Conditions for survival seemed favourable going into the winter after a long fall of slowly dropping temperatures. However, the lack of snow cover for short periods when low temperatures hit Eastern Ontario could mean another good year for seed sales at the expense of farmers.

In many cases, fall dormancy is closely related to winter hardiness. Plants (Maple trees are a good example) that get ready for the winter by going into dormancy early seldom experience winterkill.

By contrast, alfalfa that originated in the mild Mediterranean region is less inclined to go into fall dormancy and is often vulnerable to winterkill.

A good predictor of an alfalfa variety’s ability to survive the winter is to measure the rate of fall growth. Varieties with short slow growth in the fall are best able to survive the winter. It is the task of plant breeders to develop modern varieties which continue to grow in the fall yet have improved winter survival. The trick may be to select lines with high root sugar concentration and high protein levels needed for survival and early spring growth.

While most management techniques focus on the accumulation of carbohydrates, the amount of freezable water in the tissue may have a greater impact on survival. Solutes such as potassium may act as antifreeze preventing ice crystal formation. Since plants will accumulate potassium in the fall, close monitoring of soil fertility and an early application of potash will improve survival. There is a range of damaging temperatures from about minus 5°C for non hardy varieties down to minus 25ºC for the hardiest varieties.

Good nodulation of alfalfa is essential for accumulation of root protein reserves. This is achieved by a high soil pH, excellent drainage and by not defoliating the plants during the fall critical period. Since newer varieties may have more growth in the fall the temptation is to harvest during the fall critical period. This practice may well compromise winter survival even with improvements in winter survival.

Plan to act quickly in the spring. Evaluate fields as soon as new growth appears. The best tools are a shovel and a knife to cut a cross section of roots. Examine for discolouration and dead tissue.

The major problem reseeding into alfalfa is the allelpathic reaction or self toxicity. Alfalfa roots give off toxic substances that impair the germination and subsequent development of alfalfa seedlings. This can be a greater problem when older stands have been killed that have accumulated greater amounts of toxic chemicals.

If this is the case, it is best to go out of alfalfa for a year since the toxins can persist up to six months. In the case of a newer stand or one without much alfalfa, the stand can be sprayed with glyphosate (e.g. Roundup) and then wait for two to three weeks before attempting a replant. If it was a new seeding such as a summer seeding that was killed you can simply go ahead and replant since new seedlings do not produce enough toxins to pose a problem.

Thin spots in alfalfa can sometimes be improved by broadcasting red clover into the stand. The trick here is to put the seed on very early in the spring before the soil surface starts to dry out.