Discussions and experiences related to vomitoxin, which is also referred to as DON, in corn silage continues to perplex both livestock producers and researchers. Although there are more potent mycotoxins than DON, none are more common in regions of the U.S. where corn silage is widely grown.
“Mycotoxins are secondary metabolites produced by fungi that can be toxic to plants and animals,” says Damon Smith, University of Wisconsin extension plant pathologist. “These are termed secondary metabolites as they are not produced by primary metabolism in fungi. We understand some things about secondary metabolism in fungi, but there is much left to learn,” he writes in his Badger CropDoc blog.
In corn, DON is produced primarily by a fungus called Fusarium graminearum, which is responsible for Gibberella ear rot and also Gibberella stalk or crown rot of corn.
Smith is on a mission to find some answers. During the past two growing seasons, he and his co-workers have designed and completed several field trials to see if fungicide applications effect DON concentration levels and determine if DON is preferentially accumulating in certain plant parts. In a summary of his research to date, Smith cites the following results to date:
1. DON can accumulate in both corn ears and stalks.
2. Some hybrids might be more susceptible to stalk DON accumulation than ear DON accumulation. In one trial, comparing two different hybrids, DON was higher in the ears of one and the stalks of the other.
3. DON accumulation in stalks looks to be independent from ear DON accumulation.
4. Fungicide applications may not always reduce DON, especially in years conducive for F. graminearum or when stalk infection is a primary means of DON accumulation in the corn plant. Smith notes that it might be hard to get fungicide into stalks to reduce stalk infection. Thus, DON still accumulates in the stalk portion, independent of ear infection control by fungicide applied at the R1 (silking) stage.
5. The best all-around fungicide timing when trying to reduce DON is still at R1, though this may differ depending on the product used. Smith says that this timing has the best chance of reducing DON in the ear, where DON concentrations can be high in some hybrids. He thinks earlier applications at V6 could be reducing stalk infection and subsequent DON accumulation in stalks, but more work needs to be done to confirm this.