Late summer and fall is a good time to work on tough-to-control perennial weeds such as Virginia creeper vine, grapevine, milkweed, goldenrod, poison ivy and brambles. These perennials generally do not respond to soil applied herbicides, but can be managed by careful applications of glyphosate (Roundup) in the fall. Glyphosate is effective on these weeds, but will also kill berry plants. Perennial weeds succumb because the plant is moving carbohydrate reserves down into the root system at this time of year. So treated leaves quickly move the systemic herbicide glyphosate down into the crown and root. You need to treat before the leaves drop though - so the clock is ticking. Some woody weeds like Virginia creeper vine, drops its leaves early in the fall.