Active ingredients are listed on the front of pesticide containers (yellow arrow above). The complete label, including instructions, may be on the front or back of the bottle and will require opening to read (blue arrow above). / Photo Credit: Wisconsin DNR

By Linda Williams, DNR Forest Health Specialist
Linda.Williams@wisconsin.gov or 920-360-0665

This is your reminder to always read pesticide labels, even if you think the product you are using is the same product you’ve always used.

Do you always check the active ingredients listed on the front of pesticide containers – and read instructions on the use of the product – every time you buy a new container of pesticide? It has become more important than ever to do so.

Glyphosate was previously the active ingredient in most RoundUp products and was also commonly used in generic brands used by homeowners to kill plants. That has changed. Now, products marketed for home, yard and garden use have different active ingredients that may not act the same as you remember glyphosate acting.

There are many products on the market that kill weeds or kill all plants. Sometimes, a single product can contain two or three active ingredients. So, it’s important to know what their active ingredients are, how they work, whether they bind to soil or move through soil, how long they remain active in the soil, and whether they will easily volatilize and move in the air.

Recently, a landowner had concerns that many of his large trees were dying. Examining those trees, it was clear that herbicide damage was the issue. The landowner said that they had used the product GroundClear to spray their driveway and trails, as they “have done for years.”

The issue was that they had previously used glyphosate products, and this year they used GroundClear Year Long Vegetation Killer with the active ingredient imazapyr. (Note that other formulations of GroundClear have different active ingredients and may not contain imazapyr. Check the label.)

Unlike glyphosate, imazapyr can move in the soil. The landowner was experiencing this, as runoff from his trails flowed into the rooting zone of trees along those trails. Even trees that were more than 50 feet from the trail were being affected.

Additionally, imazapyr remains active in the soil for a year or longer, and over time, it may continue to move downslope even further from the sprayed trails.

The GroundClear label clearly lists multiple restrictions, including:

• DO NOT use … over the root zone of trees and shrubs.
• DO NOT apply to slopes as movement on the soil surface may damage desirable plants down the slope.
• For shrubs and trees, DO NOT apply closer than twice the distance from the trunk to the drip line, as roots may be within this area.

The bottom line is clear: Always read the label.