Strategies for Weed Control in the Upcoming Season

Fall and early winter is a good time to determine what your alfalfa management practices will be for the coming season. It is important to remember that a full stand of alfalfa (30 stems/sq. ft.) will essentially produce weed-free hay if insects are controlled and soil fertility is maintained. To establish the stem density of alfalfa for a given field, it is suggested to count stems per square foot in at least 20 locations in the field. Do this in the fall when there is good regrowth of alfalfa by counting all of the main stems in each of the 20 - one sq. ft. sampling areas. The average number of main stems then is an estimate of the stem density of the field.   

Since soil diseases are the major factor that contribute to thinning stands, it is critical to plant improved alfalfa varieties with multiple pest resistance. Thus, the foundation of a good weed management program in alfalfa would include; 1) plant a recommended variety, 2) maintain soil fertility, 3) control insects when they reach economic threshold levels, 4) Scout fields routinely to determine alfalfa stem density and weed infestations, and 5) control weeds in thinning alfalfa stands when weeds start competing with the alfalfa.   

The best measure of current competitiveness of your alfalfa stand is how it competed with the weeds this past summer. If there were weeds in your hay this past summer, then there will probably be more weeds in your hay this coming hay season. Cool-season weeds (like downy brome and shepherd's-purse) often become a problem by the 4th year. Once cool-season weeds make up 5 to 10% of the forage at first cutting, then it will usually pay to control these cool-season weeds with a herbicide like Sinbar^® or Velpar^® applied in January or February. Controlling cool-season weeds in the first cutting increases the quality and the "dollar" value of your hay. Results also carry-over to the second cutting, with increased forage yields of as much as 15%.