According to measurements using a PEAQ (predictive equations for alfalfa quality) stick in Litchfield, Mich., on May 20, 2013 and monitoring growing degree days (GDD), alfalfa in SE Michigan is ready to harvest for dairy quality hay, with other areas in Southern Michigan close behind. With rain in the forecast through May 23, 2013, it will be important to harvest hay as soon as weather allows. Harvest hay with grass in it first, as grass matures quicker than alfalfa.
Damaged alfalfa fields above threshold from alfalfa weevil have been observed in Southeast Michigan. Fields with 40 percent damage and have larvae present should be cut as soon as possible for control. Timely cutting kills most larvae, pupae and some adults. Spraying an insecticide should be considered in fields above threshold that will not be cut in 7 days. Always read and follow insecticide label recommendations. Insecticides listed for control of alfalfa weevil are highly toxic to honeybees. Scout fields daily as harvest approaches and cutting early may be necessary if damage is extensive. For more information on how to identify insect damage, review Proper IPM for alfalfa weevils provides a basis for treatment.
Tracking GDD or taking measurements using a PEAQ stick will result in better quality feed than going from previous calendar dates of when alfalfa is typically ready for 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.
For alfalfa, GDD is based on the minimum and maximum daily temperatures beginning March 1, using a base of 41 degrees F. 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.
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 F) and PEAQ (predictive equations for alfalfa quality) provide good estimates of NDF for first cutting alfalfa in normal years.