Article contributed by Eddie Ayers, Fannin County Extension Coordinator, 205 Church Street, Suite 1, Blue Ridge.
Proper Use of Herbicides

A fellow County Extension Agent, Paul Pugliese, and I were talking the other day about using herbicides in the yard and how a herbicide designed to kill weeds in turf grass can also kill neighboring trees and shrubs so todays article is about the proper use of herbicides.

Herbicides in the phenoxy chemical class provide broadleaf weed control in lawns, pastures and hay forages. Some of the more common chemicals in this class include 2,4-D; MCPP; dicamba; clopyralid; and triclopyr and they’re considered very safe, leaving very few toxicity concerns for pasture animals. In fact, many of these herbicides are labeled for pasture use and allow for livestock to continue grazing without any restrictions, however, pesticide labels should always be read and followed to determine if any special precautions should be taken for specific site uses.

Phenoxy herbicides actually provide selective weed control, which means they control many broadleaf weeds without causing damage to grass. Of course, each product is a little different and some are labeled for very specific turf grass types, depending on their tolerance, so be sure to check the label before applying to a certain lawn type such as tall fescue, Bermuda grass, Zoysia grass, etc. and if turf grass isn’t on the label, don’t assume the herbicide can be applied to all lawns.

Unfortunately, phenoxy herbicides don’t discriminate between dandelion weeds or any other broadleaf plants, including many trees and shrubs, so it’s very important to take extra precautions when applying these herbicides near landscaped areas with ornamental plants. You should also consider the potential for drift damage to nearby plants and avoid spraying herbicides on a windy day.

There is also the potential for movement of herbicides through runoff and leaching in the soil. This is why the product label usually warns against spraying within the root zone of trees and shrubs and never exceeding the maximum application rates listed on the label. The biggest misconception concerns where the root zone of a tree or shrub exists. The roots of mature trees and shrubs actually extend well beyond the drip line of the canopy. Research shows that absorption roots may extend as much as two to three times the canopy width. Consider spot-spraying to target individual weeds rather than broadcasting applications across the entire lawn and never exceed the labeled rate.

The high potential for herbicide damage to trees is another great reason to protect tree roots by providing a mulch zone that extends well beyond the drip line of the canopy. If you’re not trying to grow a manicured lawn underneath a tree, then there is no reason to apply phenoxy herbicides there for weed control.

One more way to avoid potential damage is to rely less on phenoxy herbicides. Other classes of herbicides have less potential to affect the roots of nearby trees and shrubs, so take the time to identify your weeds and choose a more selective herbicide rather than combination products that usually contain multiple chemicals in the phenoxy class.

Many pre-emergent herbicides can prevent weed problems in lawns. The key is to apply them at the correct time in the spring and fall. Applying too early or too late often provides inadequate weed control and requires additional herbicide applications. Also, rotating pre-emergent herbicide classes will avoid the potential for resistant weeds but be sure to apply water to the area according to the pre-emergent herbicide’s label to activate it in the soil.

For more information, contact me at the Gilmer UGA Extension office at 706 635-4426.