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Evaluate forage stands for injury

It’s been an unusual winter — warmer than most and not much snow cover. Although winter was mild, you should still get out and evaluate alfalfa fields, mixed hay fields, pastures and other perennial forage plants. Now is the time to do it, says Steve Barnhart, Iowa State University Extension forage agronomist.

Assessing forage stands every year to get a handle on their health is an important and economically sound practice. Barnhart offers advice on what to look for and how to manage stands based on amount of damage and your stand count.

Perennial forages respond to the cooling days of autumn and “cold-harden” to their genetic winterhardiness limits, he explains. As long as temperatures in the crown area, or upper few inches of soil, remain between near zero and 35 degrees F, the plants stay dormant. Snow cover and residual vegetative cover help 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 spring.

Key Points

Check alfalfa and other forage stands this spring for signs of winter injury.

Amount of injury to plants will depend on weather and management factors.

Reseeding of hay fields or pastures may be needed if there is significant damage.

Winter injury and winterkill occur most often in Iowa if crown temperatures go much below zero degrees, and when mid-winter warm spells cause plants to break dormancy early, causing the recovering plants to become more susceptible to late-winter cold-crown temperatures. Freezing of ponded water in low-lying areas often causes localized spots of winterkill.

This past winter, crown temperatures weren’t likely cold enough for direct cold injury, even without snow cover. While day temperatures were warmer than normal through February, night temperatures were, hopefully, cold enough to prevent plants from breaking dormancy.

When evaluating perennial forage stands for winter injury, consider both number of plants per square foot, and for alfalfa, age of the stand. Crown and root diseases also have a major effect on stand reduction of legumes, so alfalfa 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 isn’t recommended. Instead, follow these steps:

    Wait until 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 the plants in the 1-square-foot area. Pick at the crown and buds with a knife to determine if tissue is still alive.

    Count the number of live plants per square foot. Use the table accompanying this article to begin rating 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, and watery or dry and fibrous in texture. Only healthy plants will contribute significantly to yield; if taproots are more than 50% diseased, reduce your initial stand count accordingly.

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 or 4 inches. If stands are severely winter-injured, and you’ve had significant loss and a setback for your plans for stored forage, plan to re-establish a new hay field this spring. Also, begin to plan for any needed supplemental harvested and stored forage that will be needed until the new forage seeding becomes adequately productive.

Check red clover stands the same way as alfalfa stands. As for grasses, “perennial forage grasses often survive better than winterhardy legumes,” says Barnhart. “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 more alfalfa into or immediately after a 2-year-old or older stand isn’t recommended. Overseeding, or drilling grasses or red clover into thin or winter-damaged alfalfa stands should be done from March through April. Delaying seeding increases risk of weed and surviving forage plant competition and seedling loss to increasingly dry and hot soil-surface conditions of early summer.

Source: ISU Extension


This article published in the April, 2012 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2012.