I made an effort this year to seek out and spray colonies of the invasive Crown Vetch. For several years now, I’ve been finding random clumps of this invasive plant scattered about Blue Jay Barrens.
My efforts began last autumn when I mowed several Crown Vetch infested spots in the field. I returned to those spots in April to spray the early season growth. I also targeted early season growth between the township road and my field fence.
I elected to use the chemical Clopyralid as a control agent. Clopyralid is a selective herbicide that targets broadleaf plants, especially legumes. Unlike glyphosate, which kills all green growing plants, Clopyralid leaves grasses unhurt, so the treated area does not become a big bare spot awaiting the arrival of new invasive seeds.
Within a week, the Crown Vetch was showing the effects of the herbicide.
A month after that, all traces of the invasive plant were gone.
The light colored area in the background at the upper left of the photo is the township road that runs along two sides of a large prairie opening. A scattering of Crown Vetch plants, remnants of a government funded planting in the early 1980’s, persisted along the shady lane and produced seed that moved with the rain water to establish new plants along the edge of my field. Hopefully, that influx of seed will now end.
In late May, I found a large infestation of Crown Vetch in a low area that receives runoff water from the road ditches.
The vetch was growing at a rate slightly slower than its companion prairie forbs, making it difficult to see from a distance. Fortunately, I was in the area doing some other work and just blundered into the middle of the Crown Vetch patch. The Clopyralid successfully eliminated the vetch from this site, but it also took most of the other broadleaf plants. That was a bit of a disappointment, but there was plenty of grass left, so the site was not bare.
By late June, the Crown Vetch was blooming. Blooming plants are easy to find and I made sure to search in all places likely to have an infestation.
Crown Vetch is aggressive enough to eliminate all neighboring plants. By using a herbicide that doesn’t result in the elimination of all species, I have left things in better condition than they would have been if left to the mercy of the vetch. Crown Vetch increases its growing area by using a technique known as sprawling. Stalks grow upright by using neighboring plants for support. Eventually, the stalk overtops the other plants and falls over. The fallen stalks form a canopy over surrounding plants, causing those plants to suffer from shading and become less vigorous. The affected vegetation eventually dies and the vetch claims this new growing area. A single patch of Crown Vetch can eventually cover an entire field.
Most of the Crown Vetch clumps covered less than 50 square feet. Only one was over 100 square feet. I’ll have to wait until next growing season to what grows back on the treated sites, but I think the use of Clopyralid has had a positive impact on control of the Blue Jay Barrens Crown Vetch invasion.