Although western bean cutworm numbers were low this year, we have recently seen and also received reports about high corn earworm populations in late-planted corn and field peas. Corn earworm is a pest with many hosts including corn, tomatoes and certain legumes. In Ohio, it is typically considered a pest of sweet corn rather than field corn, but this past week substantial populations have been found in certain field corn sites in the northwest and northeast in late-planted fields. It is open to debate how well corn earworm can overwinter in most parts of Ohio, and the majority of our population probably immigrates each summer from more southern states. Dr. Celeste Welty, OSU vegetable entomologist, reports unusually heavy trap catches of corn earworm from early August through early September.
Corn earworms are damaging as caterpillars laid by moths on target plants. They vary quite a bit in color – with individuals that are dark brown, brown, tan, green, or even pinkish. Typically only one caterpillar is found per ear, but more may be found in heavy infestations. They enter corn ears at the tips where the majority of feeding occurs. This also opens the corn ear up to the potential development of ear rots. Chemical control of corn earworm in corn is virtually impossible once they have entered the ear, so at this point the scouting emphasis should be on assessing mold and disease levels in infested corn.
Feeding sites or exit holes when the caterpillar matures and leaves the ear leave holes in the corn husk, which provide a potential entry wound for pathogens like Fusarium and Gibberella. Some of these organisms can then be a further source for mycotoxins, including Fumonisins and deoxynivalenol, also known as vomitoxin. In some cases, damaged kernels will likely be colonized by opportunistic molds, meaning that the mold-causing fungi are just there because they gain easy access to the grain. However, in other cases, damaged ears may be colonized by fungi such as Fusarium, Gibberella and Aspergillus that produce harmful mycotoxins. Some molds that are associated with mycotoxins are easy to detect based on the color of the damaged areas. For instance reddish or pinkish molds are often cause by Gibberella zeae, a fungus know to be associated with several toxins, including vomitoxin. On the other hand, greenish molds may be caused by Aspergillus, which is known to be associated with aflatoxins, but not all green molds are caused by Aspergillus. The same can be said for whitish mold growth, some, but not all are caused by mycotoxin-producing fungi.
So, since it is not always easy to tell which mold is associated with which fungus or which fungus produces mycotoxins, the safe thing to do is to avoid feeding moldy grain to livestock. Mycotoxins are harmful to animals – some animals are more sensitive to vomitoxin while others are more sensitive to Fumonisins, but it is quite possible for multiple toxins to be present in those damaged ears. If you have damaged ears and moldy grain, get it tested for mycotoxins before feeding to livestock, and if you absolutely have to use moldy grain, make sure it does not make up more than the recommended limit for the toxin detected and the animal being fed. These links provides more information on ear molds and mycotoxin contamination and identification: