Since early January, the weather has not been beneficial for alfalfa. This information may be beneficial when considering crop rotations this planting season.

The greatest concern is related to the sudden drop in temperatures in early January. In addition, the lack of snow at that time significantly increased the risk of winter injury.

In addition to weather conditions, other factors have been identified that have the potential to increase winter injury. Forage researchers note that older stands - greater than 3 years old - have greater risk of injury. There are significant variety differences in winter hardiness, as well. Most seed companies rate varieties for this trait. Varieties with better disease resistance will also be better able to tolerate poorer conditions.

Soil fertility plays a major role in winter survival. Fields with low soil pH and or low levels of potassium (K) have been shown to have greater winter injury from cold temperatures and heaving. Poorly drained soils also increase the risk of injury.

How does harvest management affect winter survival? More frequent cuts increase the risk, as does a fall harvest. Harvesting in mid-September, which allows some re-growth prior to frosts, has more winter injury risks than an early September or mid-October harvest. When cutting in the fall, a 6-inch stubble height is preferred.

In late March or early April, you should walk your fields to evaluate your stands. Look for uneven growth from plant crowns, both in location on the crown and in height. The best indicator will be found in the roots. Collect 4- to 6-inch lengths of roots and observe. Healthy roots will be firm and white, while winter injured ones will be grayish, possibly brown to black, and will be soft, stringy and possibly dry. On severely injured crowns, the top-growth can easily be pulled off.

One method to evaluate stands is based on counting stems per square foot at many locations across the field. Most productive alfalfa stands will have 55 stems per square foot. When counts are between 40 to 55 stems per square foot, there will be yield potential losses. At less than 40 stems per square foot, significant yield losses will occur and producers should consider replacing the stand.

If you decide to retain alfalfa stands with significant winter injury, consider the following practices to put some additional vigor back into the stand.

First, delay harvest to allow weakened plants to replenish carbohydrates needed for future production. How long should one delay harvest? This will depend on the extent of injury - less injury will need less of a delay. Initial cut of the most severely injured stands should be delayed until mid-bloom if the stand will be kept in production.

With only mild injury you may need to delay harvest to 10 or 25 percent bloom on one or two harvests, perhaps only the second or third cut. When delaying harvest, be sure to check the crown area for new growth. Removal of these new shoots will further weaken the plant, so be sure to cut before the new growth is tall enough to be affected.

Be sure to soil test and top dress. Potassium is a critical alfalfa nutrient that is frequently limiting production. Removal rates of 60 pounds per ton need to be replenished. Weed and insect control will also improve alfalfa survival.

What about interseeding on the worst stands? Experience and research has shown that this is not a beneficial practice. Established alfalfa plants produce a toxin that greatly inhibits development of smaller plants. Research has found that the risk remains in fields for 12 months. Rotating corn will be the best alternative to thin stands.