Roundup also offers products containing the nonselective herbicide glyphosate. These products will kill thistles but will also kill your lawn and other desired plants. ... Keep children and pets off the lawn until the herbicide dries.

What is the best herbicide to kill thistles?

Apply herbicides to kill thistle, especially in spring and fall, before thistles can flower and seed. Use glyphosate for your garden, and use a broad-leaf herbicide containing 2,4-D or MCPP for your lawn. Since glyphosate kills all plants, you must keep application specific.

What will kill thistles?

Among myriad available weed sprays, glyphosate proves to be effective on thistle. Apply to individual cut stems an inch or two above the soil line, taking careful aim of the weed sprayer to avoid contact with desirable plants. Reapplication in several weeks may be needed for well-established thistle.