Beware Herbicide Damage to Trees

6/26/2013

MANHATTAN, Kans. - Megan Kennelly, a plant pathologist at Kansas State University, located here, writes in the latest KSU Turfgrass Blog that on recent walks she is seeing what she suspects is herbicide damage to trees. She warns that herbicides can injure trees.

Along with several photographs showing symptoms of what appears to be herbicide damage, she posted a brief writeup from colleague Ward Upham, home horticulture Rapid Response Coordinator for extension agents across Kansas. 

Here is Upham's helpful and timely article on the subject:

This seems to be a year in which we are seeing a great deal of damage caused by exposure to herbicides. Symptoms vary with herbicide applied, plants exposed, concentration of product and environmental factors. Here is a list of the types of damage commonly seen.

Broadleaf herbicide drift. A number of herbicides used on farms and on home lawns are essentially plant growth hormones. These include 2,4-D, triclopyr, and dicamba and are commonly used to control broadleaf weeds in lawns, pastures, or grassy crops. These products may volatilize (become a gas) at high temperatures and may drift and damage non-target plants such as trees and shrubs.

Symptoms may include twisting and distortion of plant foliage, leaf yellowing, and, in severe cases, branch dieback. One of the trademark signs of this damage is the curly-Q twisting of leaf petioles or stems. Though some species of woody plants such as redbud and grape are very sensitive to these herbicides, usually a number of species will show some damage if drift has occurred. If you see twisting on more than one woody species, chances are that herbicide drift has occurred. Often plants will recover from drift due to volatilization.

Damage from stump or sprout treatments. Tree stumps are often treated to prevent resprouting. Two commonly used products are picloram (Tordon) and triclopyr (Remedy, Stump Killer, Brush-B-Gon, etc.). Be careful when applying these herbicides to prevent contamination of the soil. Nearby trees may be damaged if they pick up enough herbicide. Foresters warn that picloram may also leach from roots of a treated tree into the soil and then be absorbed by roots of another tree species.

Be very careful about using these products near valuable trees and shrubs.

Sprouts are often treated to keep them from growing where they interfere with the aesthetics of a lawn or other landscaped area. Never use a herbicide to treat sprouts coming from a root system of a tree you want to keep. A number of tree species including honey locust, black locust, hackberry, western soapberry, persimmon, and occasionally maples may send up sprouts from their roots. Treating these sprouts will effectively treat the tree to which they are attached. This may ultimately kill the tree. Also remember that trees of the same species growing next to one another may share a root system as a result of root grafting. Treating one tree in the group is like treating all of the trees.

Liquid Weed Edgers. Herbicides are often used along fences, on sidewalks or gravel drives to prevent plant growth. Some of these, including glyphosate (Roundup) and glufosinate (Finale) rarely cause damage unless sprayed directly on the foliage of a shrub or tree. Other liquid weed edger products are soil sterilants and have a long residual (months to years) in soil and are highly toxic to trees and shrubs. Symptoms may include yellowing, marginal leaf scorching, branch dieback and tree mortality. Once the tree takes up these products through their roots, they suffer permanent damage.

Never use these soil sterilants in areas where tree roots may be exposed. Remember that tree roots extend well beyond the so-called drip line. It is almost impossible to use liquid weed edgers in the landscape without coming in contact with tree roots. Also remember that some of these products, such as prometon, will move with water until they become affixed to the soil.

Those of you providing services in and around Kansas might want to check out the KSU Horticulture Newsletter by clicking here.

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