BROOKINGS, S.D. — Winter injury and kill of alfalfa are the main concerns on forage producers’ minds this time of year, explained Karla Hernandez, SDSU Extension Forages Field Specialist.
Six factors which contribute to winter-kill include:
1. Stand age: older stands are more likely to winterkill than younger plants.
2. Soil pH: soils with a pH above 6.6 are less likely to experience winter injury.
3. Soil fertility: stands planted in soils with high natural fertility are less likely to experience winter injury than those with low fertility.
4. Variety: Alfalfa varieties with superior winter hardiness ratings and a high disease resistance index are less likely to experience winter injury.
5. 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,” Hernandez said.
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.
6. Snow cover: Snow provides insulation to the plants and the crown.
“The crucial temperature region is 2-to 4-inches below the soil surface where a large part of the root structure is located,” she said.
Stands that have at least 6-inches of stubble left will be able to retain more snow cover and be less susceptible to winter injury.
If your stand is impacted by the above conditions, Hernandez said scouting is necessary to clearly understand whether replant is necessary.
“Begin by looking to see which stands which are slow to green up this spring,” Hernandez said.
She encouraged growers to compare their stand to other fields in the area. “If you notice 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,” she said.
Examin the roots: 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,” Hernandez said.
Compare shoots: Asymmetrical growth and uneven growth 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,” Hernandez said.
If a grower thinks their stands have been injured, Hernandez outlines guideline in Table 1 to help decide whether to keep or replant the stand.
— SDSU Extension
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