By Curtis Utley, Jefferson County Extension
With the fantastic moisture we have received along the Front Range this spring homeowners are seeing weed growth exploding and with cool temperatures many, myself included, have not been puttsing around in the yard pulling the wayward weeds as frequently as in years past. If you are considering tackling your over-gown weeds with chemical herbicides be aware of a few possible pitfalls and read the entire label before purchasing an herbicide and making an application. Label information is provided to consumers to protect you, your yard and the environment. There are selective herbicides that will kill broadleaf weeds growing in your lawn without killing your grass. There are also selective herbicides that can kill the grass growing in your flower or perennial beds without killing your flowers. There are also non-selective herbicides that will kill anything green, and lastly, preemergent herbicides prevent seedling establishment.
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| Phenoxy herbicide damage to a perennial bed due to over-spray |
The most commonly available weed killers sold to consumers are the phenoxy herbicides. Common phenoxy herbicides include: 2,4-D, Dicamba, mecoprop-p (MCPP), and MCPA. Phenoxy herbicides are selective herbicides that kill broad-leafed dicotyledonous plants and do not harm grasses and other monocots. Phenoxy herbicides are auxin mimics and cause hormonal changes leading to rapid uncontrolled growth leading to the death of susceptible plants. The herbicide targets the growing points where cell division is rapid. The symptoms of phenoxy herbicide damage include, twisting, curling and rolling of leaf and stem tissues. A few weed control products containing the auxin mimics are sold as hose-end products or are permitted to be applied in an aftermarket hose-end sprayer. While this application method is simple and fast I strongly caution against applying herbicides through such a device due to the potential for overspray. Hose-end sprayers can produce variable droplet sizes which can allow for particle drift resulting in unintended consequences. The other potential issue with hose-end sprayer applications is 2,4-D volatilization. If you apply a broadcast application of 2,4-D on a day when temperatures climb above 85 degrees F. the herbicide can become a gas and float on air currents damaging trees and shrubs.
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| Phenoxy herbicide injury to green ash due to 2,4-D volatilization |
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| Phenoxy herbicide injury to red oak due to 2,4-D volatilization |
Herbicide applications are best accomplished by spot spraying individual weeds with a pump up sprayer. You will use less product, saving money, and can safely direct the application to weed leaves. Spot spraying and adjusting your spray nozzle to produce a course spray pattern greatly reduces the risk of over-spray, herbicide drift and volatilization.
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| Dandelion dying after a spot spray application of 2,4-D |