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!
You have an unwanted tree growing vigorously in the wrong place – in the middle of a flower bed or in a native grass planting or next to a building foundation. You know you need to remove it. Winter is actually a great time of year to do this. Herbicides work fine in the winter if applied correctly. See Reinartz 2002.
If you simply cut the tree or bush down, you will soon get something far worse in the spring: a multi-stemmed bush like the one shown below on the right side.
There is a simple way to prevent this from happening: use the Green Shoots Foam Herbicide System to precisely apply a concentrated herbicide to the stump immediately after cutting to kill the stump. So here is what you do.
- Cut back the tree or bush – If it is a big tree or bush, I typically cut off the upper branches first and leave a tall stump anywhere from knee to shoulder height. Clear out the branches so you have room to work.
- Prepare the Foam Herbicide Dispenser according to the instructions. Be sure to read the herbicide label.
- Cut the stump close to the ground – try to cut it within 2 to 4 inches of ground level.
- Immediately apply the foam herbicide to the cambium layer of the stump. This is a thin layer of live inner bark just inside the outer bark.
The Green Shoots Foam Herbicide System has several advantages over standard herbicide sprays:
- Precision – This is critical when you are applying to the narrow ring of live inner bark less than 1/10 inch thick. With a liquid spray, the application is so imprecise – you may miss your target. At the very least, you will waste herbicide trying to hit the target.
- Less Drip – The foam herbicide sticks to the target and will slowly soak in. Liquid sprays will bead and drip off the target.
- Visibility – the foam is visible for some time after the application. This helps in identifying what part of the target you have treated.
For more information about the Green Shoots Foam Herbicide System, visit the Green Shoots website.
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.
Fall is generally the best time to control perennial weeds. Perennials are moving sugars from above-ground sinks – in particular foliage – to underground sinks – rhizomes and roots, for example. for overwintering. In order to kill perennial weeds, these underground sinks must be destroyed.
Fall offers other benefits as well – cooler weather, less dense foliage, and fewer bugs!
What is the best way to kill invasive perennials? Several rules hold. Apply herbicide only to living tissue. Perhaps that’s obvious. That can be green leaves or stems or vascular tissue.
Since most people are probably least familiar with vascular treatment methods, I will discuss those. Photos above show each of these methods step-by-step. One method is to do a cut stump application. With this method a weed tree is cut down and herbicide is applied to the cut-surface of the stump. For most homeowners who used water-based herbicides, you should apply the herbicide soon after the cut is made. (There is debate about how soon but I try to do it within a few minutes if possible.) Two keys to this method are: first, make the cut as close to the ground as possible (e.g., 2 to 3 inches if possible); second, make sure you apply herbicide to the outer edge of the stump just inside the bark. This will ensure herbicide gets introduced into the phloem which will carry the herbicide into the root system. The Green Shoots foam herbicide system works great with this method because the foam stays on the cut-surface and doesn’t drip down the sides of the stump.
Another method is a frill application where the tree is left standing and cuts are made into the bark of the tree. Use a knife or chisel on smaller trees and a hatchet on larger trees to make the cuts. Apply herbicide to the exposed vascular tissue. These cuts should be made as close to the ground as possible. Of the two methods, I find the cut-stump method to be the most effective. However, the frill method probably takes less work especially when you are dealing with big trees.
For green-stemmed perennial weeds, I use a slightly different method. I bend the stem near the ground and apply the herbicide at the bend. For some reason, this method works better than just cutting off the stem. I don’t know why. The Green Shoots foam herbicide system works especially well with this method because the foam sticks tightly to the bend in the stem unlike methods that use liquid herbicide. This technique can be often be used even after the leaves are nipped by frost as long as the stem is still green.
For all these methods, use a concentrated herbicide mixture. For example, if I am using a glyphosate-based herbicide, I typically use a concentration of about 35 % active ingredient.
There are a number of benefits to these methods of application. First, they are very effective. I typically have a 100% kill-rate using the Green Shoots foam herbicide system with these methods. Second, they protect the environment. The methods allow for very targeted applications. And with Green Shoots foam, the herbicide sticks well to the target surface and very little drifts through the air or drips off onto other plants.