This is the time of year that weeds get our attention. As soon as warm weather hits, they seem to be everywhere. Then out come herbicides (weed control chemicals) aimed at killing these unwanted pesky plants in our lawns, landscapes and gardens. Unfortunately, not using these chemicals properly can injure or kill desirable plants.
Symptoms of herbicide injury vary depending on the chemical, but common culprits are the growth regulator-type herbicides used to kill broadleaf weeds, such as dandelions, in lawns. Exposure can cause leaf cupping, twisted or distorted growth, and strap-like leaves. The common growth regulator herbicides found in home garden products for lawns are 2, 4-D, MCPA, MCPP and dicamba.
These products are available in liquid or dry form. However, because of the wind, it is easy for spray to drift away from the target area. Therefore, these sprays should only be applied when there is no wind.
In our region, where it is frequently windy, this is difficult. The potential for drift can also be reduced by using large spray droplets instead of a fine mist, and applying the spray as close to the ground as possible.
The other application choice is a dry form, but desirable plants can still be damaged because of uptake of chemicals through the roots. The labels of products containing dicamba indicate that it should not be used “in the root zone of desirable plants.”
If you have trees in or adjacent to your lawn, it is almost impossible to avoid applying the chemical in the root zone. Tree root systems can extend as far as a tree is tall and even further. Garden plants situated next to a treated area could also become damaged via root uptake.
Plants can also be exposed to herbicides when grass clippings from recently treated lawns are used as mulch in the garden. Check product labels for how long you must wait before using the clippings. If you place treated clippings in a compost pile, it is best to compost them for several months before using it in the garden.
Other ways to reduce the chance of herbicide injury in the yard and garden include:
w Avoid applying herbicides in late spring and summer. They can vaporize during warm (above 80 degrees) weather and float in the air, settling down on plants a long way from the point of application and causing damage. If you plan to use liquid or dry herbicides, do it when the weather is cool in early spring or fall.
— If you have a few weeds in the lawn, spot treat them individually or dig them out. A weed popper tool works great for this.
— In landscape beds, apply a 3- to 4-inch layer of bark mulch to discourage weeds.
— In and around the vegetable and flower garden beds, use shallow cultivation or pull the weeds. I like a stirrup-type hoe with an oscillating head. Cultivate frequently to get the weeds when they are small. It is much easier.
— Marianne C. Ophardt is a horticulturist for Washington State University Benton County Extension.
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