NDSU Extension - Stark & Billings County

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Disease Concerns for Wheat Still in the Field

What is the relationship between Fusarium Head Blight (Scab) and Deoxynivalenol (Vomitoxin)?

Reports of high vomitoxin have been received from across North Dakota. Vomitoxin does not randomly occur in wheat, rather it is the by-product of the Fusarium fungus colonizing the wheat head and causing scab. The infection event for Fusarium generally occurs during the flowering stages of wheat. As the Fusarium fungus colonizes the wheat spike, kernel development is inhibited and vomitoxin is produced. The vomitoxin is very heat stable and will remain in the kernels and plant parts.

 

Will Vomitoxin increase in Wheat Left in the Field?

 

The Fusarium fungus is present on infected spikes and it is possible that the levels could have increased when conditions were favorable Fusarium growth (ie: high humidity, 70-80F, prolonged periods of moisture). However, it is also important to point out that vomitoxin is water soluble and experiments have shown that vomitoxin levels are lower after a single wetting event 7 to 28 days after infection. Research from the University of Minnesota has demonstrated that after applying 5.2-inches of rain over the course of 6-hours, vomitoxin levels were reduced.

The Risk of Cattle Feeding on Standing Wheat

 

The US Food and Drug Administration has advisory levels for vomitoxin in humans and animals. The human advisory levels is 1 ppm in finished food products. The advisory levels for ruminating beef and feed lot cattle that are 4 months or older is 10 ppm and the food source cannot exceed 50% of their total diet. Before considering turning the cattle onto the wheat ground, you must consider the risk for vomitoxin in the field. Vomitoxin levels can vary greatly in a region, across fields and within a field. Vomitoxin levels reported in grain have been less than 1 ppm to more than 20 ppm.  The other concern with having cattle graze the wheat is that VOM levels are not only reserved to the kernels. Fusarium infection causes the most damage to kernels, but can also colonize other plant parts. This includes the rachis and stem tissue below the head and in some cases VOM levels have been shown to be higher in plant tissue than the kernels. The other disease to be aware of is ergot. Ergot is well adapted in the state with a very large grass host range including quackgrass, brome grass and small grains. The infection event for the ergot pathogen occurs at heading, and it is likely some fields had conducive conditions (cool and wet) for ergot this year. Ergot bodies may have fallen off wheat heads due to the longevity of the crop being in the field, but scouting should still be done prior to cattle grazing. Ergot bodies contain toxic alkaloids that have a higher toxicity in cattle when compared to vomitoxin

 

Can I use the high VOM lot for seed next year?

 

Using a high VOM seed lot is not associated with causing VOM issues in next year’s crop. The infection window for the scab pathogen and production of vomitoxin is during the flowering stages, not from a seed source. A high VOM seed lot will have Fusarium infected kernels increasing risks for seedling blight, root rot and uneven emergence. If you decide to use a high VOM lot, clean the seed, treat with a fungicide (will slightly improve germination percent), check the germination percent and adjust plant populations.

 

The Wheat Looks Gray and Has Dusty Spores

 

Mature wheat that has been standing in the field has likely been colonized by saprophytic fungi (sooty mold). These are basically bread molds that use the dead wheat tissue as a food source. Most of these fungi do not produce mycotoxins. However, Fusarium sp. can also act as a saprophyte, which can lead to the production of vomitoxin and another mycotoxin fumonisin.

 

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