Wallace's Farmer, IA
04-24-07
Check Alfalfa Stands For Frost Damage
Rod Swoboda rswoboda@farmprogress.com
Was there any damage to alfalfa stands in Iowa from the late freeze that hit a few
weeks ago? Yes, there is some, and now is the time to check your field by
digging a few plants and looking at the roots.
"Degree of damage is the question," says Steve Barnhart, Iowa State
University Extension forage agronomist. "Most of the alfalfa grown in Iowa is
considered winter hardy or cold hardy because of the genetics of the variety.
Under normal conditions the alfalfa plants go through their fall hardening,
develop a very good tolerance of cold temperatures and stays protected that way
all through the winter and then recovers in the spring."
It unfortunately loses it's winter hardiness and becomes a little more susceptible
to frost and cold temperatures. "That's what we experienced during the first
couple weeks of April," he says. "The new shoots that developed definitely got
frozen back. The unknown is whether the crown, which is stem tissue and upper
taproot tissue that is below the soil surface, was damaged or not due to cold."
Look at the condition of the crown
Is the crown below ground level in April? It's anywhere from a half inch to as
much as 2 or 2.5 inches below the soil surface, says Barnhart. What if you had
winter heaving of the alfalfa plants in your field? Heaving is a physical process of
freezing and thawing that actually squeezes the plant's carrot-shaped taproot up
out of the ground over the course of the winter.
"Definitely, if the plant was heaved and the crown was elevated above the
surface, then that would have killed that particular plant," he says.
A lot of times you lose quality in alfalfa. Barnhart says most alfalfa will recover
and grow out of the frost damage. But you are expecting at least three and
hopefully four strong, good-quality cuttings of alfalfa during the season. Now it is
going to be behind due to the frost. So you are not going to get one of those later
cuttings at the end of the growing season.
What this means is the first cutting will be later than normal this year in frosted
fields, but plants will eventually grow back. The first cutting may be higher quality
- not as stemmy since the plants have to grow back after the frost - but there
won't be as much hay in terms of quantity.
How to evaluate an alfalfa stand
Go to a field and dig some representative plants. Look at the crowns. You usually
see the crown where the stems are separating at the top of the taproot. "Look for
new, green shoots that are developing and starting to grow," advises Barnhart. "If
you don't see green, pick at the crown with your fingers or pocket knife to find out
whether the plant is alive or dead at this point."
The crown should be fairly firm. "You should take a knife and split the taproots of
some plants," he says. "A healthy taproot has creamy white tissue inside and firm
in texture. Winter-injured or frozen taproots start turning mushy, will turn a yellow
tan color, and watery. You should look at the upper inch of that taproot for that
watery appearance. If it's uniformly firm and white all the way to the top and you
are seeing some green tissue, that's a good sign."