Use tools, chemicals to manage weeds

By Marianne C. Ophardt, Special to the Tri-City HeraldSeptember 7, 2012 

PASCO, Wash. -- If you just have a few dandelions or other weeds in the yard, your best bet is to dig them out as soon as they're noticed.

This doesn't have to be back-breaking work. I just ordered a Fiskars Uproot Lawn and Garden Weeder that is supposed to make the job of pulling lawn weeds easy with no bending or kneeling. Just place the steel claws at the end of the long handle over the top of the weed, and step on a foot platform. It pops out the weed, roots and all.

There are similar tools available at local garden and hardware stores. Pulling may not be practical for extremely weedy or expansive lawns. Also, certain weeds, such as patches of clover or black medic, aren't easy to pull.

Chemicals are sometimes the only effective way to manage certain lawn weeds, but knowing what, when and how to use these materials successfully is important.

For broadleaf lawn weeds, such as dandelions, plantain, black medic and clover, the right time to apply a lawn weed killer (herbicide) is fall. Once the weather cools, September through October, is when these perennial weeds are sending food reserves to their roots. Most broadleaf weed herbicides available to homeowners contain a mix of 2,4-D, MCPP (mecoprop) and dicamba (Banvel). When applying a lawn herbicide, you may think the material hasn't worked because the weeds don't die quickly, but by springtime the weeds should disappear.

Fall is also a good time to apply broadleaf weed herbicides because you're less likely to damage garden plants through misapplication, drift or volatilization. Also, labels of mixes containing dicamba caution against using them in the root zone of trees and shrubs. Where nearby woody plants may be at risk, it's a good idea to spot treat the weeds in those areas.

Many perennial grassy weeds, such as Bermuda grass, in lawns can only be controlled by spot treating with a product containing glyphosate. Glyphosate is a nonselective herbicide that is taken up by green plant tissues and transported down to the roots. The chemical gradually kills the roots and the weed dies. Glyphosate is often the only effective material for managing dastardly tough perennial weeds in landscape beds, such as field bindweed.

The following are tips for using glyphosate:

* Apply to actively growing, healthy perennial weeds that aren't drought stressed.

* The more green leaf surface that's treated with glyphosate, the more chemical gets into the plant, and the more effective the treatment.

* Don't mow or pull weeds immediately before treatment and don't mow or pull for at least seven days after applying.

* When treating Bermuda grass, the most effective time of year is late summer when it's flowering.

* When treating field bindweed in landscapes, the most effective time of year is right after it begins to flower in early summer and then again when runners reach a foot in length.

* Avoid getting glyphosate on nearby plants by shielding them with a large piece of cardboard.

* Remember to follow Sun Tzu's advice and know when you can and can't fight weeds with chemicals.

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

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