Last year we completed a small research study on how to kill buckthorn. If you live in the upper Midwest then you’re familiar with this plant as a shrub which has escaped cultivation, been spread by birds, and generally made a nuisance of itself, particularly at the edges of forested land.
Buckthorn is notoriously difficult to kill after it gets more than about a foot high. It laughs at single applications of roundup. If it’s pulled out of the ground any roots that don’t come with it have a good chance of sprouting shoots themselves, and it seems to enjoy being treated with organic herbicides like vinegar. So, to try and kill bucktorn, we used an herbicide which had the active ingredient triclopyr. This is an active ingredient which is usually great against all manner of weedy vines like poison ivy. This herbicide is labeled for homeowner use and is available in most garden centers.
We applied this herbicide to buckthorn in the spring, summer and fall, and we used a few different application methods including painting the herbicide onto cut stumps and spraying it onto the leaves of uncut bushes, as well as painting the product onto the lower portion of stems. Some of these application methods were experimental. Do not attempt to apply an herbicide in any way besides that which is listed on the label!
That said, we found that the fall was by far the best time to apply the herbicide and that spraying the foliage wasn’t nearly as effective as other application methods, particularly painting the cut stem with the product after cutting it down.