Herbicide Damage to Trees, Shrubs and Gardens Every year we see 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 become a gas
(volatilize) at high temperatures, causing them to drift and damage
nontarget 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 tomatoes, redbud trees, and grapes are
sensitive to these herbicides, a number of species will show some damage if
drift has occurred. If you see twisting on more than one species, chances
are that herbicide drift has occurred. Often, plants recover from drift due
Damage to vegetable gardens. Though drift is the most common cause of
herbicide damage on vegetables, other potential problems exist as well.
Cattle fed prairie hay from pasture treated with picloram (Tordon) can have
manure tainted with the herbicide. If this manure is used on a vegetable
garden, plants may sicken and die. Also, lawn clippings treated with
quinclorac (a crabgrass killer) and used as mulch can have the same effect.
Both products can remain active for up to 24 months.
Damage from stump or sprout treatments. Tree stumps often are 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 also may leach from roots of a treated tree into the soil and be
absorbed by roots of another tree species. This does not occur with
triclopyr. Be very careful about using these products near valuable trees
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
If treating volunteer sprouts, use a product such as Monterey
Sucker-Stopper. It will not harm the plant to which the sprouts are
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 causes 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 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.
By: Ward Upham