JoAnne Skelly: Soil sterilant herbicides – are they worth the risk?

Every gardener’s dream is to never weed again. When people read that an herbicide kills all unwanted plants, they think they have found a miracle cure for their weed problems. It is important to understand how these soil sterilant products work and what problems can result from their use.

Soil sterilant herbicides are “total kill” non-selective products that last in the soil for long periods, sometimes for 10 years or more, particularly in arid environments. They have the potential to unintentionally cause significant damage to desirable plants because roots, particularly tree roots can extend long distances from a tree.

Soil sterilants are meant for use in non-vegetated areas, such as industrial sites, parking lots and roadways, or where undesirable plants could cause damage, present fire hazards, or impede work crews. They are not designed for home use around gardens and landscapes.

In addition to lasting in soil for years, most soil sterilants are very water-soluble. They can move downward or laterally through soil with rain or irrigation water to the roots of desirable plants, especially when applied on a slope. The result can be death or serious injury to desirable plants even though they are located a distance from the original application site. Even rinsing a sprayer or washing off equipment near desirable plants can damage or kill those plants.

Because these chemicals remain in the soil for so many years, they can continue to spread with water movement year after year. Runoff can contaminate surface and ground water supplies. Label directions usually prohibit using these products near drinking water reservoirs or where wells may be recharged.

Long-term use of soil sterilants will cause bare ground that is prone to erosion. The only plants that might grow on these sites are often noxious weeds. Weeds also may develop a resistance to the product, becoming more difficult to control.

Before you use any pesticide, you must read the entire label. Labels include information about sites in which products can be used, special warnings or restrictions relating to environmental hazards, and the types of plants that can be controlled by the product. It is a violation of law to apply a product in an area that is not specified on the label.

“If it sounds too good to be true, it probably is,” applies to soil sterilant herbicides. Replacing trees and paying for offsite damage to neighbors’ plants can be costly to rectify. It is difficult and expensive to clean up contaminated drinking water, rivers, streams, or lakes. The risks of using soil sterilants far outweigh the benefits to homeowners.

JoAnne Skelly is Associate Professor & Extension Educator Emerita at University of Nevada Cooperative Extension. Email skellyj@unr.edu.