Using broad leaf weed killer in the root zone of a large tree

Asked July 12, 2017, 12:58 PM EDT

I have a lawn full of Common Lespedeza under my huge Willow Oak tree. I want to kill the Lespedeza without harming the roots of the Oak. Most all the Broad Leaf Weed Killers contain Dicamba which I have been told will damage the roots of trees. What can I use to kill the Lespedeza that is safe for the roots of my Oak Tree, and will not kill my grass ? Thanks for your help.

Montgomery County Maryland

1 Response

We do not recommend using dicamba in this setting. Consider covering with landscape fabric and a light layer of mulch. Herbicides in general are not recommended under this tree. Covering will eliminate uv light and thus photosynthesis.

This weed is not easy to control. It grows in areas of thin, under-fertilized turf in poor soil.
Grows in areas of thin, under-fertilized turf in poor soil.

You should test your soil. Results give pH, liming, and nutrient deficiencies.
Fertilize in the fall.

If this weed covers 50% of the lawn, you should consider lawn renovation in August. Maintain a thick stand of turf. See our publication on lawn renovation