All of the plants that are found in your lawn are either monocots (grasses) or dicots (broadleafs). Most herbcides used for weed control in home lawns are designed to control dicot weeds such as dandelion, and plantains. Trees and shrubs are in the same phylum (group) as the weeds and can be injured by broadleaf herbicides.
Most herbicides designed to control dicot weeds are primarily absorbed through the leaves, but some are also absorbed through the roots. Dicamba, in particular, is potentially damaging to trees and shrubs via root uptake. Apply your herbicides according to label directions, carefully avoiding foliage contact, drift, and/or volitalization.
