A simple experiment on birdsfoot trefoil

by Bill Kleiman, Nachusa Grasslands, TNC

I often carry in my truck a spray bottle of herbicide that is 20% garlon 4 in mineral oil, a basal bark herbicide.  I use this on various brush I see during the summer.  Last year, while cruising for weeds,  I found a few dozen herbaceous invasive plants, birdsfoot trefoil (Lotus corniculatus).  Ordinarily I would spray them with a water based foliar herbicide, perhaps Garlon 3A or Crossbow.  But I did not have those with me.  I just had the basal bark mix.

I know if I sprayed the foliage of the plant with the basal bark mix it would kill it.  But that would be an expensive treatment.  But, what if I just sprayed a small spot, an inch or two wide, at the base of these big sprawling plants?  Would that kill them or just brown them out and leave the root alive?  How would I know if the plant roots died?

I came up with a simple experiment.

Below is my sprayer with basal bark mix and a Lotus plant flagged with blue tape.

Below is a big Lotus plant which I have just sprayed a small circle in the middle of the plant where the stems go to earth.    A complass plant leaf is at bottom.

Below is another Lotus a few days after spraying basal bark in the center.  In this specimen I gathered the stems up to find that center and then applied a small amount of basal bark mix close to the earth.  You can see the plant wilted.  Is it dead?  Note the aluminum tag I applied to a twisted end of wire that that is about 15 inches high.   How will I know I killed the root?  When I return a year later, find this tag, and find no living Lotus there.  The tag is prairie fire proof.

Below is one dead Lotus the next summer.  Therefore, the basal bark mix killed the root.

I tagged about 40 Lotus plants this way but since Covid cancelled our fire season I could only find 10 marked plants in all that un-burned foliage.  But ten out of ten Lotus, birdsfoot trefoil, were dead.

Lessons learned:

These casual small scale experiments are fun to do.  They give me comfort knowing my techniques are working.  They are not large scale enough to publish in a journal, but these experiments help me make a pitch to University researchers to do similar studies at scale with a control.

I should have used taller wires so I could find them all.  I only found one in four tags.

Follow up questions I have:

It is subtle, but I think I see a few inches of sparse vegetation around where the Lotus was.  Is that the Garlon 4 vaporizing and killing plants nearby?  Or had the competition of the large Lotus plants thinned nearby plants?  If I had burned the site I could have had a clearer view of the situation.

What if I repeated that experiment using concentrated glyphosate herbicide on just a center spot?

Other questions on foliar spraying come to mind:

What if I sprayed with water based broadleaf herbicide, but only sprayed the middle half of the plant?  Is that enough to kill it?  What about a quarter of the plant?

What if set up a series of tests of various broadleaf herbicides to see which had the best control of Lotus, but also the least off target damage?

Kudos to Mary Vieregg.  The prairie planting where I did this experiment was created in 2008 by volunteer steward, Mary Vieregg.  She and husband Jim picked and planted all the seed, and weeded if for years after.

The Vieregg planting at Clear Creek Knolls of Nachusa Grasslands.

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4 Responses to A simple experiment on birdsfoot trefoil

  1. Becky Janopoulos says:

    Haha! That’s so interesting because I tried the same thing with triclopyr 3 that I had on me. I spread the plant to find the middle and smashed the stems with my foot a little since my mixture was not an ester ( in my mind I could rough up the stems so they could uptake the herbicide like scratch and squirt) I did this 3 days ago and have to go back and check. I have been battling BFT for YEARS. The good news is my Prairie is mostly a jungle of large species so BFT cannot compete. Its the shorter drier parts of my prairies that have the most BFT. Thanks for the post!

  2. Mary Ochsenschlager says:

    I was wondering if you think the brown on adjacent species could be herbicide movement through the soil and the fact that gallon persists?

    • Mary, I don’t know. I think a herbicide moving from one root system across the soil to another seems less likely than the vapor I can smell when I apply the herbicide. We have a study in mind where we apply basal bark herbicide to woody stems, and then cover the stems up with aluminum foil to cut the vaporization off the bark. If we did this would the wilt of nearby plants go away?

  3. James McGee says:

    Having a plant not return a year after herbicide treatment does not always mean it is dead. The below experience is a good example. Thladiantha was sprayed. The invasive species specialists did not see any the following year. No subsequent monitoring was done. Years later when it was noticed again an entire ravine was infested.

    https://www.minnesotawildflowers.info/flower/red-hailstone

    Herbicide blocks biochemical pathways which prevent growth. If a plant has enough food reserves to survive until the herbicide degrades, then it can begin to grow again even if more than a year has passed.

    My park district foliar sprays crown vetch and bird’s-foot trefoil with Transline every year. The next year they are always back right where they were before. Although, bird’s-foot trefoil does not have a large root, so the ones you treated with Garlon 4 are probably dead. You could probably get the same success from applying a much smaller amount of Garlon 4 active ingredient.

    When these experiments are done, the plants should not only be marked with tags. A map drawn in a notebook should be created. This map should be able to provide direction and distance from landmarks and other tags. I like to use paces as a measure of distance. This will get you within a few feet of each tag which will make them easier to find.

    I use my NRG Pro weeder to remove bird’s foot trefoil. I use a small half log as a fulcrum to lift out the entire root while limiting soil compaction. It’s hard work if you remove hundreds in a day. If you are only removing forty, it should take about an hour and twenty minutes. I don’t have to worry about impacts from herbicide to adjacent species. I save the herbicide for things that are too hard to surgically remove from soil like bush honeysuckles and buckthorns over ¾ inch in diameter.

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