Watch out for vomitoxins in straw

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The wet spring we have experienced may lead to issues with wheat straw quality. During most of May, the wheat head scab risk assessment model had eastern Ohio in the moderate to high-risk range.

During wheat pollination, this tool can be used to assess if weather conditions are right for the fungus Fusarium graminearum to infect the wheat head and to make fungicide application decisions. The wheat is advanced enough now to walk fields and scout for head scab, which we are seeing across the state.

While that is a concern for marketing the wheat, it is also a concern for straw that is used in feed or even bedding. The highest risk is straw used for feed and for calf bedding.

One study shows that when the prepartum diet contained straw that was high in vomitoxins, 20-30% of cows had a short gestation length. The goal is for less than 12% of cows to have a short gestation length.

Finding vomitoxin

Vomitoxin in wheat straw can come from two sources. The first is infected wheat grain in the straw and the second is the straw itself. Studies have found a positive correlation between the amount of Fusarium head blight present in fields and the amount of vomitoxin in the harvested straw. Vomitoxin levels in wheat straw are often at least three times higher than in the grain.

When harvesting wheat that is infected with head scab, combine adjustments to clean the lightweight wheat kernels infected with head scab from the clean grain lead to these kernels being blown out the back of the combine into the straw.

When rainfall delays baling after wheat harvest, there is often an increase in straw vomitoxin levels. Straw storage is also a risk for increased vomitoxin levels. Anytime the straw is over 15% moisture, the fungus Fusarium graminearum can grow and produce vomitoxins.

In straw that is stored outside, we often find vomitoxin levels that are low after harvest. But, within three or four months, levels are high enough in some bales to cause toxin issues from the straw used for feed.

With head scab visible in many fields, it will be beneficial to scout fields that you will be baling straw in to determine which ones have the lowest head scab. Take good notes of where straw from each field is stored so that you can test for vomitoxin levels in the straw you will be feeding.

First, test the straw from the fields with the lowest head scab levels as they should have the lowest vomitoxin levels. Straw that will be used as feed should be stored inside or at least covered as soon as possible after harvest to keep it dry, preventing vomitoxin from increasing during storage.

Pricing your straw

If purchasing straw in the field from other producers, scout those fields also and discuss if fungicide was applied for head scab management to help determine your risk of vomitoxin in the straw. When pricing wheat straw there is the cost of baling and the value of the straw. The value of the straw lying in the field is at minimum the nutrients that will be removed. Each ton of wheat straw removes about 11-13 pounds of nitrogen, 3-4 pounds of P2O5 and 20-25 pounds of K2O.

Using the average price of fertilizer from the OSU 2024 second quarter fertilizer price survey these three nutrients have a value of $16.25 to 19.99 per acre. Besides those nutrients, when straw is baled, micronutrients, organic matter and residue to protect the soil from erosion are removed which is harder to put a price on.

If manure is traded for straw, the manure would contain as many of the micronutrients removed. One survey from the Midwest showed straw prices in the field to often be twice the value of the N-P-K removal. Another common strategy found was the value of the N-P-K plus the cost of planting a cover crop. The OSU custom rates survey shows custom no-till drilling a crop costs on average about $2/acre.

An NRCS cover crop bulletin has a seed cost of $5-25 per acre. A typical straw crop is 2-3 tons which, if using the cover crop price strategy, would increase the straw cost over the nutrient value by $8.66-23/ton. Just as high levels of vomitoxin hurt the wheat grain values, if you are buying straw for feed that is high in vomitoxin, this may need to be considered in the straw price.

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