Alfalfa Winter Injury & Kill: Top Contributing Factors

By Karla Hernandez

SDSU Extension Forages Field Specialist

Main concerns about alfalfa production during this time of the year are the potential for winter injury and winter kill. In this article, a description of factors that affect alfalfa plants is discussed.

Winter Injury: Idetification tips

Here are some tips that will help you get started on where to look for possible winter injury:

• Stands which are slow to green up.
• Compare your stand to other fields in the area.  If you notice that some areas are starting to grow and other areas of your alfalfa field still brown, it is time to check those brown stands for injury or death.
• Winter-killed roots will have a gray appearance.
• If the root is soft and water can be easily squeezed from it, or it has a brown color, it is a possible sign of winter cold-related death.
• Asymmetrical growth and uneven growth.
• These are also two indicators of winter injury. Compare the shoots on the same plant, and if you notice that one set of shoots seems to be drastically outperforming another in terms of growth, it could be that winter cold damaged the bud structure of your plants.

Winter Kill: Top 6 factors

Top six factors that could affect alfalfa plants leading to a winter kill:

• Stand Age.
• Older stands are more likely to winterkill than younger plants.
• Soil pH.
• Soils with a pH above 6.6 are less likely to experience winter injury.
• Soil fertility.
•  Stands planted in soils with high natural fertility are less likely to experience winter injury than those with low fertility.
• Variety:
• Alfalfa varieties with superior winter hardiness ratings and a high disease resistance index are less likely to experience winter injury.
• Cutting Management.
• Harvest frequency and timing of fall cutting will affect alfalfa winter hardiness. The general trend shows that the shorter the interval between cuttings during the growing season, the greater risk of winter injury. An aggressive harvest schedule prevents the plant from storing carbohydrates in its root structure which it will need to maintain health as it regrows.  Stands in which last cutting is taken between September 1 and middle of October are at greatest risk, as plants did not have enough time to accumulate adequate carbohydrate levels in the root system before winter.
• Snow Cover.
• Snow provides insulation to the plants and the crown. The crucial temperature region is two to four inches below the soil surface where a large part of the root structure is located. Stands that have at least six inches of stubble left will be able to retain more snow cover and be less susceptible to winter injury.