When it comes to killing woody invasive plants, winter is generally the best time. This may surprise you. Herbicide labels may confuse you because labels often say the herbicide should be used when the target weed is “actively growing.”
However, cut stump and basal bark treatments work great in winter as long as the plant has an above-ground stem with live inner tissue. Weed trees and bushes all have live inner bark – the cambium layer. Therefore consider winter treatment for invasive woody species such as Asian bittersweet, buckthorn, honeysuckle, kudzu, privet, tree-of-heaven, etc.
There are a number of advantages to working in winter (or late fall):
- Effectiveness: The greatest success I have had controlling woody species is in late fall, winter, or very early spring (before sap starts flowing up the stem to the branches). This is true for others too. Reinartz 2002.
- Ease of Movement: The absence of leaves and growing plants makes it surprisingly easy to move through dense growth.
- Comfort: Removing invasives can be a lot of work, especially if you use hand tools. You can stay warm without being sweaty and uncomfortable.
- No Mosquitoes or Ticks: This is a godsend. If it’s above freezing and there’s no snow, ticks can be out but at very reduced numbers.
- Identification of Targets: As long as you can identify the invasive by the bark and structure of the plant, Identification is much easier. Without leaves blocking your view, you can see so much better.
- Cold Temps: I usually do not work when it’s below about 20 degrees F. If it gets below that temperature, water-based herbicides may freeze, especially around the nozzle. Plastic containers also become more fragile.
- Deep Snow: It is difficult to do either cut stump or basal bark treatments if the snow is more than a few inches deep. You can remove snow around the base, but this can be time-consuming.
For cut stump treatments, cut the stump as close to the ground as possible (1 to 2 inches) above ground level. (I find that failed cut stump treatments often result from cutting the stump too high.) Brush off any debris on the stump face. (Dirt will neutralize herbicides such as glyphosate.) Then apply the herbicide immediately after cutting (within 5 minutes or so).
Good luck! I hope you are able to get out on a nice warm winter day to remove some invasive plants. It can really be enjoyable!
I remind people every year that fall is a great time to apply herbicides to kill perennial invasive plants. I discussed autumn herbicide applications in a post last year. So, get out and enjoy that cooler weather and, for those of us farther north, beautiful fall colors!
In terms of priority, I would put perennial weeds into three groups: First are the perennials that need to be treated before a frost. Plants such as Japanese knotweed quickly die back after a frost. Therefore they need to be treated in early fall.
Second are the plants such as perennial thistles. Canada thistle is a prime target. Canada thistle can be treated a little later in the fall because it is more frost tolerant. In fact, this frost tolerance can be used to your advantage. If nearby desirable plants have lost their leaves, you can apply herbicide to the thistle with less potential for damage to the desirable plants. Just make sure you apply the herbicide to foliage that is still green.
Third are the woody perennial weeds. These can be treated from the fall into late winter (just do it before warm temperatures start pushing plant sugars up to the branches for leaf out). The application should be into the vascular system of the tree or shrub, e.g., cut stump, frill, or injection. The Directions for the Green Shoots Foam Herbicide System show how to do these applications.