Pesticides are especially dangerous when improperly handled, applied, or disposed. Two general types of herbicides are effective in controlling grasses and broadleaf weeds. Pre-emergence herbicides are soil applied. They control weeds by inhibiting seed germination and development. Post-emergence herbicides are applied to green foliage where the herbicide is absorbed and translocated throughout the plant.
Some herbicides exhibit both soil and foliage activity.
Each herbicide label lists tree species registered for application, application rate dependent on soil condition, and weed species controlled. A herbicide may be labeled for a specific species of trees, like white pine or red oak, yet lack labeling for a very similar tree species. This may be due to a number of reasons. The most obvious reason is a known negative effect the herbicide has on the tree species. Another may be that research data supporting the herbicide's use on a particular tree species may be lacking.