How should Roundup Ready alfalfa be used on your farm?

Recent findings released by MSU provide insight on glyphosate-resistant alfalfa performance.

It’s been four years since glyphosate resistant alfalfa (RR) has been sold to producers. Over that period of time, producers are still asking the same question to researchers, sales professionals and Extension educators concerning whether or not they should plant RR alfalfa. In my experience, the answer is dependent on whether the investment in the technology for RR alfalfa meets the goals of the producer. The potential benefits of Roundup Ready alfalfa include: broad spectrum weed control in either new or old seedings; flexibility in weed control times and selectivity; and excellent crop safety.

A detailed MSU study, designed by Drs. Jim Kells and Rich Leep, was planted in 2003 and compared an established RR alfalfa variety treated with glyphosate, an untreated, and a conventional herbicide (Velpar) treatment. In addition, there was a comparison of management of alfalfa between high intensity (28-day cutting interval) and moderate intensity (35-day cutting interval).

The trial was concluded in 2010 after looking at the effects of harvest frequency and weed removal on RR alfalfa yield, relative forage quality (RFQ), and stand persistence. Note that this study was specifically designed to compare weed management and harvest frequency after establishment. This study did not examine the effect of weed management during alfalfa establishment.

View a fact sheet on the study. 

Observations

  • High harvest intensity (HHI) cutting interval (four to five cuttings per year) yields were higher early in the stand life and lower later in the stand life compared with the moderate intensity (MHI) cutting interval (three to four cuttings per year).
  • There were more weeds in the HHI than the MHI later in the life of the stand.
  • HHI usually had higher RFQ than MHI.
  • Harvest intensity had no measurable effect on stand persistence.
  • Glyphosate and Velpar were both effective in removing weeds.
  • Weed removal had no consistent effect on alfalfa or total forage yield.
  • Weed removal had no consistent effect on RFQ.
  • Weed removal with herbicides had no measurable effect on alfalfa stand persistence.

Conclusions

Based on the above observations, researchers were able to make the following conclusions:

  • HHI resulted in higher RFQ, but yield declined more rapidly over time.
  • Harvest intensity did not affect stand persistence.
  • Weed invasion was generally more rapid with the HHI system.
  • Glyphosate and Velpar effectively removed weeds from established alfalfa, without generally affecting yield or quality.
  • Weed removal with herbicides did not affect stand persistence.

The question remains about whether the use of herbicides on an established field will help the alfalfa stand stay in production longer. 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.

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