Control Perennial Weeds Before Seeding Alfalfa

Warren C. Thompson National Forage Specialist: America’s Alfalfa

I wonder how many times have I have seen what I thought was a beautiful field of alfalfa from a distance. But on close examination, I find to my disgust and the grower’s disappointment, a lot of seedling weeds just emerging. In many of these cases, the weeds are perennial and we know there are problems ahead. The population could crowd early alfalfa and are sure to reduce the quality of the hay or grazing forage in the future. 

These weeds, especially the broadleaf weeds are almost impossible to control once the alfalfa is up and going. For the most part, the same herbicides that kill broadleaf weeds will also kill alfalfa. In that case, the only option for control is mowing.

In conventional seeding operations, controlling these weeds becomes a more simplified process so long as the problem is anticipated by past history of the field. In recent years, an increasing number of farmers are seeding alfalfa no-till either following row crops or into cool season grass pastures. Unless measures to control seed production of these weeds well ahead of seeding and measures are used to bring them under control, forget it. A little later, we will get into no-till seeding more and try to lead you in the right direction when you do seed this way.

Some examples of tough weeds to control are dock, horse nettle, and the various thistles. There are others that may be native to your area and many are termed biennials. They are tough to control as well after seeding. How do you control them ahead of seeding? It could mean the delaying the planting for a year of row cropping and tillage. In any case, I am going to suggest that you contact your County Agent or your Extension Weeds Specialists at your University to get specific recommendations for your situation if you are especially concerned about hard to control weeds that are native to your farm. The reason I do this is two fold: I cannot possibly keep up with the recommendations in all states and recommendations do change when new herbicides are released. Just be warned, if you have the weeds before you plant, the contamination will get worse, not better.

Don’t overlook pre-emergence sprays as a possibility. The materials that are usually recommended in this program often cause early stunting but the plants usually grow out of this with time. There are two maybe three chemicals that will work for you for control of annual weeds.

In recent years, annual grassy-weed control such as crabgrass, fall panicum, and foxtails have become a lot easier to control with the release of some fantastic herbicides. These are applied directly to the newly seeded or even established stands of alfalfa. Your County Agent has your state’s recommendations. The best weed control however is diagnosis and prevention before planting. Clean up before the alfalfa comes up!