Stopping Ear Rot

Barbara Prater
May 01, 2002

Gretchen Kuldau keeps a decorative ear of corn in her office. The kernels are a deep purple hue tinted with brown; the husks have been pulled over the end of the cob and arranged in pleasing layers. The ear doesn't hang on the wall for decoration, though; it sits on a shelf in a plastic bag, demonstrating what Kuldau calls a "good example of ear rot." A closer look reveals an imperfection, a blotch of white fuzz with a rotted kernel in the center.

three ears of corn tied together
Bill Schimio

Ear rot is caused by fungi. Some of these fungi produce mycotoxins, poisons that can be an expensive problem for farmers. Mycotoxins wreak havoc on the bodies of livestock who eat infected feed corn. They can cause "hole in the head" disease in horses, which turns the white matter of their brains to liquid. They can add estrogen to an animal's system, causing reproductive problems in females and feminization in males. Some animals, "especially pigs," says Kuldau, "won't eat food with the toxin in it. We're not sure if they smell it, or if they start to eat it and get sick, but they will sometimes avoid it or nudge it out of their food."

Insects, such as the European corn borer, compound the problem. When they bore into an ear of corn, they create an opening in the "skin" of the kernel. "Much like when we cut our hand and bacteria gets into it," explains Kuldau, "insects create a pathway for infection." In addition, insects may give fungus a piggyback ride as they pierce an ear, not only creating a pathway but also becoming a vector, or carrier, of the disease. The decorative ear of corn in Kuldau's office confirms this method of infection; visible on the dried husk, lining up perfectly with the center of the infected kernels, is a small hole created by a bug.

Corn can be genetically engineered to resist the bugs that bring fungus into the ear. "Bt corn," for example, produces a toxin from the bacterium Bacillus thuringensis that kills the European corn borer. By eliminating the corn borer, in theory fewer pathways will be introduced into the kernels of corn and fewer will be infected with mycotoxins. Because the genetically modified seeds are patented, though, they are more expensive.

The cost effectiveness of Bt corn is the focus of one of Kuldau's research studies, led by entomologist Dennis Calvin and in conjunction with agricultural economist Jeffrey Hyde, agronomist Gregory Roth, regional extension agent Del Voight, and collaborators from the University of Maryland and Cornell. Kuldau's role is to check ears of corn for ear rot and then to analyze the infected ears for mycotoxins. The group is investigating five different brands; for each, they are examining both the Bt corn line and the same line without the Bt gene. Field sites were spread throughout Pennsylvania and Maryland in order to reduce the impact of local weather, and were divided into plots based on which type of seed had been planted.

From each plot, Kuldau received a bag of 20 ears to examine, totaling over 3,000 ears. She was not told if the ears in each bag were Bt corn or not. She examined each ear for the characteristics of a fungal infection, and then noted "the percent of kernels infected with fungus on each ear," devising a rating system based on the coverage of fungus.

After the lines of corn were revealed to her, Kuldau was able to analyze the degree of infection for each line. In her preliminary analysis, corn from plots near Hershey, Pennsylvania, had a much lower rate of infected ears in the Bt corn lines than in the non-Bt lines. The rate of infected kernels, however, is also important, and she is still examining the results to compare the lines. Also, to complete her study, she must analyze the infected ears for their concentration of mycotoxins, since, says Kuldau, "the amount of fungus and the concentration of mycotoxins are not always correlated."

The Bt corn study will assist farmers in balancing many factors when choosing their corn seed—cost, yield of corn, and amount of ear rot and mycotoxins present. So far, says Kuldau, "The farmers seem to like the product enough to go ahead and pay the premium price for it and plant it." They will accept a higher cost for seed in order to save money in yield and in livestock health down the road.

Gretchen A. Kuldau, Ph.D., is an assistant professor of plant pathology in the College of Agricultural Sciences, 205 Buckhout Lab, University Park, PA 16802; 814-863-7232; Gregory Roth, Ph.D., is an associate professor of agronomy; Dennis Calvin, Ph.D., is a professor of entomology; and Jeffrey Hyde, Ph.D., is an assistant professor of agricultural economics; and Del Voight is regional extension agent, all in the College of Agricultural Sciences. The Bt corn study is funded by a grant from the United States Department of Agriculture Northeast Integrated Pest Management.

Last Updated May 01, 2002