There are better ways to determine when to cut first- and second-crop alfalfa for optimal quality than looking at stage of maturity or the calendar.

It's more accurate to use a PEAQ stick or calculate heat units, known as growing degree days (GDDs), says Richard Leep, Michigan State University (MSU) extension forage specialist.

“Visually analyzing the alfalfa for the best time to cut is subjective,” says Leep. “What's early bud stage to one grower isn't necessarily early bud stage to another.”

The PEAQ (Predictive Equations for Alfalfa Quality) method was developed in the 1990s by University of Wisconsin-Madison researchers. It uses plant height and maturity stage to estimate alfalfa quality. Sticks can be calibrated to measure NDF, ADF or RFV.

Alfalfa growers can begin tracking GDDs as soon as alfalfa plants break dormancy and actively start growing, says Leep. That's usually around March 1 in Michigan.

NDF increases about 0.04 point for each GDD. GDDs accumulate whenever the average daily temperature exceeds 41°, and can be as high as 40 GDDs/day.

“We recommend growers take their first cuttings when GDDs hit 750,” he advises. “That will give you 40% NDF, which is ideal for high-producing dairy cows.”

County extension agents compared four methods for timing cuttings at many sites on Michigan farms. They tracked GDDs, used PEAQ sticks and looked at the calendar or at physiological indicators like bud formation. Samples were analyzed using wet chemistry.

In the first cutting, the PEAQ and GDDs were equally effective at hitting the 40%-NDF target. In the second cutting, the PEAQ stick narrowly edged GDDs as the more accurate method. Both were better than the other two.

“Those two methods didn't work as well with subsequent cuttings because we tend to get into drier weather in July and August,” says Leep. “Once you get to later cuttings, use either hand clippings for analysis or growth stage.”

Whether to use a PEAQ stick or track GDDs is a matter of personal preference, he says. “On one hand, GDDs can be tracked from indoors, but using a PEAQ stick in the field gives you the opportunity to scout for insects and monitor plant health at the same time.”

Track GDDs using a thermometer that records the minimum and maximum daily temperatures or glean the information from a weather Web site, recommends Doo-Hong Min, an MSU extension forage specialist in the Upper Peninsula.

To calculate GDDs, average the minimum and maximum daily temperatures and subtract 41. For example, if the daily high and low temperatures are 65 and 43, the GDDs are 13 (65 + 43 = 108/2 - 41 = 13).

One final caution: GDDs should only be used with pure alfalfa, not alfalfa-grass mixtures, says Min.