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Sorghum Sudangrass and Alfalfa Q &A to the Chouteau County Extension Office
Citations come from Emily Glunk/Meccage (MSU Extension Forage Specialist) and Dennis Cash (Retired MSU Extension Forage Specialist).
When is it safe to hay or graze my alfalfa in the fall? Harvest or graze the alfalfa after several days of consecutive killing frost, once the plant is dormant and will not be attempting to regrow before the winter (Glunk, 2017).
What does it take for a killing frost in alfalfa? Usually it takes about 3 days of less than 24 degrees to get the plant to shut down. (Meccage, 2018)
How do I minimize the chance of bloat when grazing alfalfa? Avoid grazing actively-growing pure alfalfa stands as well as alfalfa immediately after a light or heavy frost. Wait at least 3-5 days after a killing or light frost before grazing (Glunk, 2017).
Will fall grazing affect alfalfa longevity? Just as a warning, there have been studies out there that show taking that extra fall cutting can negatively affect the stand regrowth next spring if we have a mild winter, as it may break dormancy and cause some issues. However, this is somewhat common practice in Montana, and is not usually a problem (Meccage, 2018).
What is the minimum alfalfa vegetation going into winter? To maintain the health of the plant, producers should try to maintain a field average of at least 3 inches of growth which helps with reducing the negative effects of snow cover and ice sheeting (Glunk, 2017).
I need to hay my sorghum/sudangrass. Should I be concerned about prussic acid? I don’t worry about testing for prussic acid in hay. The acid levels start decreasing as soon as the sorghum/sudangrass is cut, and usually show up in the lab as non-detect. The prussic acid levels should decrease to a safe level after several weeks. If they want to bale it up and let it set before feeding, they should not have an issue. It is when we are trying to graze sorghum/sudangrass that I get nervous (Meccage, 2018).
When should I graze sorghum/sudangrass that tested positive for prussic acid? If hay shows high prussic acid or nitrates, sorghum/sudangrass should not be grazed until after a killing frost (Cash, 2005).
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