The reason for the rest is to build carbohydrate levels in the root system. High carbohydrate levels reduce winterkill and increase the length of time alfalfa persists in a field. They help the alfalfa get off to a fast start the following spring and increase spring harvest yields.
Is a six-week rest period always necessary?
As with most things that deal with biological organisms, the correct answer isn’t simple. Richard Leep and Jeffrey Anderson of Michigan State University suggest that several factors need to be considered. They indicate that the risk of winter injury will be minimal if:
- There have been sufficient rest periods between cuttings during the season with at least one harvest with blos-soms.
- The alfalfa roots have a good level of carbohydrates.
- There is a gradual hardening off during fall months.
- At least 4" of snow are present throughout the winter months.
- The crop isn’t exposed to alternate freezing and thaw-ing during late winter or early spring.
Some university alfalfa specialists have developed a work-sheet to help determine the need for fall resting. They suggest that answering the following questions will help a grower deter-mine the need to fall-rest alfalfa.
How old is the stand? Research has shown that older stands are much more in need of resting than younger stands.
What is the alfalfa’s winterhardiness rating? If the variety is "moderately winterhardy," a fall rest period is more important than if it’s "very winterhardy."
What’s the variety’s disease resistance rating? If it only has resistance to bacterial wilt, it’s much more sus-ceptible to winter injury than if it has resistance to several diseases, including bacterial, verticillium and fusarium wilts; anthracnose; and phytophthora root rot.
What’s your soil pH? If it’s below 6.0, you’ll have more risk of winterkill than if it’s over 6.5.
What is your soil potassium (K) level? Alfalfa is much more susceptible to winter injury if grown in low-K soils than in high-K soils.
What is your soil drainage? Fields with poor in-ternal and external drainage are more susceptible to winter injury than those with good drainage.
What insect damage occurred through the year? If your alfalfa was yellowed by potato leafhoppers during the sum-mer, it should definitely be fall-rested.
What is the fall soil moisture? Going into win-ter with wet soils increases the need for a fall rest period.
How frequently do you cut alfalfa? Fields with cutting intervals that exceed 35 days are less subject to winter injury than those with cutting intervals of less than 30 days.
Do you have at least 6" of stubble going into win-ter? Less stubble decreases the field’s ability to hold snow to protect the crowns from cold temperatures. It also increases the risk of late winter and early spring heaving.
Do you really need a six-week rest period in the fall? As you can see from the factors discussed above, the correct answer is "Not always." But if you want to maintain an alfalfa stand for the longest time possible, a six-week rest period removes a lot of the risk.