With forage being tight this year as we head into winter, a late alfalfa cutting may be on your mind, but we need to take into consideration the impactions a harvest in later September or October have for next spring.
Typically alfalfa needs six weeks of uninterrupted growth before the average first frost to winterize. The winterization process itself can occur in as little as three weeks, but having a total of six weeks helps to mitigate risks by allowing the alfalfa to move stored reserves to the roots and become acclimated to changing temperatures. By planning on six weeks, we ensure any plants that need longer to winterize have the time to do so, as well as provide insurance against an early frost. Allowing alfalfa to successfully winterize is key to having productive stands next spring and reducing long term losses in your alfalfa stand.
Stress during the season also plays a role in the winterization process. Environmental stresses such as; drought, heat, hail, or frost cause slower regrowth and shorter stands in season. Even the amount of times we cut stands and the age of the stand are stress considerations. Therefore, if you are trying to push the six week rule, remember that alfalfa that has been heavily stressed throughout the season or older stands would benefit from having uninterrupted growth to complete the winterization process.
When planning your last cutting for older or stressed alfalfa stands, we can use dates for establishing fall alfalfa as a guide to timing a last cutting. While it can vary, for northeast Nebraska we recommend having fall stands seeded by early September. So the last cutting on a drought stressed stand, early September is also when we want to have harvest completed and stands starting to winterize. If we do push the harvest window later, remember that these later harvested fields will have a slow start next year and may have issues overwintering, both of which may impact yield next year.
When cold temperatures do come to call, the nature of the freeze we get will have an impact on management options. A non-killing frost ranges from 32-30°F, with a killing frost occurring at 29-24°F for 4 to 6 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 with low risk to damage the stand. Harvest needs to take place shortly following the killing freeze to maintain as much of the plant’s nutritive value as possible. Bloating can be a risk when stands are used for grazing especially immediately following the freeze event. Remember haying and grazing consideration should weigh need for forage with possibly harm to the stand and decreased production next year. Damage to the stand and increased exposure to environmental conditions can negatively affect the stand over winter and into the spring. Getting proper conditions to dry down hay fully in the fall is also an obstacle that needs consideration.
To recap: alfalfa needs at least six weeks of uninterrupted growth into the fall to be the most successful when it comes to winterization, edging into that six weeks is an added risk. Later cuttings can be possible for stands that are newer and have been under relatively low stress this season, but expect delays next spring. Once we reach the time of year when temperatures dip below freezing, leave forage alone after a non-killing frost. If forage is needed this winter, wait for a killing frost before any harvests.
-Ben Beckman is a beef systems Extension Educator serving the counties of Antelope, Cedar, Knox, Madison and Pierce. He is based out of the Cedar County Extension office in Hartington. You can reach him by phone: (402) 254-6821 or email: ben.beckman@unl.edu