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Fall is a critical period when it comes to managing winter hardiness or winterkill in alfalfa stands.
Range Management Specialist Trevor Lennox says alfalfa is thought of as queen of the forages.
"It's a very important forage, as a result, it's important to keep the stand as productive as possible."
He points out that when an alfalfa plant is cut, the initial regrowth that follows is produced from root reserves, as new leaves are developed, they begin to manufacture their own energy for growth.
"In the fall, this normally takes 4-6 weeks, and must be completed prior to the first killing frost (-5 degrees Celsius). As a result, this 4-6 week period is referred to as the ‘critical fall harvest period’. In the fall, the final cut should be timed either early enough to allow reserves to build up, prior to the first killing frost or cut late enough so that lower fall
temperatures prevent additional growth from occurring. "
Some factors in addition to cutting management that can also affect winter survival include:
-Choice of variety -choosing a variety with good winter hardiness
-Warm, moist fall weather that is unfavourable for hardening of the plants.
-Alternate freezing and thawing of the ground during the winter or early fall.
-Surface icing during the winter or early spring.
-Long periods of drought in the summer and fall, causing plants to dry out before or soon
after winter starts.
-Disease infection, causing weakening of the plants.
What can be done to reduce the risk of winter-kill?
-Maintain soil fertility levels. Alfalfa plants that are fertilized with adequate levels of
phosphorus, potassium, and sulfur are better able to resist and recover from diseases
often associated with winterkilling. Potassium has been shown to increase winter
hardiness.
-Seed hardy varieties. Plant varieties that have good cold tolerance. Follow proper seeding
guidelines and rates.
-Time the last cutting so there is at least 4-6 weeks before a killing frost. If the last cut is
taken within this time, the root reserves will be low going into winter.
-If feed is needed, consider harvesting after a killing frost. Higher stubble heights should be
left in order to catch snow and enhance winter survival.