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OMAFRA: Be aware of frost injury risks in sorghum species

Christine O’Reilly, forage and grazing specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs, cautions growers of sorghum species who intend to use the crop as animal feed. She says that members of the sorghum family – sorghum, sudangrass, and hybrid sorghum-sudangrass – contain dhurrin, a glucoside that breaks down to release hydrocyanic acid, also known as prussic acid. A sudden disruption of growth – such as frost, drought or cutting – causes prussic acid to be released inside the plant at a more rapid rate. High prussic acid levels may be lethal to ruminants; death often occurs within 20 minutes of ingesting sorghum forage with elevated prussic acid concentrations.

Early fall, between the first frost and the first killing frost, is the riskiest time of year for prussic acid production in sorghum species, O’Reilly notes, as these warm-season grasses are very frost-sensitive. It is impossible to know by looking at them how much prussic acid is present in the plants. |READ MORE