By Dan Martens

For the first time for a few years, we've had a winter that provided a fairly good blanket of snow for alfalfa fields through the winter. This gives us reason to believe alfalfa will come through the 2007-08 winter better than it has in some recent years.

I heard some concern about the cold weather we got later in November before we had much snow, but that did not last long. Spring freeze and thaw cycles or a hard frost after the alfalfa breaks dormancy can still be a concern. An early April cold spell in 2007 (temperatures 10-15 degrees on a couple of mornings) contributed to alfalfa losses last spring. Hopefully, we're past that kind of weather.

It is good to make a practice of checking alfalfa fields as we approach the end of April and early May. Take a stretch break from tillage or planting work for a little walk in a nearby hay field. When alfalfa has grown to about 6 inches, you can take stem counts. It is generally thought that fewer than 40 stems per square foot may not be economical to keep. An average of 40-55 stems is borderline. More than 55 stems per square foot should provide excellent yield potential. Your experience on your farm is important.

When on-farm hay supplies are low, some farmers may prefer to take a first crop from marginal fields and consider breaking up the field to plant a different crop following first cutting. Corn silage is generally the crop with the greatest tonnage potential and can make good use of nitrogen credits provided by a past crop of alfalfa.

If spring growth seems very slow or spotty in a field, it can be useful to dig, and split roots to check for signs of root health that may provide clues for potential productivity in the field.

Forage and plant pathology specialists at University of Minnesota Extension and USDA-ARS (Paul Peterson, Dean Malvick, Charla Hollingsworth and Deb Samac) recently wrote about two diseases that we are watching for more closely in Minnesota in recent years. The first is brown root rot, a disease that can be favored by snow cover in some situations. BRR is most likely to be found stands older than one production year because the fungus grows slowly and depends on specific environmental conditions to develop. The fungus can infect the plant in the spring or in the fall. When it occurs in the fall, it can severely weaken susceptible plants and contribute to winter kill.

Aboveground symptoms of BRR include stunted or dead plants that are widely scattered through the field. Taproots will often have brown, sunken lesions. Moderately to severely diseased plants may start to grow in spring but die before the first cutting is harvested because the taproot has rotted. When this happens, the remaining root system is too compromised to support plant growth.

U-M and USDA-ARS staff are tracking the presence of BRR in Minnesota. If you see fields that fit the symptom descriptions, they will test root samples for presence of BRR. In Stearns, Benton and Morrison County, you are welcome to call the Extension Office in Foley (968-5077 or 1-800-964-4929) about suspect fields.

The second disease is aphanomyces root rot. This disease can kill and stunt seedlings. It is more of a problem with wet field conditions during germination, emergence, and early seedling stages. Infected plants usually have few fine fibrous and lateral roots and few nodules. Infected plants appear stunted, do not regrow well after cutting, and the foliage is yellow. Plants infected in the fall can be more susceptible to damage from root heaving with spring freeze and thaw cycles, especially on heavy clay soil.

We'll continue to be optimistic about the hay crop this spring and continue to make a practice of doing some scouting in fields as spring moves along.

Dan Martens is with the University of Minnesota Extension.