Killing Invasive Vines such as Kudzu, Oriental Bittersweet, Mile-a-Minute
Invasive vines can really take over. They primarily crowd out desirable species by shading them, but they can also girdle stems of desirable plants and cut off the free flow of plant sugars to the canopy.
To control them with herbicide, there are several things to keep in mind. First, a foliar application to vine foliage is almost always a bad idea. Usually the foliage of the vine is too intermingled with the foliage of desirable plants. Even if you can segregate the foliage of the invasive from the desirable, spraying upward where vines grow is inadvisable. You will likely end up with more spray mist on yourself than on the target vine.
Second, don’t pull the vine down from the canopy. If you do, you may do more damage to the desirable plant by breaking branches and tearing into live plant tissue (if the vine has adhesive pads that attach to stems). Focus your efforts instead on killing the vine and leaving it in place. If you want to speed its decay and to lessen strangulation of a desirable plant, cut notches into the vine stem. Again, avoid cutting the desirable plant.
Third, you will probably have better luck killing the vine if you apply the herbicide in late summer, fall, or even winter. Those are the times when the plant is translocating sugars to the roots which is also where you want the herbicide to flow.
If you want to prevent the vine from producing seeds, here is a trick that I use. After the vine has leafed out but well before it has produced fruit or seeds, cut the vine as high as you can from where it is rooted. Then allow the vine to regrow. It probably will do so vigorously with multiple new sprouts from near the cut. The trick is that you will do your treatment below this cut and new sprouts. This not only should prevent the vine from flowering and producing seeds, it will also sap the roots of energy and make the herbicide application more effective.
One way to apply herbicide is to use what is called a cut stump method (shown above). With this method, you cut the stem of the vine close to the ground – generally two to four inches above the ground from where the vine is rooted. (if the vine is rooted in multiple locations, you will need to cut and treat near each root clump.) Don’t cut so close to the ground that dirt gets on the cut face of the stump (dirt neutralizes herbicides such as glyphosate). But don’t cut too high because the treatment will be less effective. Then immediately treat the stump face with a concentrated foam herbicide. Apply the foam herbicide in a ring near the outer perimeter. You want to make sure the herbicide contacts the living plant tissue called the cambium which is just inside the outer bark. Green Shoots Foam Herbicide works great for this because you can precisely stack the foam right on the cambium and it will slowly soak in. If you wait more than about 10 to 15 minutes after cutting the stump, I would recommend re-cutting before applying the herbicide. Plants seal off wounds surprisingly quickly and this reduces the effectiveness of the herbicide. Follow the instructions on the label for the herbicide and the dispenser.
Another method is a frill treatment. With this method, you scrape or cut away some of the outer bark to expose live, inner bark as shown in the photos above. This method work especially well if the vine stem is horizontal because it provides a better surface on which to apply the herbicide. If you can try to remove bark from around the perimeter of the stem. Again, Green Shoots Foam Herbicide works great for this because the foam will cling to the frilled tissue. (Liquid herbicides on the other hand will drip right off.)
Be sure not to get herbicide on desirable plants. I even avoid getting herbicide on the outer bark of desirable plants. Although you may read that water-based herbicides won’t penetrate the protective, waxy layers of cork, it makes sense not to risk harm.