By: Nadia Mori PAg, Regional Forage Specialist, Watrous
If not properly managed, alfalfa can suffer winter injury or winterkill. Several factors play into good winter survival of your alfalfa stand.
Taking a Second Cut
For alfalfa, early fall is a critical time, as plants are storing nutrients needed to survive the upcoming winter. Cutting plants during this period adds double the stress to the plants as they have to expend energy for regrowth and nutrient storage. During a minimum of six weeks after cutting, alfalfa plants need good growing conditions to ensure sufficient regrowth and energy storage to support winter survival. Plants harvested after Aug. 15 may not have six weeks before a killing frost and may be susceptible to winter kill. A killing frost is considered -5 C or lower. Harvesting after a killing frost does not affect food reserves, but reduces the amount of stubble that helps trap snow. The trapped snow provides an important insulating blanket for alfalfa crowns.
If alfalfa makes up 50 per cent or more of the production in the stand and was properly inoculated at seeding, nitrogen is generally not a concern in the forage stand as the alfalfa will fix the nitrogen required by the stand. Phosphorus, potassium and sulphur are the three nutrients that should be considered in stands with large proportions of legumes. Phosphorus and potassium are particularly important, as they support root and nodule health and over-wintering capability. Both of these nutrients can be fall applied, as they are relatively immobile in the soil and will not leach or volatilize to the atmosphere like nitrogen. The most cost-effective way to maintain adequate soil fertility is to do a fall soil test.
An otherwise healthy stand can be impaired by insects and disease such as alfalfa weevils and downy mildew. Scouting for insects during June is important in noticing and minimizing insect feeding damage, while disease-resistant alfalfa varieties are your best defense against various root and leaf diseases.
Not all factors in alfalfa fall management are under your control. For example, dry conditions may have added additional stress on plants while wet soil conditions in the fall can reduce the plants’ ability to harden prior to winter. Lack of snow cover is also a concern, as alfalfa crowns can be exposed to extreme cold. Snow cover can be improved by leaving sufficient stubble height.
Planting cold-tolerant and disease-resistant varieties along with a good fertility program and careful cutting management will help winterize your alfalfa stand for better longevity and productivity.
For more information, please contact your Regional Forage Specialist or the Agriculture Knowledge Centre at 1-866-457-2377.