernels that appear tan or brown,” says Charles Woloshuk, Ph.D., Purdue Extension. “In corn ear rot, fusarium-diseased kernels are isolated or occur in patches on the ear.”
“Fumonisin occurs in both dryland and irrigated, and short-season to full-season corn,” says Wenwei Xu, Ph.D., Texas A&M AgriLife Research. “Contamination varies from field to field, and the severity is determined by the hybrid, plant growth management, temperature and amount of drought stress on the crop.”
Harvest management of an infected crop
“Scout fields at kernel maturity to determine presence and severity of fusarium ear rot,” Woloshuk says. “Harvest infected areas first, because leaving affected grain in the field increases risk of fumonisin contamination.”
“There are certain best management practices to use when harvesting a field infected with fumonisin,” says Isakeit. “One recommended practice is to adjust combine settings to discharge smaller grain kernels, because they tend to have the higher concentrations of fumonisin.
“Severity of the mycotoxin is sometimes lessened by cleaning seed or removing damaged kernels. A few contaminated kernels can cause a high concentration in a load of corn. Artificially drying corn from a high moisture content like 24 percent to 15 percent in a 24-hour period can also minimize contamination. Moisture levels between 18 and 20 percent are ideal for fumonisin production. At 17 percent or less grain moisture, fungal growth and fumonisin production normally cease.”
Producers should harvest moisture-stressed areas of the field separate from the rest, and keep the two collections segmented during handling and storage. The worst fumonisin contamination usually occurs around field edges.
“Putting corn into storage won’t rid it of fumonisin,” Isakeit warns. “High levels of moisture or water leakage in bins adds to the problem. Store corn dry and keep it dry. Make sure bins are operated properly and are well-ventilated.”
Protect future crops
Very few foliar fungicides have been labeled for fusarium ear rot and for those that have, continued efficacy has not been demonstrated. Research has shown, however, that controlling insects such as earworms and European corn borer significantly reduces impact of fusarium ear rot disease. Insect resistance, including that in transgenic hybrids, can help prevent fumonisin contamination by reducing wounds in the kernels that allow entry of fusarium fungus.
“The best methods to prevent severe ear rots and high risk of fumonisin contamination are selection of the right hybrids and use of proper cultural practices,” says Xu.
“There is a clear distinction in fusarium infections among hybrids. Resistance to fusarium fungus disease, common smut and earworm damage should play a large role in hybrid variety selection. Susceptibility to these threats doesn’t mean that every field will be severely affected by fumonisin, but when environmental conditions are right for kernel damage, toxin contamination can become elevated.”
“Common smut disease also plays a role in fumonisin contamination of corn,” Xu says. “Smut acts as a sponge and retains moisture in the ear, allowing fusarium to grow and produce the toxin. Corn ears that remain standing at maturity instead of falling also retain moisture.”
Cultural practices that help reduce fumonisin contamination include weed control. Weeds rob moisture from the soil, making it unavailable to corn. This causes moisture stress on the crop, creating an environment for toxin infestation.
Good irrigation management is important for reducing fumonisin contamination. Optimize timing and amount of irrigation between flowering and grain fill to prevent plant stress. Proper nitrogen fertility also reduces stress, particularly in high-plant populations.
It is difficult to prevent fumonisin contamination of corn when conducive environmental conditions occur; however, selecting the right crop hybrid and using good cultural practices reduces severity. 
PHOTO: You may not be able to eradicate fumonisin, but you can use best management practices to contain it. Photo by Mike Dixon.
Robert Fears is a freelance writer based in Georgetown, Texas. Email Robert Fears.
