How Safe is Triclopyr?

We have made the decision to again treat Lake Fairlee with the herbicide triclopyr (Renovate™).  Based on our experience with this chemical in 2010 and 2013 we believe this to be a safe and effective way to deal with the growth of Eurasian milfoil in our lake. At that time we did as much research as we could to reassure ourselves that what we were doing would not have any harmful effects.  You can see what we found then on the page called Herbicide Resources.

Can the chemical get into my well water?

Property owners who have wells near the lake, particularly shallow wells, have experssed concern for the safety of their drinking water supply.  The State of Washington’s Department of Health has looked at this question, and found:

“The limited mobility of triclopyr in soil, low absorption constant, and high rate of microbial and photolytic degradation in water and sediment would indicate that this compound would have little potential for the extensive mobility required to contaminate groundwater supplies.”

They go on to note that:

“This assumption is supported by data collected by the US Geological Survey (USGS), as this federal agency has collected over 850 groundwater samples over a five-year period in the Pacific Northwest area and these samples have been examined for pesticide residues. Triclopyr has never been detected in any of the groundwater samples taken by the USGS, despite extensive use as an herbicide in this region in forestry applications over a 20-year timeframe.”

We only know of one published instance of well water being tested for triclopyr after an adjacent lake was treated.  In this case the level detected was 0.0 ppb after two weeks.

 How do we know it is safe?

Triclopyr is a manmade chemical that does not occur naturally.  Although it has been used for more than three decades without any recorded incidents, how can we know that it never will?  It is hard to prove a negative.

Knowledge is power, and in this case we believe that understanding more about what triclopyr is and how it works can inform our belief in its safety for this use.

Auxins are a class of plant growth hormones.  They are involved in the regulation of the growth of plant cells.  They are directly responsible for phototropism, the tendency for a plant to grow towards the sun.  A simplified version of the way this works is that within a given cell the auxins are inhibited by sunlight, so the growth occurs more at the end of each cell that is not exposed to sunlight, and the whole plant appears to reach towards the sunlight.

A little about auxins

Chemical formula for triclopyr

Triclopyr is a synthetic chemical called an auxin. Auxins are a class of chemicals found in plants that help regulate their growth. For example, phototropism is caused by inhibition of auxins by sunlight, so that the shaded underside of the plant grows more than the sunny part, causing the plant to ‘grow toward the sun.’  Abnormal amounts of these auxins can disrupt the normal growth of a plant, even kill it, so auxins are also used as herbicides.  Also, different species of plants respond differently to auxins, making them useful for weed control. Finally, triclopyr is an effective herbicide for dicots(flowering plants and trees) but not for monocots (grasses and conifers).  More information HERE.