Spring is here, or so we think. Much of the Midwest has experienced a blast or two of temperatures close to 80 degrees in the past few weeks. On the flip side, we’ve had some recent nights below freezing. This roller coaster of weather makes us scratch our heads and wonder how the 2021 alfalfa crop will be affected. Before we go into panic mode with alfalfa stands, let’s step back and assess the situation.  

Cold weather effects on plant growth
Remember that alfalfa is a frost-hardy plant. It takes temperatures below 24 degrees for more than four hours to freeze alfalfa top growth. That means the plant will most likely be OK if temperatures stay above that mark or only dip for a short period of time. That said, if it is cold enough for long enough, frost can kill the terminal bud at the top of the stem where new growth occurs. This bud is exposed to the elements making it most vulnerable.
The plant will try to grow if the terminal bud is killed, developing axillary buds at intersections of lower leaves of the stem, but it will not grow taller. Although the plant may continue to grow and produce some additional forage, yield will be depressed and, at some point, will need to be cut to allow for full regrowth for second cutting.  
If we experience cold temperatures in the coming weeks, work with your agronomist and forage advisers to assess alfalfa stands before rushing out and cutting immediately.

First-cut timing sets the pace for the rest of the growing season
When should you start first cutting? No simple guidelines apply every year or for every farm. Generally, you can wait longer during periods of cooler temperatures and wetter conditions. Warmer springs with adequate moisture lead to faster growth and more rapid decline in fiber digestibility. In the Upper Midwest, it is generally recommended by university researchers to plan the first cut near the accumulation of 700 growing degrees.
Plant maturity is the most important factor affecting quality. With increased maturity comes more cell wall constituents, including lignin, cellulose and hemicellulose. Proportionally, there is a drop in the digestible cellular contents such as soluble proteins, sugars, starch, fats and pectins. Not only does neutral detergent fiber increase and forage energy content drop with maturity, but also the accumulating NDF becomes less digestible.  

Scissor cuttings and PEAQ stick evaluation
Scissor cutting is a tool that has been around for many years to estimate preharvest quality. Select a field in the second or third production year, and sample twice a week until quality falls below desired harvest quality. Work with your nutritionist to determine target quality and implement proper scissor cutting procedures.  
A second tool, the Predicted Equation for Alfalfa Quality developed by the University of Wisconsin-Madison, helps make field estimates. The PEAQ stick involves measuring the tallest stems in a 2-square-foot area of the field and correlating to the plant maturity reading on the stick to estimate relative forage quality. Scissor cutting and PEAQ stick evaluation are generally more accurate as alfalfa height exceeds 15 inches. Both measurements evaluate the standing crop and do not account for the change in quality due to wilting, harvesting and storage. These losses will further lower relative feed value by 15% to 25%.  
Preharvest quality estimates have their greatest value for first crop. Calendar date and visual maturity are useful factors in gauging harvest time for later cuttings. The early bud stage is optimal for both yield and quality. Genetic technologies with lower lignin alfalfa may allow us to maintain nutritional quality over a longer window of harvest. This is most often utilized in subsequent cuttings after first-cutting.
The maturity and quality of alfalfa silage at harvest is only one factor affecting the bottom line of your dairy. Harvesting top-quality alfalfa silage should be a priority of your forage team. It’s in the best interest of your cows and your pocketbook.
Barry Visser is a nutritionist for Vita Plus.