There was an early break in alfalfa dormancy in early- to mid-March. In some areas, significant alfalfa growth (up to 6 – 8 inches or more) was frost damaged when colder temperatures returned on March 30th (-7°C or colder). Damage was most severe in south-western Ontario, on good healthy stands with early, aggressive growth. Ironically, fall harvested fields that had slower regrowth did not appear as affected. In mild cases, leaves at the tops of the plants were wilted and discoloured, but plants should completely recover. In more severe cases, alfalfa stems have been frozen to various degrees and growing points have been destroyed.
The extent of damage will depend on the severity of the freezing. Frost damaged alfalfa plants usually recover and regrow from:
1. axillary buds on the lower parts of the plant, if lower stems are not damaged, and/or
2. newly formed crown buds.
It takes a lot of frost to kill an alfalfa crown. Compounding the recovery issue is the cooler temperatures and very dry soil conditions in early-April that have delayed regrowth. Some rain and heat are required to help these fields recover.
Should I Cut It Now?
There is no benefit to cutting frosted plants. Cutting will not enhance recovery. Yield will be extremely low with poor quality. Severe frost kills the growing points, the same as cutting does. Regrowth will have to come from new crown buds.
Impacts
Plants used up some of their root reserves for the initial March growth. These plants will now have to initiate regrowth from new crown or axillary buds, which will delay the growth and developments of the crop. Depending on weather conditions, anticipate some 1st-cut yield reduction and a delay in maturity. Where damage is uneven across a field, there could be some unevenness in maturity. If possible, delay cutting of severely affected fields to allow rebuilding of root reserves and full recovery.
Dig & Assess Crowns
It’s always advisable to walk alfalfa fields to assess winterkill damage, heaving and plant health by digging some plants (crown and root). It is a good idea to check crowns of severely frost-damaged alfalfa fields to determine if these plants are actually dead, before any drastic action is taken.
There have been some reports of winterkill from across the province this spring, but especially in eastern Ontario, and on heavier poorly drained soils, older stands and fields that were cut during the Critical Fall Harvest Period. There are also some reports of alfalfa heaving.
“Alfalfa Stand Assessment”
http://www.omafra.gov.on.ca/english/crops/facts/info_alfalfa_stand00.htm
“Frost Heaving of Alfalfa”
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