What's the best way to control weeds near trees? I live on a half acre lot that has a couple older trees and several young trees that I am trying to grow. My lawn is overrun with weeds, mostly annuals but there are also a couple hundred dandelions. Last year I let my father-in-law treat the yard, we used Bonus S (atrazine) and also a three-way Weed-B-Gone a couple weeks apart. This took care of weeds for the year but also killed off 3 trees I had planted and damaged the older trees (lots of curling leaves). We were careful not to get anything on the trees so it must have been picked up by the roots.

I've considered spot treating the dandelions this year, putting down a pre-emergent this fall, and hoping that will take care of most of it. Are pre-emergents safe to use around newly transplanted trees? I'm planning to plant 2 or 3 more this fall. Every pre-em label I have read says it can only be used near "established" trees but does not define how established it must be. Is there any other advice anyone can offer?