Cannon County has experienced its first killing frost of Fall. Due to the lengthy period of moisture, many of us failed to complete the second cutting of hay. Anytime adverse weather(drought) or a weather event (frost) happens, one of my first concerns is safety of cutting johnsongrass or sorghum x sudangrass hybrids for hay after frost.
Prussic acid (cyanide) that is released after a frost is a danger for grazing animals. The prussic acid will break down over the course of 7-10 days, so if the grass is cut for hay, by the time the haymaking process is complete, the danger from prussic acid poisoning is gone.
Producers can make hay or haylage from frosted johnsongrass or sudex, but they do not want to graze it. If they want to save it for grazing, they need to wait until the grass has been completely killed by frost, then wait 10 days prior to grazing.