Corn producers in western and west-southwestern Illinois should be on the lookout for symptoms of Diplodia ear mold during harvest. An informal survey of several grain elevators and farmers in Western Illinois reported up to fifty percent kernel damage in some locations. Factors such as planting date, the timing of rain events after fertilization, and hybrid susceptibility can result in a range of damage within the larger region and even within a farming operation, according to University of Illinois Extension educator Angie Peltier.
"Diplodia ear mold can cause lightweight kernels with a dull grey to brownish color and sometimes small black fruiting structures call pycnidia," Peltier says. Infected kernels are prone to breakage and can result in poor test weights, poor grain quality, and fine materials in the hopper or grain bin. Peltier recommends adjusting combine settings to maximize grain cleaning and minimize breakage.
Elevator and ethanol facility personnel suggest that the threshold for accepting damaged grain can vary depending upon the local market and end-use. The price at which a farmer can market grain begins to decrease for every percentage point of damaged kernels above five percent.
"Some grain elevators will set a damage threshold above which they will not accept the grain. I have heard anywhere from above 15 to 50 percent damage, depending upon the end use and how quickly the grain will leave the elevator," Peltier says.
Stenocarpella maydis, the fungus that causes Diplodia ear mold, metabolizes the starches in corn kernels leaving them lighter weight than non-infected kernels. The ethanol manufacturing process uses bacteria to turn corn starch into simple sugars, eventually fermenting them to yield ethanol. Diplodia-damaged kernels can yield less ethanol and may explain why elevators that supply ethanol plants may have a lower threshold for damaged kernels than others.
One positive is that unlike Aspergillus, Fusarium, or Gibberella ear molds, Diplodia ear mold is not associated with a mycotoxin. Regardless of whether infected kernels are in the field, in the combine hopper, semi-trailer, or grain bin, the fungus will continue to grow and metabolize starches unless the grain is cooled and dried to below 15 percent moisture. Unless properly dried, the fungus can colonize uninfected kernels that are damaged during harvest or storage operations.
With on-farm storage, many crop producers have the option to hold onto their grain to market it at a later time.
"I recommend storing diseased grain separately and for only short periods of time to reduce the chance of additional losses," Peltier says.
It is important for producers that encounter Diplodia ear mold to be in communication with their crop insurance agent. While the high yields expected this year may offset lower grain prices overall, those farmers with low sale prices due to a lot of dockage may be able to recoup some of their losses.