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Winterkill depresses nutritional quality of alfalfa

Dave Miller Published on 14 February 2011

The level of alfalfa winterkill affects forage quality because of increased grassy and broadleaf weed pressure. In general, grasses such as quackgrass and bromegrass will reduce the quality of the harvested forage while broadleaf weeds have less effect.

This quality loss becomes more important in high-producing dairy rations. Here are general rules regarding weeds affecting yield and quality from University of Wisconsin Extension Alfalfa Stand Assessment, Publication A3620:

•    Controlling grassy weeds will improve forage quality but not yield.
•    Shepherd’s purse and white cockle have little impact on forage quality.
•    Dandelions lower the quality of the first forage cutting but have little effect on later cuttings.
•    Hoary alyssum and yellow rocket always seriously hurt forage quality.
•    Producers may use herbicides for reasons other than forage quality.
(Example: Dandelions are wetter than alfalfa and increase drying time.)

Below are a few scouting tips once alfalfa starts to green up:

Early spring signs
Check for bud and new shoot vigor. Healthy crowns are large, symmetrical and have many shoots. Examine them for delayed green-up, lopsided crowns and uneven shoot growth. If any of these characteristics are present, investigate further by checking for root rot and broken roots.

If heaving is evident, dig up some plants to determine if the taproot is broken. Plants with broken taproots may green-up, but they perform poorly and eventually die.

Slightly heaved plants can survive, but their longevity and productivity will be reduced. Crowns that heaved 1 inch or less are not as likely to have a broken taproot.

With time, these plants can reposition themselves. Raised crowns are susceptible to weather and mechanical damage. Raise cutter bars to avoid damaging exposed crowns.

Using a cultipacker or roller to push the crowns back in the ground can do more harm than good by damaging crowns and breaking taproots.

Stem counts
When alfalfa growth reaches 4 to 6 inches, use stems per square foot to assess density measure. A density of 55 stems per square foot has good yield potential.

Expect some yield loss with stem counts between 40 and 50 per square foot. Consider replacing the stand if there are less than 40 stems per square foot and the crown and root health is poor.

While weather is unpredictable, the risk of winter injury can be offset by selecting multiple disease-resistant, winterhardy varieties, maintaining young stands and adequate soil levels of potassium (K).

Adequate levels of potassium promote vigorous and healthy alfalfa growth as well as help protect against winter injury.  FG

Dave Miller is a Pioneer alfalfa research director based in Arlington, Wisconsin. Contact him at .

Dave Miller
Director of Alfalfa Research