Herbicide drift and your garden
A recent news report on National Public Radio described problems organic gardeners are having with pesticide drift from their neighbors. Pesticide drift is an issue not limited to organic gardener, but is a problem for conventional gardeners and farmers as well.
Pesticides include all materials, organic and synthetic, used to manage, control or eliminate a pest. When you spray 2, 4-D or glyphosate to kill weeds, an insecticide to kill insects, a miticide to manage mites or apply iron phosphate around your hosta to control snails and slugs, you are applying a pesticide. The pesticides that cause the most problems are herbicides. Whether applied by you as a homeowner or a commercial applicator, drift of the spray droplets can occur. To make things worse, herbicide sprays can vaporize and the vapors drift off target causing damage. Every year, trees, shrubs, vegetables and flowers in western Colorado die, or are severely damaged, from pesticide drift.
Some of those cases are due to a neighbor applying the wrong pesticide or in a manner that increases the possibility of drift. In other cases, a commercial applicator was not paying attention to the application. The size of the spray particle, wind speed and temperature are often cited as causing the most drift. Coarse droplets fall to the ground faster, and are less likely to drift, than small droplets. Opening the nozzle orifice to increase droplet size and using low-pressure results in larger droplets and less drift. The smaller the droplet, the longer it remains suspended and the further it can move in the air currents. The height of the nozzle above the target also impacts drift. The higher you hold the nozzle above the target, the more likely drift will occur.
Using an ester formulation of a pesticide increases the chance of vapor drift. Even non-ester formulations of pesticides can vaporize when sprayed on a hot surface on a hot sunny day. When the air is dead calm, vaporization increases making this one of the worse times to spray, especially on a hot day. The smaller droplets suspended in the air evaporate and drift long after the application is made. Another time spraying should be avoided is when the wind is gusty. The ideal time to spray is when the wind speed is between two and six miles per hour. At this speed the leaves rustle, twigs will be in motion, and you feel the wind on your face. Higher wind speeds pose a greater chance for drift.
If the pesticide drifts off target and damages someone else’s plants, the applicator is responsible for the damage. Homeowners often get in touch with me when they notice curling and distorted leaves and want to know the cause. Sometimes the damage is caused by the herbicide they applied. If I determine the damage is caused by an application made by a commercial applicator, I provide the homeowner information on how to file a complaint. If they proceed with the complaint I forward a copy of my report with photos to the Colorado Department of Agriculture. The CDA follows up with an inspection, sampling and civil or legal action if needed. If the herbicide is due to an application made by a neighbor, civil action may be the only option available.
If you suspect herbicide damage give me a call at 970-778-7866 for a consultation.
Free Press columnist Dr. Curtis E. Swift is a retired horticulture agent with the Colorado State University Extension. Reach him at Curtis.Swift@alumni.colostate.edu, 970-778-7866 or check out his blog at http://SwiftsGardeningBlog.blogspot.com. He owns Swift Horticultural Consulting and High Altitude Lavender.
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