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Gusty wind may be spreading herbicides

KENNEWICK -- It certainly has been windy over the past several months.

The tattered and torn leaves on garden plants are obvious consequences of the worst winds.

However, the herbicide injury that's showing up here and there may be the result of windy or just plain breezy weather.

About a month ago, I was walking in a local park when I spotted herbicide injury on a large number of trees. The severely distorted leaves were characteristic of damage from phenoxy or growth regulator-type herbicides. This group of herbicides includes 2,4-D, MCPP and dicamba, common ingredients in many home lawn weed killer products.

The symptoms caused by these phenoxy herbicides varies some with the particular herbicide, the type of plant and the severity of the exposure. Generally, they cause distorted leaves and leaf petioles (leaf stems), cupping of leaves, twisted new growth and narrow straplike leaves. If damage is severe, tissues may first turn yellow, then brown and die. Some plants, including grapes and tomatoes, are very sensitive to damage from exposure to very low levels of the herbicides.

So how were the park trees exposed to the herbicide? One typical way would be an application of herbicide to the grass at a rate higher than recommended on the label. A look around at the large nearby patches of clover and other healthy weeds told me that wasn't how these trees became injured.

Another common means of exposure is through drift. This could have happened when someone, somewhere in the neighborhood applied an herbicide spray when the wind was blowing.

Herbicides applied as sprays never should be applied when there's any sort of breeze.

Drift and overapplication aren't the only ways gardeners unwittingly damage plants with herbicide. Herbicide injury to garden plants also can result from using contaminated mulches. If you collect the grass clipping when you mow the lawn, it's environmentally smart to compost them or use them as a mulch in the garden. However, the clippings should not be used if the lawn recently was treated with a broadleaf weed killer because they can contaminate the soil.

Whether applied to the lawn as a spray or in a granular form, the herbicide label will specify how long you must wait before you safely can use the clippings as a mulch or in the compost pile. If you use a lawn care service, ask them how long their product label says you should wait.

Not following the label directions is another reason herbicide injury occurs. A number of phenoxy herbicide products, especially those containing dicamba, advise against using them in the root zone of desirable plants. That's because the plants can take the chemicals up through the roots and result in injury. It's important to think about where the roots of plants are located, keeping in mind that the roots of trees and shrubs can extend a long way out from the base of the plant.

Labels on some products will warn against application when the temperature is above or expected to rise above 85 degrees soon after application. If it's hot out, these materials can vaporize and easily move off the target area and damage desirable plants. This can happen even with granular materials.

To stay out of trouble, never use any herbicide spray when its breezy or windy. Also, make sure you read and follow all the label directions on any weed killing product.

* Marianne C. Ophardt is a horticulturist for the Washington State University Benton County Extension Office.

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