Farmer, Wallace's IA 04-24-07 Check Alfalfa Stands For Frost Damage Rod Swoboda [e-mail] 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 surface, the 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 gr...