Mid-ear cutworm injury resulting in subsequent ear mold infection by several pathogens. Image credit: G. Roth
In Pennsylvania and the surrounding region, growers often face challenges brought on by persistent moist conditions and other weather factors. One of these challenges include corn ear and stalk rots, and subsequent toxin contamination of grain and silage.
Our most prevalent ear rots in this region are Diplodia ear rot (caused by Stenocarpella maydis) and Gibberella ear rot (caused by Fusarium graminearum). Diplodia affects quality and yield, but Gibberella is the real concern for us as it can be associated with the production of a mycotoxin called deoxynivalenol (DON or vomitoxin). The fungus that causes Gibberella ear rot/stalk rot is the same fungus that causes scab in wheat and barley. And likewise, the DON issues that we fight in those crops can also be problematic in corn and corn byproducts. High levels of DON can show up not only in stored grain, but also in silage. Sometimes this problem may be compounded by farmers using dried distillers grains in the ration, since DON becomes more concentrated in the distilled byproduct. Another factor to consider is that straw used for bedding can also harbor DON if the wheat or barley crop it came from was affected by scab.
So while there are many sources of mycotoxins, here are some common questions regarding our most important mycotoxins in corn in Pennsylvania and the northeast.
Q. Will it be a bad year?
It depends. For Gibberella ear rot, the fungus enters through the silk, but can also get in through wounds made by insects or other sources of damage. Cool and wet conditions at the time of silking favor the sporulation of the fungus, and this means there will be more inoculum available to enter those silks. Then, once infection happens, a delayed harvest with lots of moisture enables the continued growth of the fungus. If these are your conditions, your risk of mycotoxin is higher.
The correct identification of the ear rots present in your fields is required to know if the type of ear mold there is an associated risk of mycotoxin contamination. For help with identifying ear molds there are plenty of resources available on the internet, including an app for that!
Q. Can fungicides help?
While a good deal of work has been done to examine using fungicides to reduce aflatoxins in corn, we do not have strong evidence for our more commonly encountered DON. Purdue plant pathologist, Kiersten Wise, released a paper in 2017 that showed while fungicides reduced the amount of ear rot in 2 out of 3 years, they did not reduce DON. The strobilurin products (which have been linked to increased DON), incidentally, did not increase the DON in this case, but it would still be wise to avoid stobilurin-containing fungicides if a crop is at high risk for mycotoxins. We need more research to determine if some of the newer chemistries will be able to reduce DON, but so far there is not enough evidence to make a strong recommendation.
Q. What do I do now with contaminated feed?
We recommend following the guidelines for testing and interpretation of test results for mycotoxins in feed .
Q. What should I do in the future to avoid this problem?
The best insurance against this issue is to invest in corn hybrids with some genetic resistance against these ear mold fungi. It may be a bit harder to find this information than for other attributes such as foliar disease resistance. This important knowledge can be disguised as “stalk strength” or “standability” in some cases as the fungi that cause ear rots are often the same as those that cause stalk rots. Corn with features that protect the grain inside the husk is critical, since any openings are a place where fungus can enter. Hybrids with downward turning tend not to let as much moisture enter the tip; those with husks that consistently cover the tip protect the grain from invaders; hybrids with insect resistance prevent feeding wounds that result in fungus invasion. Work with your seed sales representative to find a good hybrid that addresses these issues. It can make a world of difference!
As mentioned before, one of the ways fungi get into your grain is through feeding wounds. If you do not have suitable genetic traits to prevent insect feeding on your ears, you may want to consider an insecticide to protect the ears, specifically.
Work done at Cornell showed that in the Northeast, there is plenty of inoculum traveling in the air from field to field. This means that even if your field history doesn’t include susceptible crops like no till wheat and continuous corn, the fungus can blow in from any one of your neighbors’ fields. That said, the fungus does overwinter in residue of infected straw and stalks. So, baling off straw and fodder definitely won’t hurt in this situation, and adding some non-host crops into the rotation will help keep it from getting worse.