Invasive Shrub Control

The exotic shrubs that plague Pennsylvania including multiflora rose, autumn olive, shrub honeysuckle, and Japanese barberry among others, are not difficult to control. They are prolific and quite numerous, but compared to other plant growth types, they are not hard to kill. Click here to watch a short video entitled Invasive Shrub Control Strategies.

None of the problem shrubs are suckering or root sprouting species. This means, if you effectively treat the top of the plant and kill the stem tissue, the roots will die. This also allows for more flexibility in timing treatments. Because they leaf-out early and drop their foliage late compared to most native woody species, there is a longer operational window to manage invasive shrubs compared to rhizomatous or root-creeping species. Foliar treatments are an option for most exotic shrub species from June into October while stem and stump treatments can be done year-round, weather permitting

Small infestations of young plants, particularly shrub honeysuckles and privets, can be effectively pulled by hand. For larger stems and infestations mowing is often the first approach. It effectively removes the shrub canopy, and eliminates the need to drag and chip or burn the stems after cutting.

There is a wide array of brush cutting machines available. Smaller stems are readily dispensed with heavy-duty rotary or flail cutters (i.e., 'brush hogs'). For larger stems, fixed-tooth, drum-type forestry cutters not only have the capacity to cut down large stems to the ground line, but also finely chop the debris.

Mowing is not a standalone treatment. To be effective, mowing must be followed with a fall (or next growing season) herbicide application to eliminate resprouts. Selectively treating knee-to-waist high resprouts with a backpack sprayer is a relatively quick process. When foliar-treating resprouts be sure to distinguish invasive species from native look a-likes such as viburnums and dogwoods you wish to release on the site.

Herbicide foliar "spot" treatments with a backpack sprayer are an effective means to treat sites with low to moderate shrub density. Typically, several shrub species will be present on a site. Using a mixture of the herbicides glyphosate and triclopyr will provide a broader spectrum of control than either product alone (See invasive plant information). This mix is non-selective, meaning it controls all plant types that it's applied to. However, this mixture poses no risk to untreated desirable plants through root uptake, because these active ingredients are not soil-active at the dosages used in foliar applications. Be sure to calibrate your sprayer to achieve the desired dosage.

Stem treatments include basal bark and stump treatments. They can be applied throughout the year, providing scheduling flexibility. Basal bark treatment uses a concentrated mixture of the herbicide triclopyr-ester in a basal oil. It is applied to the entire circumference of the lower 12 to 15 inches of the intact stems. Some triclopyr-ester herbicides come premixed and are ready to use right out of the container.

If you want to remove the top growth of shrubs, the preferred approach would be cutting the stems close to the soil line and treating the stump to prevent resprouting. Oil-based triclopyr-ester herbicides can be applied any time after cutting and should be applied to the cut surface as well as the sides of the stump, while water-based herbicides using glyphosate or triclopyr-salt should be applied immediately to the freshly cut surfaces.

When prioritizing work, consider working in the least-invaded areas first. In other words, focus on sites with native vegetation that you are releasing first, then move to sites completely overrun with invasive shrubs. Think in terms of maximizing "Acres Protected" when working, to optimize productivity and ecological benefit.

Treated sites must be maintained through periodic re-treatments since some invasive shrubs will be missed or may regrow from seed following treatment. New plants will continually invade sites as birds and other wildlife carry in seeds. Invasive shrubs are kept under control only through a continued maintenance program.