Don't pull weed

Garden Q&A

use herbicide

Garden Q&A

September 09, 2006|By Jon Traunfeld and Ellen Nibali | Jon Traunfeld and Ellen Nibali,Special to The Sun

I have a weed with thorns on the stems and leaves and now a small purple flower. It's killing my phlox and invading the lawn. I pull it, but the roots are never ending.

The weed in your photo is Canadian thistle, an invasive Eurasian perennial with a deep, extensive root system. Don't hand-pull this weed because any piece of missed root will sprout into additional plants. (You can very carefully dig up tiny seedlings before roots are established.)

In your ornamental bed, spray an herbicide that contains glyphosate on foliage or freshly cut stems. It will travel through the plant to the roots. Glyphosate is a nonselective herbicide, so be sure desirable plants are shielded. You may need to spray twice.

In lawns, treat thistle with a selective broadleaf herbicide containing a combination of 2,4-D, MCPP and dicamba, often known as Trimec. Follow directions precisely because dicamba can go through the soil and damage nearby trees' and shrubs' roots when used incorrectly.

Never allow thistle to produce seeds, which float off to invade parks and natural areas where thistle out-competes essential native plants.

Jon Traunfeld, regional specialist, and Ellen Nibali, horticulture consultant, work at Maryland Cooperative Extension's Home and Garden Information Center, which offers Maryland residents free gardening information. Call the center's "hotline" at 800-342-2507 (Monday through Friday, 8 a.m.-1 p.m.) or e-mail plant and pest questions through the Send a Question feature at hgic.umd.edu.

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