Producers usually experience some winterkill in alfalfa every spring, and 2015 is no exception.
North Dakota State University researcher Marisol Berti recently reported winterkill from Wisconsin to North Dakota, especially in stands 3 or more years old. Newer stands usually are more winter hardy unless soil heaving occurred.
Winterkill of alfalfa is a concern to producers because it is a forage commonly produced for sale as livestock feed. Forage is the foundation of all dairy diets, and the highest-quality alfalfa usually finds its way to the dairy market, NDSU Extension Service dairy specialist J.W. Schroeder says.
A common question from producers experiencing winterkill is, “How do I know if the stand is good enough to keep or I should reseed?”
A stand of alfalfa releases auto-toxic compounds into the soil, inhibiting alfalfa regrowth. How long these compounds remain is based on soil type, temperature, amount of rainfall and the time from tillage to reseeding. These compound residues affect only alfalfa. They will reduce future yield up to 60 percent if reseeded within one year of killing the stand and 15 to 20 percent if reseeded in one to two years on medium to heavy soils.
One option for determining the viability of a stand of alfalfa is to check out a University of Wisconsin Extension publication. The publication, “Alfalfa stand assessment: Is this stand good enough to keep?” is online at http://tinyurl.com/alfalfa3620.
The authors note that when producers are making long-term decisions, they should use stem counts to estimate future yield potential. Assess stand yield potential based on stem densities per square foot as follows:
- Greater than 55 stems indicates density will not be a limiting factor.
- Between 40 and55 stems indicates some yield reduction likely will occur, but fields may be adequate in years of low inventories and high value.
- Fewer than 40 stems indicates a poor stand and the stand should be considered for termination.
“A stand can be slow to recover when injured, but it can recover,” Schroeder says. “Do not be in too much of a hurry to tear it up until you've looked at some roots to determine health.”
If surviving plants are injured but have adequate stem density (40 to 50 stems per square foot), the best option probably is to attempt to maximize production from the existing stand this year, then terminate it after the growing season. If most surviving plants look reasonably healthy (losses were spotty across the field), you might consider inter-seeding a mixture of annual forages and perennial grass forages to stretch the stand beyond this year.
A short-term solution is to plant an annual forage that grows quickly, such as forage oats or oats mixed with forage peas, according to Berti. These annual forages could be ready for harvest by the end of June.
Other options such as inter-seeding with perennial grasses will take considerably more time to establish, and harvest could be delayed until the end of August, depending on the availability of moisture.
Visit with your Extension agent or local agronomist for help in assessing your alfalfa stand.