Answer: To control the briars, keep cutting the stems down and as soon as you have made a cut, carefully spray or paint on a weed killer such as Round Up or Brush B Gon. Either of these products will harm your roses if sprayed onto the plants or if the product is spilled onto the soil where it can be taken up by the roots of your roses so extreme caution is required. But if you cut and carefully paint the stubs of the brambles, they will eventually die out. Just be persistent. Between the weed killer and the physical act of cutting the stems off, the roots of the brambles will eventually die out.
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