Glyphosate and a conventional herbicide both were effective at removing weeds from established Roundup Ready alfalfa in a Michigan State University study. But weed removal had little effect on yield, quality or stand persistence, reports Phil Kaatz, Extension forage educator at the university.
Kaatz says the study, designed by Michigan State weed scientist Jim Kells and forage agronomist Rich Leep, compared a Roundup Ready alfalfa variety treated with glyphosate, an untreated stand and a conventional herbicide (Velpar) treatment. In addition, high-intensity (28-day cutting interval) management was compared to moderate-intensity (35-day cutting interval) management.
The alfalfa was seeded in 2003 and the trial concluded in 2010. Kaatz emphasizes that it was specifically designed to compare weed management and harvest frequency after establishment, and didn’t evaluate the effect of weed control during alfalfa establishment.
“The question remains about whether the use of herbicides on an established field will help the alfalfa stand stay in production longer,” says Kaatz. “It’s the classic question of which came first, the weeds to decrease the stand life or the plant stand decreasing, letting more weeds into the field? The implication is that continuous weed removal from established alfalfa will probably not increase the productive life of the stand.”