Landscape - Herbicide Damage to Trees

Two common herbicides, 2,4-D and dicamba are used extensively for control of broadleaf weeds in turf and are commonly included in broadleaf herbicide formulations. Unfortunately, they can also damage nearby trees and shrubs if not used correctly. The following is information on these two herbicides and the damage they can cause.

2,4-D is one of the most common herbicides used in the home landscape and is often associated with plant injury. The most common symptoms are a twisting of the petiole which results in the leaf turning upside down. There are sucking insects whose feeding activity will also result in a leaf to curl or twist but their feeding will not cause the petiole to twist. The lowest residue that will produce symptoms in susceptible tree species is 0.02 ppm. The species that are the most sensitive to 2,4-D injury include boxelder, birch, hackberry, green ash, honeylocust, walnut, poplar, littleleaf linden and elm.

Dicamba is another frequent herbicide associated with plant injury. Dicamba will produce similar symptoms to 2,4-D at low concentrations but in addition to the leaf curling or twisting there is often a proliferation of short shoots. Oftentimes there will be a swelling of the shoot. Dicamba injury frequently occurs from root uptake as applicators ignore the precaution that this herbicide should not be applied within the dripline of trees. The dripline is considered to be the edge of the tree’s canopy, the furthest extent of the roots, but the root system can extend out a distance equal to the tree’s height. Since the concern about applications within this zone is possible uptake by the roots it is best to restrict applications to a distance further than the height of the tree. The lowest residue that will produce symptoms in susceptible tree species is 0.03 ppm. Tree species that are most sensitive to dicamba include: boxelder, birch, catalpa, honeylocust, apple (and crabapple), spruce, poplar, oaks, littleleaf linden and lilacs.

Reprinted in part from the January 2008 Pest Update from South Dakota State University