JoAnne Skelly: Be careful when using herbicides

This warm winter weather makes weeds grow. A few weeks ago, I saw filaree blooming. Cheatgrass is growing, even with the drought. As these and other winter annual weeds grow and before the spring weeds get started, people are thinking of spraying. They want to kill weeds that have started and prevent any new weeds from germinating in the first place.

The goal in spraying herbicides is to control weeds. Seems obvious, right? However, people often accidentally apply chemicals to desirable plants or soil through spray drift and volatility.

Drift, having the wind blow the herbicide onto plants you want to keep or areas you hope to seed, is a common problem. Small drops of chemical in the wrong place can damage and even kill desirable plants or prevent seeds from growing. Drift can land in waterways causing environmental damage. It if lands on your neighbors’ plants, it may cause economic damage for which you are responsible.

Volatility is when a chemical converts to a gas and moves from the site of application. Sprayed herbicides can change to a gas with an increase in temperature. This occurs most easily when the herbicide missed plants and landed instead on hard surfaces, rock or pavement. Wind then moves the gas into a non-target area, either near or above the targeted site, damaging or killing plants.

I have known people to spray their lawn for dandelions on a warm day and then call me a few days later to ask why their trees looked so bad. The gas volatilized off the sprayed weeds in the lawn and up into the trees where it was absorbed by leaves into the tree.

The best way to minimize damage due to drift is to avoid spraying when it is windy or if wind is expected before the herbicide can dry. Spray carefully if there are desirable plants near or downwind. Keep the spray nozzle low and move it slowly rather than waving it around. Always read and follow the label and properly use the designated equipment mentioned on the label.

To reduce volatility, avoid applying herbicides in high temperatures and low humidity. Avoid spraying on impermeable surfaces including rocks and pavement. Use formulations that are readily absorbed by plants. Read and follow the label carefully.

When you use an herbicide, you are a pesticide applicator and are responsible for applying it according to the label. The label is the law.

JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension and may be reached at or 887-2252.


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