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Does Crown Rust in Oats Cause Problems for Livestock?

Updated July 14, 2021
Russ Daly

Russ Daly

Professor, SDSU Extension Veterinarian, State Public Health Veterinarian

Oat plants exhibiting crown rust symptoms.
Figure 1. Oat plants exhibiting crown rust symptoms.

Weather conditions present a variety of challenges for farmers and livestock producers. When wet, cool conditions predominate in the spring, one of those issues for crop producers can be crown rust in oats. When this crop disease is abundant, questions from livestock producers arise. Could crown rust in oats harm livestock if it’s present on pasture or in hay?

Crown rust is the most-important fungal infection of oats. This fungus can overwinter in certain plants and crop residue. Cool, wet springs provide the right conditions for crown rust to build up on the alternate plant hosts, making it readily available to affect oat plants as they grow. In years when oats are planted late, or as alternate crops on fields where corn or soybeans couldn’t get planted, the timing can be right for heavy rust infestations. Interestingly, crown rust doesn’t affect grasses or crops besides oats.

Affected oat plants will show small orange-yellow spots on the leaves, which can coalesce to the point where most of the leaf appears yellow or orange (Figure 1). Oat fields affected by rust can suffer drastic declines in yield.

Some fungal infections of grains and forages can certainly affect livestock, but crown rust of oats does not appear to be one of them. When fungi (molds) affect livestock feedstuffs, there are two different considerations: toxins produced by the mold (mycotoxins) and the mold spores themselves.

No known mycotoxins are associated with crown rust in oats. This means that if there are any biochemical byproducts produced by the rust organisms, they do not significantly affect livestock – including pregnant or growing animals.

The mold spores themselves may have sporadic effects on individual animals. Anyone who’s harvested “rusty” oats is aware of the dustiness in infected crops when windrowed, baled or combined. The suspension of mold spores in hay or forage (particularly horses) could result in instances of “heaves” –inflammation and constriction of the small airways, creating breathing problems in sensitive individual animals. These issues are not specific to crown rust in oats and could occur with dry hay infected by any number of mold species. If rust-affected oat hay is to be fed to horses, moistening the forage should be considered when its fed indoors.

Although crown rust does not directly affect animal health, its presence could affect feed quality or palatability. Livestock producers would be well-advised to consult a nutritionist or veterinarian if feeding oat forage affected by crown rust.