Rainy Weather and Wheat Straw Quality

By:  Pierce Paul

Not only has rain delayed the harvest of some fields for grain, it has also delayed the baling of straw in several fields that have been harvested. In Ohio, wheat straw is sometimes just as important or even more important than grain, as it is used as bedding for livestock, and in some cases, as a feed ingredient. Delayed baling due to excessive rainfall could cause the quality of the straw to deteriorate as a result of mold growth. To fungi (molds), wheat straw is nothing more than dead plant tissue ready to be colonized. Under warm, wet conditions, saprophytic fungi (molds that feed of dead plant materials) readily colonize wheat stubble, resulting in a dark moldy cast being formed. This problem is particularly severe in lodged fields.

Some of the molds growing on the wet straw in the field, including the fungus that causes head scab (Fusarium graminearum), also produce mycotoxins such as vomitoxin. This could be a concern when using straw for bedding or as a feed ingredient. In general, vomitoxin levels are much higher in straw than they are in the grain, and even when the straw is used as bedding, a small portion of it is consumed. For instance, depending on the production system, pigs may obtain up to 12% of their total feed intake from straw. Pig are particularly sensitive to vomitoixin – it causes vomiting (hence the name), feed refusal, and low weight gain. A good way to tell if the straw is colonized by the scab fungus it to look at the color of the mold growing on it – a pinkish-white mold would be a good indication that the straw could be contaminated with vomitoxin.

Vomitoxin contamination of straw tends to be highest when the straw is baled from fields with high levels of head scab. In addition, straw from fields that were planted with head scab resistant variates usually contain less vomitoxin than straw from fields plated with susceptible varieties. Thankfully, head scab levels were very low in most fields across the state this year, as a result, initial vomitoxin levels in the straw may be low. However, straw from scab-free fields can still be colonized by the fungus and contaminated with vomitoxin, especially if it goes through repeated wetting and drying cycles before being baled. This would be even more of a problem for those fields that have not yet been harvested, as both the grain and the straw could be contaminated with vomitoxin. Moldy straw could also contain other mycotoxins that are harmful to livestock. So, in addition to examining the straw for mold growth (pinkish color), get a sample tested for mycotoxins before using it for bedding or feed.

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