Answer: Very often there is regrowth from poison ivy and other brushy weeds after initial spraying. Poison ivy can sometimes require multiple treatments. These can be spot treated with herbicide containing glyphosate. Read and follow all of the label directions. This is a nonselective herbicide and will kill your desired plants as well as weeds or brush. You may find that a wipe-on application method gives you better control over the herbicide.
You may also be seeing maple seeds germinating. These can be pulled easily when they are still very small.
In an area shaded by trees, it is best to plant a shade tolerant groundcover. Some to consider might include Pachysandra, Vinca minor, Epidmedium or hostas and ferns for example. Lawn grass generally will not grow well unless there is at least a half day of full direct sun and little competition from tree roots.
If your maple trees have extensive surface roots it may be very difficult to establish a new planting. The reason is that the deep shade combines with the moisture-stealing surface roots to make difficult growing conditions. (Surface roots should not be covered with soil.) If this is the case, you may want to consider using an organic mulch layer to cover the ground and perhaps create a seating area in the cooling shade of the tree.
I hope this gives you some ideas.
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