15 Mar Evaluating Your Alfalfa Stand
March has certainly come in like a lion this year! The winter brought above average precipitation in the form of snow in many areas across the USA. Our winter precipitation may continue as rain during spring if current weather patterns are any indication. What does all this mean for over-wintering alfalfa stands?
Snow cover on over-wintering alfalfa stands is a good thing. Snow provides insulation from extreme cold temperatures, protecting alfalfa crowns during the winter dormancy period. Soil temperature under snow cover generally remains in a range that allows winter survival.
Environmental conditions during spring green-up can impact stand survival. Take time to check your alfalfa stands during spring green-up to insure continuing productivity. A sparse alfalfa stand allows weed encroachment and negatively impacts yields no matter what herbicide program you use.
But what happens when all that snow melts? The moisture from melting snow can evaporate, or seep into the soil, or cause run-off. When rain falls on snow, the resulting runoff can exceed that from rain or snowmelt alone.
The ideal spring thaw would have March going out like a lamb, with a gradual steady rise in daily temperatures that allows for gradual snow melt. If all goes according to plan, your spring thaw will be uneventful and your overwintering alfalfa will come on strong for a high-yielding first cut. But reality is sometimes different, and experience tells us to pay attention to alfalfa stands as spring thaw gets underway, given the possibility of late freezing, ice sheeting, and prolonged ponding or even flooding.**
How will you decide about whether to keep a damaged or older stand? Most alfalfa growers are familiar with stem counts as a way to evaluate alfalfa stand productivity potential during the growing season. But stem counts are not possible until overwintering stands green up in spring.
You can make a preliminary assessment of alfalfa stand productivity before spring green-up, by counting plants per square foot in several areas of the field. Dig plants to assess whether crowns and roots are a healthy off-white color, not dried out, and not diseased. Assuming healthy plants, count plants per square foot while you’re at it.
Stands that were newly seeded in mid-late summer 2022 should come out of winter with 20 or more plants per square foot with good uniformity across the field. For established stands planted last spring you should have at least twelve plants per square foot. Look for greater than 8 healthy plants per square foot in the spring of the second year, and at least 5 per square foot by the spring of the third full year after establishment.
** Here are some good references for the main environmental challenges that alfalfa may face during spring green-up:
Alfalfa Frost Heaving: Assessing the Damage (psu.edu)
Alfalfa winter injury assessment and management (umn.edu)
Effects of Late Spring Frost on Alfalfa (sdstate.edu)
Heaving in Alfalfa Fields – Integrated Pest and Crop Management – UW–Madison (wisc.edu)
Ice on Alfalfa – Team Forage (wisc.edu)
Managing Flooded Alfalfa (sdstate.edu)
When alfalfa winterkills, what can you do? – Forages (msu.edu)