Winter damage to alfalfa is “widespread,” in the state, according to Iowa State University Extension Field Agronomist Virgil Schmitt. “I don’t have a good feeling about the percent of acres that are in bad shape. It is field-wide in some cases, just in spots in other cases and there is no injury in still other cases.”
According to an Extension release on the issue, co-authored by Schmitt, older stands, stands that were harvested between mid-September and late October and stands with minimal stubble appear to have suffered the worst winter injury.
Extension agronomists noted overwinter alfalfa damage has been observed in the following circumstances:
Low spots: Alfalfa does not tolerate wet soils for too long, so some stand loss often is apparent in low areas. With a wet fall and a wet start to the spring between snowmelt and rain, it’s not surprising to see this.
Heaving: The very wet fall conditions and full soil moisture profiles going into the winter also enhanced the chance for frost-heave injury to alfalfa.
Cold temperature exposure: In some cases, the crown/upper taproot couldn’t tolerate exposure to cold temperatures. Very wet fall soil conditions contribute to alfalfa not hardening down as well as usual into the winter. Consequently, the alfalfa’s cold-tolerance is a bit less than normal.
Alfalfa stubble height: Many of the fields with winter-injury are fields without good fall stubble. Both cold injury to plants and heaving damage are more prevalent in fields that were cut short late in the fall.
In response to these conditions, Extension suggested reseeding in hayfields or pastures might be needed.
“It is not recommended to reseed alfalfa into stands that are two years or older due to the likelihood of autotoxicity,” the release stated. “Overseeding or drilling grasses or red clover into thin or winter damaged stands should be done before May 1. Seeding after mid-May increases the likelihood seeds will germinate, but less frequent rainfall will allow the soil to dry out before roots are deep enough to reach moist soil, killing the seedlings.”