With an early cold snap in Nebraska, portions of the state may experience a non-killing frost, and fields in low areas may be especially vulnerable. This will continue as we transition into fall with frosts occurring that do not kill our current stands.
A non-killing frost ranges from 32-30°F, with a killing frost occurring at 29-24°F for four to six hours. The determination between a non-killing and killing frost is crucial when making management decisions, especially cutting or grazing.
In the case of non-killing frosts, typically we can see a deterioration at the tip of the alfalfa plants, with wilted and slightly curled leaves. If the light frost occurs for an extended period you can see some bronzing on the leaves as well.
It is important to note that these alfalfa plants will continue to grow, but their quality will decrease as fall continues. If cut following a non-killing frost regrowth will continue to occur at the crown buds and the plant will begin to utilize stored sugars, possibly affecting winter survival and spring vigor.
Once the hard frost occurs the stand can be cut. Harvest and grazing needs to take place shortly after following the killing freeze to maintain as much of the nutritive value as possible. Bloating can be a risk when stands are used for grazing.
Remember, this should really only be completed if you need the forage. Damage to the stand and increased exposure to environmental conditions can negatively affect the stand over winter and into the spring.
Bottom line: with non-killing frosts it’s better to leave the forage standing and wait for the killing frosts, if you are needing more forage this winter.