Answer: Some weeds are terribly persistent and even weed killers will only kill the parts of the plant they come in contact with. Perhaps there's a special technique with the weed you're dealing with. Why not dig one up and take it to your local cooperative extension office or Master Gardener clinic for positive identification? Helpful folks there can offer control strategies. Contact WSU Spokane County Extension, 222 N Havana, Spokane WA 99202-4799, 509-477-2048.
Best wishes with your landscape.
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