Fusarium head blight in oats

Fusarium head blight in oat.
Photo: Jafar Razzaghian (NIBIO)

Yes, that is correct. Generally, when we hear about Fusarium head blight (scab) issues or risk of scab and management decisions to be considered, we are talking about spring wheat and barley. Summer 2024, concerns in spring barley and wheat were certainly the case, but fast forward to fall of 2024 and spring wheat and barley were not the only crops with issues. Significant infections had occurred in oats and contamination of harvested grain was a concern.

Fusarium head blight (scab) is caused by several fungal species in the Fusarium genus and is of particular importance because the disease can contaminate harvested grain with deoxynivalenol (DON). DON, a vomitoxin, is an important mycotoxin that can negatively impact human and livestock health.

The Food and Drug Administration (FDA) recommends a 1 part per million (ppm) DON tolerance in oats to be milled for human consumption. FDA also recommends that DON concentrations in grains and grain byproducts for livestock should not exceed 5 ppm, but tolerable levels of DON will vary by livestock species and age. Swine are particularly sensitive while other livestock species will vary in their tolerance. It is best to test harvested grain to determine acceptable uses for the grain. There are several commercial laboratories in the region that can test for the presence of DON in grain, including Midwest Laboratories, South Dakota Agricultural Labs, and Minnesota Valley Testing Laboratories.

Managing scab risk in oats with fungicide is not well understood and infections are difficult to detect and assess in the field. So, in years where we see significant scab in oats, we will need to also look to post harvest management to reduce the concentration of DON in the harvested grain. The first step is to test samples for DON to determine a suitable use for the grain or to determine how to blend grain to decrease DON concentrations to acceptable levels for the desired use. Testing for DON is challenging as was explained in an August 21 Crop News Article, Small grains harvest progress report: DON and HFN. In some circumstances grain originally grown for human consumption might not be marketable as such, due to the grain’s DON concentration being too high to blend down to acceptable levels.

What else should be considered?  In Fall 2024, we met with a group of farmers in southeast Minnesota, to look at post-harvest grain cleaning options to decrease DON levels, something that works reasonable well in wheat.  Farmers brought in oat grain samples from their bins, and we tested two methods of grain cleaning.  Samples were either cleaned with a tabletop aspirator or tabletop AT Ferrell Clipper seed cleaner at varying levels of cleanout.  Percent cleanout was evaluated along with the effect on DON concentration.  Unfortunately, the results were not very promising for post-harvest management of DON concentration in oats via grain cleaning.

 Table 1. Grain samples varied in their DON concentration from 1.1 to 7.7 ppm.

Lot	DON (ppm)
1	2.2
2	9.4
3	6.5
4	3.5
5	6.4
6	5.5
7	7.9
8	6.3
9	2.2
10	1.0
11	1.5

Samples varied in their DON concentration and lots 1, 4, 10, 11 and 6 would likely be marketable to millers and elevators when DON is measured on the groat because the whole grain concentration we measured was less than 3 ppm (Table 1). Unless blended with copious amounts of 0 ppm grain the other lots would not be marketable to millers; they could however be constructed into beef and/or dairy rations.

We were able to achieve varying levels of cleanout with each method. With the aspirator we varied windspeed and were able to create a range of cleanout from approximately 4-25%. With the Clipper we varied sieve size and were able to create a range of approximately 18-60% cleanout. There was no clear relationship between the amount of cleanout and a reduction in DON concentration when using the Clipper.  There was, however, a slight increase in test weight and a correlated decrease on DON when using the aspirator. This suggest that removing lighter kernels more so than smaller kernels can yield some reduction in DON concentrations.

Using germination test as a proxy for DON testing proved inconclusive as there was no correlation between the percentages of kernels that showed mycelium growth, indicative of the presence of the Fusarium graminearum spores in or on the kernels, and DON concentration in the grain sample.

So, for the time being, grain should be sent to the lab for a test to determine the best use for the grain. In the future we hope to continue to monitor for this important disease of oats and evaluate the potential for managing it with fungicides.