Integrated Crop Management

Scouting for alfalfa winter injury

Mid- to late-March is the time producers should be inspecting alfalfa (and other perennial forage grasses and legumes) for spring recovery. The atypical weather this past fall and winter has led to considerable uncertainty about forage crop survival. Winter-dormant plants lose much of their cold hardiness during an extended period of warmer-than-normal air and soil temperatures, which is referred to as the January or February thaw. These plants regain some cold hardiness with the return of cold temperatures, but the magnitude of cold hardiness is lessened, leaving them vulnerable to tissue freezing at somewhat higher temperatures (teens and low 20s) compared with tolerance of 0 to 10°F soil temperatures of more normal "winterhardened" plants. Winterkill, winter injury, and slowed regrowth are more prevalent in alfalfa subjected to these "warmer" winters.

For the winter 2001-2002, I do not know how much cold hardiness the perennial forage plants achieved. In addition, extended warm periods all winter have contributed to what I have been seeing in the field as "green shoot tissue winter-long." Respiration rates have probably been high all winter, which may slow spring recovery. I am particularly concerned about the low-teen and single-digit temperatures during the last week of February, with no appreciable snow cover. Even a few inches of snow cover contribute to a more successful winter survival, regardless of the degree of winter hardening.



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Healthy alfalfa taproot.

Here are some tips for scouting alfalfa fields this March to determine the extent of winter injury.

This article originally appeared on page 21 of the IC-488 (3) -- March 18, 2002 issue.


Source URL:
http://www.ipm.iastate.edu/ipm/icm//ipm/icm/2002/3-18-2002/alfalfainjury.html