Bent outside collars

Some of the collars have some bentgrass outside the collars. I plan on spraying it out but have to wait until the Bermuda goes completely dormant. Once that happens we will spray out this bentgrass with roundup (roundup doesn't affect dormant Bermuda). There are chemicals that will kill the bent without hurting the bermuda but this type of herbicide has a tendency to move with water in the soil. This is dangerous to spray around greens because one heavy rain could move it into the greens, killing the grass on the greens.