A stovepipe or other protective shield may be placed around the trees while spraying to protect them from herbicide damage. With band and spot treatments the weeds between treated areas must be mowed or cultivated. Mowing between tree rows is recommended where soil erosion may occur. If you are planting trees and will make herbicide spot treatments, cross-checking the rows will make weed control within rows easier. Calibration Accurate calibration is the only way to know your actual rate of application.
Some herbicides have a narrow margin of safety between injury and effective weed control.
Calibration is necessary every time you change chemicals or application rate. Check nozzle tips for wear or changes in discharge and be sure they are clean. With power sprayers, be careful to use the proper type of nozzle. Both application rate and spray distribution will vary with changes in spray tank pressure, how high the nozzle is held and how fast it is moved over the area being treated. Special care is needed when applying selective, soil-active chemicals such as the preemergence herbicides.