Woody Invasive Plant Control in the Fall

Invasive plants are non-native and can reduce economic values, damage the environment, or cause harm to human health. Autumn is a great time to identify and manage invasive plants in your woodland. The yellow foliage, yellow capsules, and bright red berries of oriental bittersweet are easy to spot, and buckthorn trees and other invasive shrubs are easier to locate and identify because their leaves hang on late into the fall without changing color.

Some commonly seen invasive woody plants in Pennsylvania include: tree-of-heaven, buckthorn, Norway maple, callery pear, princess tree, white mulberry, Asian bush honeysuckles, multi-flora rose, Japanese barberry, autumn olive, and privet. For details on these invasive species and more, visit the Pennsylvania Department of Conservation and Natural Resources (DCNR) web site.

While mowing or cutting can be used as a management strategy, most deciduous trees and shrubs will re- sprout vigorously following cutting. Some woody invasive plants like tree-of-heaven can re-sprout from underground lateral roots several feet from the main plant. For effective control, these species must be controlled chemically.

Chemical Control Methods

1. Cut Stump Treatment - Cut the plant near the ground and treat the cut surface (inner bark and sapwood) immediately with a labeled herbicide.

2. Frill Applications (Hack and Squirt) - Use a hatchet or similar device to make frills, or cuts at a downward angle, at proper spacing around stem. Cuts must penetrate into the sapwood. Spray herbicide into cuts.

3. Low Volume Basal Spray - Using an oil carrier and herbicide, thoroughly wet the bark and any exposed roots from ground line up 12 to 18 inches.

4. Foliar Application - Mist the herbicide mixture onto the foliage of targeted plants. Do not spray to the point of runoff. Spray leaves to wet around the entire tree. Avoid spraying non-target plants.

For more detailed information on forest herbicide application methods see the publication entitled: Herbicides and Forest Vegetation Management form Penn State Extension. Always read and follow label directions, wear recommended protective clothing and avoid contact with non-target plants. The label directions will list plants controlled, areas where the herbicide can be used, and application methods. Before purchasing a brush control herbicide, read the label to verify the product is labeled for your site and will control the plants you want to eliminate.

Two of the most successful and commonly used active ingredients include glyphosate and triclopyr. Glyphosate (e.g. Roundup®) is a non-selective herbicide which can injure any green plant. Triclopyr is a selective herbicide active on broadleaf plants. Triclopyr has two formulations: amine, or water base, (e.g. Vastlan formally Garlon 3A) and ester, or oil base (e.g. Garlon 4 Ultra). Even after treatment with an herbicide, re-sprouting and seedling sprouts may continue for years. Monitor sites for re-growth annually and retreat as needed.

Non-Chemical Control Methods

Non-chemical treatment options may vary with species and age of the woody plant.

1. Pulling - Removing the root by pulling is effective when soil moisture is high and plants are small. Success is species specific. Asian bush honeysuckles are relatively shallow rooted and easily pulled. Hand pulling tools are also available (e.g. Weed Wrench and Puller Bear).

2. Cut and Grind Stumps - Stumps should be chipped to below ground level to minimize re-sprouting.

3.Cut and Cover Stumps - Covering stumps with plastic or material that excludes light for two years can reduce sprouting.(Methods 2 & 3 are effective on species that stump sprout. They are not effective on species that sucker or spread from lateral roots.

4. Frequent Mowing - Repeated mowing may control woody broadleaf plants. However, frequent mowing favors grasses which may not provide beneficial habitat for wildlife. Mowing on a 3 year rotation (1/3 of area each year) may be enough to control invasive shrubs and promote native forbs. If large stems exist initially they should be cut by hand and chemically stump treated to prevent re-sprouting.

Equipment

Equipment for controlling undesirable woody plants varies from inexpensive hand tools to large power equipment. Selection of tools will be determined by budgets, size of plants, number of plants, size of the site being managed and who will be doing the work.

Re-Establishing Native Vegetation

Many native tree species can re-establish once undesirable invasive plants are controlled. Desirable plants can also be seeded or transplanted. There are a number of native small trees and shrubs that could be considered to improve wildlife habitat such as; high-bush blueberry, winterberry holly, spicebush, buttonbush, nannyberry viburnum, arrowwood viburnum, crabapple, hawthorn, elderberry, American plum, serviceberry, chokecherry, gray dogwood, American hazelnut, and black chokeberry. In many cases, for plantings and the re-establishment of native vegetation to be successful it will be necessary to reduce the impact of deer through controlled hunting and the use of the DMAP program.

Revised from Woody Vegetation Control, University of Minnesota Extension.