Central Michigan alfalfa appears free of frost damage despite cold mid-May weekend
Even though much of Michigan’s Lower Peninsula experienced low temperatures in the mid to upper 20s on May 13, 2013, the alfalfa in Central Michigan seems to have escaped without any significant frost damage.
Low temperatures could affect the growth of both established forage plants and newly emerged seedlings. Several days after a frost, fields should be scouted to determine if plant tissue, crown or taproot was damaged.
It is important to monitor alfalfa growth early in the growing season so that forage yield and quality are maximized for the dairy herd. Tracking growing degree days (GDD) or taking measurements using a PEAQ (predictive equations for alfalfa quality) stick will result in better quality feed than by going from previous calendar dates of when alfalfa is typically ready for harvest. With hay inventories short after the drought of 2012, it may be tempting to take hay early, but it will pay in the long run to wait until the GDD indicate it is the proper time to harvest. If necessary, preserve the life of the stand by securing other feedstocks to get through until hay is ready to harvest.
GDD provides a measure of heat unit accumulation. Because early season growth of alfalfa is related to the sum of heat units accumulated, monitoring GDD is an easy and effective way to determine when to harvest to optimize forage quality of first cutting alfalfa. The measure of fiber most commonly used to balance diets of lactating dairy cows is neutral detergent fiber (NDF). The optimum concentration of NDF for alfalfa fed to lactating dairy cows is 40 percent. Michigan State University Extension recommends that dairy hay should be harvested at the mid-bud stage of growth – which will normally provide 40 percent NDF to maximize the yield and quality of feed to lactating dairy cows. Alfalfa containing 40 percent NDF allows reasonable grain concentrations in the diet while maintaining adequate NDF concentrations. Research at Michigan State University demonstrated that both GDD (growing degree days, base 41 degrees F) and PEAQ (predictive equations for alfalfa quality) provide good estimates of NDF for first cutting alfalfa in normal years.
For alfalfa, GDD is based on the minimum and maximum daily temperatures beginning March 1, using a base of 41F. The daily calculation is [(maximum temp + minimum temp)/2] - 41. The GDD accumulation is the sum of the daily GDD values across days beginning March 1.
Recommendations are to begin cutting alfalfa at 750 GDD for upright silos and 680 GDD for horizontal silos. According to data collected in the upper Midwest over several years, alfalfa typically averages 38 percent NDF at 680 GDD and 40 percent NDF at 750 GDD. Filling horizontal silos with layers of alfalfa of increasing maturity will allow harvest to begin a little earlier because the layers of alfalfa are blended as the alfalfa is removed from the silo.
The warm weather in early May 2013 helped to overcome some of the cold April we experienced, although depending on where you are located in the state and the weather over the next few weeks, harvest could be in the normal timeframe, or up to a week delayed. It is noteworthy the map below is using degree day base of 50F, and alfalfa cutting model uses a base of 41F, but the relative change between years is the same.