Vomitoxin in Corn

 

As harvest progresses, farmers are finding vomitoxin in their corn. Gibberella (GIB) ear rot is caused by Fusarium graminearum, a fungus that is also called Gibberella zeae. This pathogen infects corn and wheat causing ear rot, stalk rot, and head scab. Corn symptoms include a reddish or pinkish-white mold on the ear tips. This pathogen infects the pollen tubes at pollination and then produces vomitoxin and other toxins as it grows. The pathogen over-winters on plant residue, usually corn stalks/leaves and wheat residue (straw and chaff).

GIB ear rot is most prevalent when cool wet weather occurs for about 21 days after silking. Fields most susceptible are corn after corn or corn after wheat, especially if the wheat was infected with Fusarium head scab. Corn that is stressed from lack of nutrients, by insects, or other types of plant stress (soil compaction, poor soil health) tend to have higher levels of GIB ear rot.

Nutrient stress may come from nitrogen (N), phosphorus (P), and potassium (K) imbalances. High N with low K is often associated with higher levels of GIB ear rot. Nitrogen fertilization in the form of ammonia and adequate levels of P may decrease GIB ear rot. In corn, about 50% of P is absorbed by plant roots after plants start the reproductive phase. Another element that helps reduce GIB ear rot is chlorine (Cl). A good source of fertilizer is potassium chloride (KCL) to help fight this pathogen. The Cl also makes manganese more plant available to help the plant fight the pathogen (Mineral Nutrition and Plant Disease, 2018).

In GIB ear rot, zinc is a mixed bag. Wheat that is zinc deficient seems to have higher incidence of Fusarium wheat scab. Zinc fertilization in wheat helps plants suppress Fusarium, Rhizoctonia, and take-all diseases. However, in corn, high levels of zinc seem to be associated with more GIB ear rot. The fusarium needs zinc to make the toxin. Sometimes the corn plant is zinc deficient but the fusarium is high in zinc. Perhaps the fusarium pathogen is stealing the zinc from the corn? More research is needed to understand the importance of zinc with GIB ear rot.

To reduce GIB ear rot before it occurs, there are several things to consider. Good crop rotation is the first step. Avoid planting corn or wheat after fields that show signs of this infection. Good soil health and fast residue decay are needed to reduce level of the pathogen. Ideally, at least 80% of your residue (wheat or corn) should be decayed by planting time. Crop residue decay is dependent upon adequate soil moisture, soil temperature (above 500F), adequate microbial activity (mycorrhizae fungus for lignin breakdown), and good macrofauna (springtails, mites, earthworms, etc.) that breakdown the crop residue into smaller pieces. Overuse of soil insecticides may reduce crop residue decay.

Farmers can select crop varieties that are somewhat resistant to GIB ear rot. Earlier maturing corn varieties have more time for crop residue to break down in the fall. Also, planting a cover crop, not only improves soil health and increases beneficial soil microbes, it also creates a microenvironment (warmer, higher moisture) where crop residues may decay faster. Cover crops also reduce soil compaction and may help balance soil nutrients (N-P-K-Cl).

Here are some corn harvesting tips from Purdue Extension. Harvest high GIB ear rot corn fields separately and as quickly as possible. Fines and smalls hold more GIB ear rot pathogen, so adjust the combine to reduce this source of infection. Grain moisture above 22% moisture and 800F increases mold developments, with cooler temperatures and lower moisture decreasing the spread. In field, moisture levels below 18% stop mold development.

Here are some grain storage tips from OSU Extension (Dr. Paul Pierce). 1) Dry harvested grain to 15% moisture and below to prevent further mold development in storage. 2) Store dried grain at cool temperatures (36 to 440 F) in clean, dry bins. Moderate to high temperatures are favorable for fungal growth and toxin production. 3) Periodically check grain for mold, insects, and temperature, and send grain samples for mycotoxin analysis. 4) Avoid storing severely affected grain for too long especially since it becomes much more difficult to keep grain cool and dry as outside temperatures increase in the spring and summer.

For feeding grain, swine (hogs) are the most susceptible followed by poultry. Ruminant animals (beef cattle and dairy) can tolerate slightly higher levels of vomitoxin or Deoxynivalenol (DON). For swine, 5 ppm DON is the maximum feed level allowed, for poultry 10 ppm and dairy cattle 10 ppm. Animals may refuse the feed or vomit and DON may cause abortions and infertility in breeding animals.