UPDATE For a full list of herbicides registered for use in sainfoin, see this post: Herbicides for sainfoin
Sainfoin is being promoted by a variety of sources as a good forage alternative to alfalfa. It has many desirable attributes: it has high nutritional content, it seems well adapted to Wyoming (particularly northern Wyoming), and it does not cause bloat so it can be grazed. The University of Wyoming has released 2 varieties of sainfoin that are well adapted to the area: ‘Shoshone’ and ‘Delaney’. There is a lot of interest in the crop, and many researchers across the region are promoting the crop. However, even as sainfoin acres increase, there is one glaring absence from nearly all of the management recommendations for establishing and managing sainfoin: How do we manage weeds in sainfoin?
One of the most common questions I get about sainfoin is whether there are any herbicides that can be used to control weeds after sainfoin establishment. An extension bulletin from Montana State University states: “Weed competition can be reduced in the seedling year by mowing, grazing, or with herbicides.” However, no herbicides are mentioned in the bulletin. Clethodim (Select) and sethoxydim (Poast) are registered for use postemergence in sainfoin to control grass weeds. Other than that, postemergence options are extremely limited… in fact I’m not aware of any other herbicides that are labeled for use postemergence on sainfoin (please feel free to let us know in the comments if you know of any).
Even though there are few (or no) herbicides registered for use once the sainfoin is established, one herbicide option that continues to surface in discussions is glyphosate (active ingredient in Roundup). In fact there are a number of resources on the web that are actually recommending the use of glyphosate for weed control in established sainfoin:
- “Sainfoin is already naturally resistant to Roundup and many chemicals“
- “I hit it with six ounces of Roundup in the spring to keep it clean“
- “Roundup Resistant, spray 4-6 ounces per acre on new seeding, 8-12 ounces as needed every year after that“
I have also heard many anecdotal reports from growers and researchers that have used glyphosate on sainfoin with little or no observable injury. The concerning issue for me is that there is almost no evidence from replicated research trials indicating that glyphosate can be safely used on sainfoin. The only peer-reviewed research on the subject of glyphosate in established sainfoin inexplicably did not collect any forage or seed yield data, which makes it of very limited value.
In the fall of 2011, a trial was established at the Powell R&E Center to screen sainfoin tolerance to various herbicides. Several rates of Roundup were included, in order to finally quantify the effect of glyphosate on sainfoin yield. This photo was taken approximately 2 weeks after Roundup PowerMax was applied at a rate of 12 fluid ounces per acre. The plot in front shows the Roundup treatment, compared to healthy sanfoin directly behind it. Even though there are many accounts of glyphosate being safely used in sainfoin, this illustrates the potential crop injury that can result. Based on the information obtained so far from this trial, I would strongly recommend against spraying glyphsoate (at any rate) in a growing sainfoin crop. Yield data will be collected from this trial and will be made available as it is collected.