Evaluate Forage Stands for Winter Injury
Winter-dormant perennial forage plants remain dormant as long as temperatures in the ‘crown’ area, or upper few inches of the soil remain between about 0oF and 35oF. Snow cover and residual vegetative cover help to insulate the soil and stabilize soil and crown temperatures. Under ideal conditions, as spring temperatures warm through March, the plants ‘break dormancy’, and regrow normally into the spring. Winter injury and winter kill can occur under several conditions: if there is no snow cover and crown temperatures go much below 0oF; when mid-winter ‘warm spells’ cause the plants to ‘break dormancy’ early and are then more susceptible to late-winter cold crown temperatures; and, when plants are submerged in frozen, ponded water in low-lying areas during the winter.
This winter, the crown temperatures have likely not been cold enough for direct cold injury, even without snow cover. While day temperatures have been warmer than normal for short periods through February and early March, night temperatures have, hopefully, been cold enough to prevent the plants from breaking dormancy. A significant concern are the localized, frozen, ponded areas. How well did they handle this winter? It is time to go find out.
When evaluating alfalfa in late winter for winter injury, consider both the number of plants per square foot, and for alfalfa, the age of the stand. Crown and root diseases also have a major effect on stand reduction of legumes, so plants should be checked for dead, dying, or diseased crown and root tissue. Winter-injured plants may survive satisfactorily, but are often slow to recover in spring, so a quick decision to destroy a winter injured stand is not recommended.
Wait until the spring regrowth is about 3 to 4 inches high. Select random stand count sites. Check at least one 1-square-foot site for every 5 to 10 acres. Dig up all of the plants in the 1-square-foot area. Inspect for new growth and the crown and buds to determine if the tissue is still alive. Then count the number of live plants per square foot. Use Table 1 to begin your rating of the stand. Next, split the taproots and evaluate their general health. The core of a healthy taproot is firm and creamy-white. Damaged or dying taproots are yellowish-brown to chocolate-brown in color and watery or dry and fibrous in texture. Only healthy plants will contribute significantly to yield, so If the taproots are more than 50 percent diseased, reduce your initial stand count accordingly.
Table 1 Age of stand and rating of winter survival
Good Marginal * Consider Reseeding
Plants per sq. foot
Year after seeding +12 8 to 12 less than 8
2 +8 5 to 6 less than 5
3** +6 4 to 5 less than 4
4 and older ** +4 3 to 4 less than 3
* Healthy alfalfa plants in thin stands often produce more individual stems per
plant and compensate some in yield potential
** If 50 percent or more of the plants have crown or root rot, consider reseeding.
Plan your management this season, based on your stand evaluation.
• If stands are winter-injured, but will be harvested this season, allow plants
to mature to 10 to 25% bloom or later, before cutting.
• Increase cutting height to 3 to 4 inches
• Maintain good fertilizer and insect management
• If stands are severely winter injured, and you have incurred a significant
loss to planned stored forage, plan to reestablish a new hay field this
spring, and begin to plan for any needed supplemental harvested and
stored forage needed until the new seeding becomes adequately productive.
Assess red clover stands similarly.
Overwintering perennial forage grasses often survive better than winterhardy legumes. However, orchardgrass and ryegrasses are more susceptible to winter injury. Visual evaluation of grass regrowth and vitality of crown tissue is suggested when evaluating winter survival of pastures.
Reseeding in hayfields or pastures might be needed. Reseeding more alfalfa into or immediately after a 2-year old or older stand is not recommended. Overseeing or drilling grasses or red clover into thin or winter damaged stands should be done from now through April. Delaying seeding increases the risk of weed and surviving forage plant competition and seedling loss to increasingly dry and hot soil surface conditions of early summer.
Iowa State University Extension Publications for further information:
Evaluation for winter injury
Selecting forage species
Establishing new forage stands
Interseeding and No-till renovation
Stephen K. Barnhart
Extension Forage Specialist
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