Competition Between Barnyardgrass and Alfalfa 1

Competition between barnyardgrass and alfalfa grown together was studied in 1963 and 1965. Barnyardgrass was seeded semi‐monthly in first year alfalfa stands growing in rows 12 inches and 6 inches apart. Barnyardgrass emerging up to 16 days later than alfalfa significantly decreased alfalfa yields of the first cutting. After mowing, alfalfa as well as barnyardgrass regrew and competition continued. Weed seedlings that emerged prior to 2 weeks before the first mowing of alfalfa decreased yields of the second cutting. The nature of competition in alfalfa seeded 12 inches or 6 inches apart followed the same pattern. The competition was found to be reciprocal—both species competed with each other. Alfalfa seedlings, suppressed but not killed due to the competition by weeds, regained normal growth the following year. It is important to control barnyardgrass seedlings in the year of alfalfa establishment up to the time of the first mowing.