Will Roundup Kill Trees?

Active Chemical

• Glyphosate is a broad-spectrum, systemic herbicide sold under different trade names such as Roundup. The nonselective herbicide kills nearly all perennial and annual plants, including woody plants such as shrubs and trees. Glyphosate is classified as a general-use herbicide and is also widely used to control sedges, grasses and wide range of broad-leaved weeds.

Use Method

• Apply the chemical as a foliar application to trees that are up to 15 feet tall. On larger trees, cut the tree to a stump, and treat the stump with the chemical. If the trunk diameter is 3 inches or less, spray the entire stump surface. On trees with a trunk diameter of more than 3 inches, spray only the 2 to 3 inches next to the bark, as the inner heartwood is naturally dead. Apply herbicide to the fresh-cut stump immediately.

Use Suggestions

• When applying Roundup as a foliar spray, make sure the tree is evenly coated from all sides. Do not spray to the point of runoff. Avoid using the chemical on very hot days and on drought-stressed trees, as this reduces efficacy. The herbicide is most effective when applied to fresh-cut tissue on a stump. If treatment is delayed after cutting trees, recut the surface to expose fresh tissue before applying Roundup.

Application Time

• Glyphosate is most effective when used during August and September, according to the Washington State University Extension. Actively growing trees with mature and fully developed foliage respond best to treatment. Roundup is a nonselective herbicide and will adversely affect all plants or grass that it contacts. Use it carefully, and avoid use on windy days to minimize drift to desired plants. Avoid using Roundup if rainfall is expected within six hours of application, as the moisture will reduce its efficacy.