We are losing some of our (40 year old) Douglas-fir trees to drought stress. Last year, about one acre on a 30 acre lot. These trees have very shallow roots and are in competition with increasing grass as the tree canopy dies back. I would like to reduce the competing vegetation and mulch around the trees. Is there a recommended herbicide I can use in the month of May around the bases of the 40 year old Douglas-firs? This timber was thinned in 2015, before that there was no grass. When the tree canopy fills in I would expect the competing vegetation to decrease. There are another four acres of shallow rooted trees adjacent to the dead trees. I know these are not great site conditions for Douglas-fir but would like to save them anyway. Most of the property drains better and the trees have much deeper roots.
Marion County Oregon