Answers to Frequently Asked Winter Grazing Questions

This week, Victor Shelton has answers to the most asked questions for winter graziers. Thanks, Victor! What is the difference between a frost and a freeze? When water vapor condenses and freezes without first becoming dew, a thin layer of ice crystals form – this is frost.  It generally has to be below 36 degrees to frost and include clear skies, moisture present and little wind. Plant tissue can be impacted, but not as severely as a freeze. When the surface air temperature falls to 32 degrees or below, you have a freeze. Generally, if it is above 29 degrees, it is a light freeze that can kill most tender plants. If it is below 28 degrees, then it is considered a killing freeze or hard freeze – this freeze kills annuals and initiates shutdown of hardy perennials. What are those forages that cause problems after a freeze? With frosts and freezing conditions, we do need to remember that some warm-season forages such as sudangrass and sorghum-Sudan hybrids, and johnsongrass produce a cyanide compound when frosted, causing the production of the prussic acid. Once these forages are frosted, livestock should be removed for at least two weeks to allow for the forages to “dry down” and the prussic acid to dissipate before grazing again. Frosted areas could start with only “pockets” in a field. Any regrowth from the base of the plant after a frost can also be very high in prussic acid. It is just safer to avoid until forages are brown and dry – if in doubt, t

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