UACES Facebook Chance of Frost Increases Danger When Grazing Johnson Grass
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Chance of Frost Increases Danger When Grazing Johnson Grass

Grazing Johnson grass after a frost can be dangerous to your livestock.

Nashville, Ark. – As we start getting into colder temperatures, and frost will start occurring across the state, what happens to Johnson grass? And why does it become dangerous to graze Johnson grass?

When Johnson grass becomes stressed, it can produce a toxin called prussic acid also known as hydrocyanic acid, which is very toxic to livestock. Before a producer sees that his cattle are under stress from prussic acid, the cattle will die from the toxicity.

Besides Johnson grass there are other forages that can produce prussic acid. Sorghum/Sudan, Green graze, Grain Sorghum, and forage Sorghum all can produce prussic acid. When these forages become stressed from frost, they can become toxic. These forages should not be grazed after a hard frost until the plants become completely dried out. You want the forages to be a paper brown color when dried out.

John Jennings extension forage specialist says, “To reduce risk even farther, do not graze at night when frost is likely, don’t turn hungry cattle directly out on a Johnson grass pasture. Make sure they have grazed other forages first or fill them up on hay. Prussic acid dissipates as the plants dry out. Properly dried Johnson grass hay does not contain prussic acid and is safe to feed. Silage may contain toxic quantities of prussic acid, but it usually escapes in a gaseous form while being moved and fed. If frosted forage is ensiled, allow fermentation to take place for at least six weeks before feeding”.

For more information call the Howard County Extension Office at 870-845-7517 and ask for Carlie Bothum. You may also request a copy of FSA 3069 on Prussic Acid.


By Carlie Bothum
County Extension Agent - Agriculture
The Cooperative Extension Service
U of A System Division of Agriculture

Media Contact: Carlie Bothum
County Extension Agent - Agriculture
U of A Division of Agriculture
Cooperative Extension Service
421 N. Main Nashville AR 71852
(870) 845-7517


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