By Bill Kleiman
Nachusa Grasslands has a 20-acre prairie planting, number 91, http://www.nachusagrasslands.org/uploads/5/8/4/6/58466593/planting_91_-_2009_-_stone_barn_prairie_-_stone_barn_farm_unit_-_crew_-_c_considine.pdf that is coming along nicely with a thick cover of native plant diversity. But it also has about 100 birdsfoot trefoil, Lotus corniculatus, small patches of plants scattered throughout.
I used the little tractor above with its 50 gallon tank to drive transects back and forth across the planting to find the trefoil. I did not use the boomless tip but rather a hand nozzle where I can spray almost as exactly as a backpack sprayer can. The tractor is nice for this purpose because it is nimble, you sit higher than in a UTV, and it is easy to go slow and look.
Why would I use a tractor instead of going on foot? I had about two hours to spare, the unit had not been burned so it was harder to walk through. The crew was busy with trefoil on another unit. So I loaded with 1 ounce per gallon Milestone (this is less than one percent and more than half percent) and non-ionic surfactant and drove slowly along.
My error, the miss, is that I should have done this work a week earlier because now about half the trefoil looked as above with seed pods forming. Those brown ones are full of seed mature enough to seed the ground. From experience, trefoil seeds last for a decade or two in the soil. This cohort of seeds will germinate not all at once, but they will emerge at various times in the summer and for many future summers. These are good traits for a plant picked to deal with heavy grazing.
Let us not dwell on why the Federal government is breeding this weed to be even more aggressive while also funding natural areas work to control it.
The trefoil got in there because a nearby degraded remnant has patches of trefoil. Likely deer and rabbits deposit seed in the planting.
I could not let the seed go. A few days later I went out three mornings in a row to re-locate the patches I sprayed (easy to do as I just followed the tractor tracks with my UTV). I tried clipping the plants with a scissors and I tried using a scythe to cut the entire plant, but I ended up concluding (with my daughter’s help) that simply tearing at the trefoil by hand worked fastest. I filled up 28 barrels with trefoil and added it to weed burn pile.
I also sprayed a bit of basal bark herbicide where the plants emerge for good measure. I covered this topic here: https://grasslandrestorationnetwork.org/tag/lotus-corniculatus/
Lesson learned: Don’t be late. Have a method to remind you where weeds are located. We use Field Maps (formerly Collector). Have a calendar warning. Don’t plant prairie into soils with weed issues. Don’t let legume weeds go to seed. If you create nice prairie plantings you won’t mind defending them from invasive weeds.
grassland restoration network 
I’ve been battling Trefoil on a smaller prairie and other parts of our property for at least ten years. I’ve managed to clear it out in some sections, but it persists in others. I’ve used a variety of methods. I hand-treat as many as possible (with Transline/Stinger on sponge-loaded tongs or using a hand sprayer) that emerge after spring burns. This gets much more challenging as vegetation fills in and the remaining plants get larger. I have also used Garlon on the stems near the root if I can get to it (the late-Tom Brock described this method a few years ago). And sometimes you just have to pull them. In the fall, it can get a little easier to get at the plants as other vegetation dies back. In non-prairie areas, I’ve sprayed with Stinger every few weeks, but new plants keep popping up through the summer, and they’re always back in the spring. I’ve always thought that Trefoil spreads primarily through rhizomes rather than seeds, but I really don’t know whether this is true. But it sure keeps me busy!
Thank you, Bill. I always enjoy learning from your experiments and experience.
I have a question; if you are using Milestone at 1% v/v (38 mL per gallon), at a maximum label rate of 14 oz/acre per partial area coverage, 1% would only be an application rate of 11 gallons spray per acre. Did you perhaps mean 0.1% Milestone? I’ve been using Milestone for a long time, usually at 2 to 8 mL per gallon (0.053% – 0.21%), for spot spraying, with good results.
Also, is MSO the best ajuvant to use on this herbicide? I didn’t see MSO listed in the label and I thought that an NIS adjuvant was most recommended.
Thank you again, Bill
Nathan, Thanks for commenting. I used non-ionic surfactant. I wrote MSO by error. Thanks for the catch. I was just re-reading the Milestone label and puzzling what rate a spot spray should be. The last several years I was using one ounce per gallon, not 1% (which is 1.25 ounces per gallon). Lately I made a 1% solution because I remembered it wrong. 1/2% equals 0.63 ounces per gallon. 1% equals 1.25 ounces per gallon. I called colleague Bryon Walters who got a recommendation from another colleague of 1/2% solution Milestone. It is hard to figure out the conversion of the label rates for use in a boom sprayer to a backpack spot spraying. Less saves money if it works.
Bill, thank you for for clarifying this information.