This week ISUEO Field Agronomist Joel DeJong notes that he has been in a few older alfalfa stands that did not survive the winter very well. Sometimes they looked OK from the road, but when in them you could see that the stands were thinned significantly by the winter we just experienced.
Young stands seemed to handle the winter adequately, but 4 or more year stands seem to have had some issues. Ideally, when the alfalfa is 6” tall, we can average 55 or more stems per square foot. If between 40 to 55 stems per square foot we would have yield reductions from 0 to 30%. Below 40 stems we should probably rotate. If plants are smaller than 6”, we would look for more than 12 plants per square foot in year 1 after seeding year, 8 in year 2, 5 in year 3, and 4 in years 4+. I would still re-evaluate when alfalfa is 6” tall. For more details on this discussion, see the ISU ICM News article titled “Scouting and Managing for Winter Injury in Alfalfa.”