Should Roundup Be Sprayed Near Shrub & Tree Roots?

How It Works

• Roundup's active ingredient, glyphosate, is a nonselective herbicide. This means it can kill any plant that absorbs enough of the chemical. Smaller plants absorb the herbicide through leaves and stems, but most tree and shrub bark is thick enough to block the chemical; it usually enters the tree or shrub through the leaves or open wounds on the trunk and branches.

Roundup in the Soil

• According to Monsanto, Roundup bonds with soil particles and doesn't travel through the soil to tree and shrub roots. The herbicide won't leach into the soil, soaking down when watered to absorb into root systems. Instead, it breaks down quickly in the soil; you can plant new trees -- with fresh, exposed roots -- in the glyphosate-treated soil as soon as seven days after application.

Herbicide Drift

• A bigger danger than soil leaching is herbicide drift. This occurs when you spray weeds near a tree or shrub, and the wind carries drops of the herbicide to leaves of those plants. A few drops are unlikely to kill a tree or shrub, but when a large portion of a fine spray mist travels to the leaves, it could potentially cause severe damage or death to the plant. Roundup is most dangerous in the summer and fall, when sap is transporting nutrients from the leaves to the roots. In spring, many trees have sap moving upward to feed the branches and leaves; Roundup isn't quite as effective on trees and shrubs during this time.

Signs of Damage

• Within 24 hours of applying Roundup, check nearby trees and shrubs for signs of herbicide drift damage. Leaves might develop brown spots or curl at the edges, and some might be completely brown and fall off the tree or shrub. Pluck affected leaves as soon as you notice damage, although this won't necessarily stop the progression of the herbicide when it's headed for the roots. Instead, it helps the tree focus energy on keeping remaining leaves healthy. A few damaged leaves doesn't signify a problem. However, if you see a large section of the tree or shrub with dead or dying leaves after spraying herbicide nearby, the plant might be irreparably damaged and could die.