It’s kill time

By Hay and Forage Grower

After several years of nurturing, fertilizing, and spraying an alfalfa stand to keep it productive, there comes a time when all good fields reach the end of their useful life.

The reasons for alfalfa termination are numerous: low productivity, weed encroachment, previous winter injury, or just a planned rotation move to the next crop.

Agronomists at the University of Minnesota suggest that there are benefits to terminating alfalfa in fall rather than waiting until next spring. They list these advantages as follows:

1. A more effective kill if glyphosate is used, though glyphosate alone does not often provide a complete kill of alfalfa even if sprayed in the fall. Glyphosate, of course, is ineffective on Roundup Ready alfalfa but may be used if perennial grasses have encroached into the stand.

2. If 2,4-D or dicamba-based products are used, there’s less risk of injury to neighboring fields or susceptible border plants compared to spring. Plant-back restrictions are also not an issue as they might be in the spring.

3. A fall kill allows for an earlier planting date in the spring. This might be the most important advantage, as 4 to 6 inches of alfalfa growth are needed before a spring herbicide kill. For crops like corn, delayed planting generally translates to a lower yield.

4. Killing stands in the fall allows more time for the alfalfa residue to decompose and perhaps earlier nitrogen availability for the subsequent crop.

5. If an inadequate kill occurs, spring offers a second chance option.

If tillage alone is used to terminate an alfalfa stand, it must be aggressive enough to sheer roots, but aggressive tillage is not often an option for highly erodible soils.

Herbicides need to be applied before a fall killing freeze and when there is sufficient alfalfa vegetative growth. Ideally, temperatures for a few days following the application should be above 50°F. Often the combination of an herbicide application followed by tillage a week or more later provides the best control.

Base herbicide selection on the composition of the stand. Though growth-regulating herbicides such as 2,4-D and dicamba in combination are very effective for terminating alfalfa, they won't kill perennial grass species. As mentioned earlier, this is when glyphosate must be added to the mixture.