Garden Tips: Avoid herbicide injury to plants

For the Tri-City HeraldMay 23, 2013 

When weeds appear in the lawn and landscape, many homeowners turn to chemical weedkillers to take care of the problem. Herbicides (weedkillers) kill plants. That is what they are supposed to do. When used correctly, they can be an effective tool. When used improperly, they can damage desirable plants.

Before you reach for a weedkiller, here are some guidelines for using these chemical tools:

1. Read the label — the entire label — before using the product. Many of the “weed and feed” products or broadleaf weedkillers contain a combination of 2,4-D, MCPP and dicamba. Somewhere on the label of these products it will note that they should not be used in the root zone of “desirable trees and shrubs.” If you have a landscape with established shade trees, you will be applying these materials in the root zone of “desirable trees and shrubs.”

So what can you do if you have weeds and trees in your lawn? If you just have a few weeds here and there, don’t use an herbicide product over the entire lawn. Spot spray the individual weeds or dig them out. I like the “weed popper” tools like Fiskars Uproot Lawn and Garden Weeder or Grampa’s Weeder (grampasgardenware.com) that use leverage to pop out the weeds along with most of their roots. This avoids tedious back-breaking digging with a hand weeder.

2. If you’re not using a ready-to-use product in a spray bottle, it’s wise to use a separate garden sprayer for herbicide sprays. If a sprayer is not cleaned thoroughly, you can end up damaging your plants with a contaminated sprayer.

To clean a sprayer:

-- If you can’t use all the material you have mixed, spray it somewhere in the landscape where it won’t harm plants. Check the label to determine what areas are safe. Do not store any mixed product in your sprayer.

-- Check the product label for specific directions on how to clean the sprayer after using the product. If there are none, thoroughly rinse the tank, hoses, wand, nozzle and any other parts with water. Spray the rinse water over a wide area that will not cause damage. Don’t dump it on the ground or down the drain.

-- After cleaning the sprayer when using 2,4-D or a similar herbicide, fill the tank with water and add ammonia (1/3 cup of ammonia per gallon of water). Allow it to soak for 24 hours, being sure that the ammonia solution is also run through the sprayer and all its parts before soaking. This will remove much, but not all, of the 2,4-D from the sprayer.

3. Damage to plants from weed killers can also be caused by drift that occurs when sprays are applied when it’s windy. It is hard to find a calm day in this region, but you should never apply herbicides when the wind speed is more than 15 mph. It’s best to wait until the wind is 5 mph or less. Also, the larger the droplet size, the less likely the material will drift off target.

-- Marianne C. Ophardt is a horticulturist for Washington State University Benton County Extension.

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