When it comes to getting rid of invasive woody plants and weedy perennial grasses in your yard, I know from experience that hand-pulling or repeatedly cutting them back does not work. I find it ironic that a number of these hard-to-control invaders were initially planted as ornamental plants that later "escaped" the confines of the garden.
These invaders include golden bamboo, English ivy, pampas grass (Cortaderia selloana), tree-of-heaven, Virginia creeper, wild blackberry, and poplar, aspen, cottonwood and willow trees. Many of these regrow from their roots or underground stems after cutting them back. In fact, tilling or cutting certain ones back can create more plants and a bigger problem.
If the plants are not too big or if not too numerous to make it impractical, you may want to try digging them out. Do your digging in early spring or late fall after moistening the soil first to make digging easier. Get as much of the root system as possible. Regrowth often occurs from roots left behind.
In many cases, digging out invaders is not an option. Cutting them back or mowing may work, but it must be done repeatedly with vigilance. You might have seen in the news that some cities have hired goat wranglers and their goats to help control woody invaders, such as English ivy and black raspberry, especially in situations where it is extremely difficult to cut or mow. However, goats are probably not a practical option for most gardeners.
Chemical control to kill unwanted woody and grass invaders might be the only realistic and effective option in the home landscape. Luckily, there are chemicals available for the fight against woody weeds and tough grass invaders, but it is extremely important to read and follow label directions to protect yourself and nearby desirable plants.
There are a number of commercial products labeled as "brush killer" for home use. Most contain triclopyr or glyphosate as one of their main ingredients. Glyphosate is a nonselective herbicide that can damage or kill other plants to which it is applied. However, it is not active via uptake through the soil. Triclopyr will kill or damage most broadleaf plants to which it is applied, but it generally is not damaging to grasses. Triclopyr does have some soil activity, so take care not to apply an excess of the material to the soil.
There are two main ways to apply brush killers. Check the product label for guidance. One method is to apply it as a foliar spray to the green leaves of woody weeds. This works best when the plant is actively growing in late summer. Taking care not to get the spray on nontarget plants, wet the leaves thoroughly with the product but stop before it starts dripping off the leaves. If regrowth occurs in the future, apply again when regrowth leaves are fully developed.
A paintbrush is the other method of application. The brush is used to apply the product to freshly cut stumps (trees and shrubs) or stems (vines, grasses, bamboo). This is done when the plants are actively growing and immediately after cutting the plants as close to the ground as possible. When trying to keep a large-diameter tree from regrowing from the roots, apply the material to the outer ring of wood near the bark along with the bark area. If regrowth occurs, spray the leaves when they are fully developed.
Finally, be a good neighbor. Do not use brush killer chemicals to treat sprouts coming from a plant growing on a neighboring lot. The chemical might be taken up and harm the "parent" plant. Your best bet in these situations is to install some type of physical root barrier between your yard and the next. A root barrier can be a solid metal wall, rigid plastic, or synthetic geotextile (landscape fabric) impregnated with herbicide to prevent root growth.
-- Marianne C. Ophardt is a horticulturist for Washington State University Benton County Extension.