Alfalfa survived the winter!

Craig Sheaffer, Extension forage agronomist

Figure 1. Alfalfa shoot emergence in March 2024.
At this stage exposed vegetation is mostly leaves
with little stem elongation.

We have had no reports of widespread alfalfa winterinjury. In an early March 2024 article on alfalfa winter survival, I indicated that alfalfa should have been in good shape up to that time because of the long fall dormancy period, the dry soils, above average air temperatures and soil temperatures in the 20-30F range. Temperatures of 5F are required to kill alfalfa root and crown tissues.

Figure 2. An alfalfa crown showing
initial spring regrowth from crown buds.

During early March, 2-4 inch soil temperatures did reach 40 F at several locations and alfalfa broke dormancy and crown buds elongated (Figure 1 and 2). Following this, we had some huge swings in air temperatures from record highs to single digit lows and lack of snow cover. There was concern about injury to the elongated crown buds because previous research had shown that at temperatures of 20F and less significant injury to herbage occurs. However, we observed no frost damage to newly emerged leaves. Also, we had no reports of heaving of crowns due to freezing and thawing of soils.

An early first harvest?

So far this spring, we have had above normal average air temperatures and the alfalfa in many areas is taller than normal. If this trend continues, we expect alfalfa to be ready to harvest earlier this year. The first spring harvest is the largest for the year and the goal should be to maximize the yields while obtaining quality goals. Earlier, we provided general guidelines for managing risks of the first alfalfa harvest.  In that article, we discussed developing a harvest schedule where alfalfa maturity at harvest varied to reduce seasonal risks. This “multiple goal” harvest scheduling included the following:

• A flexible first harvest at the first opportunity when weather permits at the end of May when alfalfa is from late vegetative to bud stage. Alfalfa flowers in response to the longer days of sunlight in spring but development is affected by air temperatures. In some years flowering does not occur until early June after the crop has lodged. So a first harvest scheduled by calendar date or canopy height should be considered. A strategy of taking the first harvest at bud or preflower will provide high quality forage but potentially result in less yield than waiting to flowering. Late May and June is typically a time when there is a high probability of rain so that having flexibility in harvest timing when adequate rain free days occur will reduce risk of rain damage during forage drying.
• Cut subsequent harvests during the summer when alfalfa is more mature to achieve higher forage yield. Allowing at least one harvest to reach the flowering stage will increase stand persistence. Risk of rain damage is less during harvests later in the season and forage quality changes less with maturity then in the spring.

The Minnesota Alfalfa Harvest Alert program

This ongoing program involving on-farm sampling provides information on the changes in alfalfa height and relative forage quality (RFV) and relative forage quality (RFQ) over time so that alfalfa growers can optimize their harvest timing, striking a balance between crop quality and yield potential. Weekly results are available from the Alfalfa Harvest Alert/Scissor Cut Information webpage.

Alfalfa weevils

Alfalfa weevils are a major insect pest of alfalfa that can affect forage yield and quality at both the first and second harvests. Scouting for presence of the insect is the first step in integrated pest management. The alfalfa weevil’s life cycle, its effect on forage yield and quality, and its control will be described in  upcoming Minnesota Crop News articles.