Have you identified your "weeds" and invasives?

Denise,

If all your spring ephemerals have died back, if there's NO hint of them above the ground at all....then go ahead and use round-up. April

Fall is a good time to hit poison ivy, shrub lonicera and multiflora rose with RU. I am not sure whether it would work well on garlic mustard seedlings, but it's worth a try on a test patch.

Be sure to just use the regular strength roundup which is safer even though you might have to spray two or three times for stubborn weeds like honeysuckle and poison ivy.

This spring, I sprayed a small area of low-growing winter weeds in the woodland garden (speedwell, geraniums, chickweed, wintercress, etc.) with Roundup Brush Killer and poisoned the ground - stunting or killing most of the spring emphemerals that were still underground.

have you considered doing a prescribed/controlled burn?