Weed Management

Weeds can reduce the growth rate and affect the health of trees and shrubs you plant, as they compete for nutrients, water, and light. On this page, you’ll find information on weed management and control of trees and shrubs, including mulching, herbicides, and pesticides. Find specific tips on dealing with Japanese barberry, mulberry weed, ragweed, sowthistle, knotweeds, and more.

Weed Control and Management for Trees and Shrubs

Whether you’re a green industry professional or growing trees and shrubs in your own garden, managing weeds is essential if you want your trees and shrubs to be healthy. Successful weed control and management require a combination of cultural and preventative measures. You can supplement these measures with the effective use of appropriate herbicides.

One very common method for suppressing weeds is to apply a mulch. Mulch can also enhance the beauty of the landscape, conserve soil moisture, and act as a buffer from the damaging effects of traffic and lawn equipment. Mulching plays a key role in organic land care best management practices.

Proper mulching is one of the best ways to promote vigorous root growth and tree health because it mimics the natural environment found in forests. However, excessive or improperly applied mulch can adversely affect plants. Learning how to properly mulch your trees and shrubs is therefore essential.

Identifying Invasive Plants

When you’re looking for plants to add to your garden, avoid anything on the Pennsylvania invasive plant list. Many invasive plants have lovely flowers, make an excellent color contrast, or you’ll find them being sold at a bargain price. Be aware, however, that they spread quickly because they’re not limited by pests, diseases, or predators. They also grow and reproduce rapidly and thrive in a variety of conditions.

Some of the most common invasive plants are:

• Tree-of-Heaven (Ailanthus altissima): Native to both northeast and central China, as well as Taiwan, the tree-of-heaven is an invasive, pervasive, and problematic tree. It is allelopathic, which means it produces a toxin that inhibits the growth of other plants. Controlling the tree-of-heaven is important because it can quickly crowd out native plants. It’s important to know how to recognize it, as there are several other trees that look very similar.
• Japanese barberry (Berberis thunbergii): This is an invasive non-native woody plant that can grow 3 to 6 feet tall and wide. It can very quickly dominate woods and woodland edges, crowding out native plants and disrupting ecosystems.
• Annual sowthistle (Sonchus olearaceus): Sowthistle reproduces from seeds and the seedlings form a basal rosette low to the ground. As they grow, they can reach approximately 4 feet tall.
• Mulberry weed (Fatoua villosa): A summer annual that can grow more than 2 feet tall. You can remove it by hand before the seeds set.
• Oriental bittersweet: This is a non-native woody perennial vine that covers and kills plants by blocking sunlight, weighing down plants, and girdling trunks and stems.
• Ragweeds: These are members of the Aster family. Common ragweed can be found throughout parts of the Northeast and has historically been a problem in soybean crops.
• English ivy (Hedera helix): This non-native woody perennial vine has been known to kill the trees of branches when left to grow unchecked. When allowed to grow up a structure it can be difficult to remove because of the root-like structures it uses to anchor itself.

Herbicides Application

You should take proper care when applying herbicides near trees and shrubs. Incorrect herbicide formulations can damage non-target plants. Glyphosate, a systematic, non-selective herbicide, is easy to use but very unforgiving. Overspray can be devastating to plants around it.

Before applying herbicides, take a close look at the label to see what active ingredients it contains. Manufacturers formulate some combination products in either amines or esters. You are required to obtain certification as a commercial or public applicator if you're planning to apply restricted-use pesticides. Spray record-keeping plays an important part in an integrated pest management plan.