Broadcast applications by helicopter, and in some cases backpack sprayer or ground equipment, can be the most effective and often least costly way to cover steep ground or tall vegetation. Uniform applications of precise herbicide rates per acre can result in good vegetation control during site preparation and safe conifer release with minimal injury potential.
Timing is critical for both site preparation and conifer release. Most site preparation occurs during the growing season at times when conifers are growing and can be injured. Site preparation herbicides like glyphosate, imazapyr, metsulfuron and aminopyralid are applied mid-summer through fall often mixed with soil residuals like sulfometuron, indaziflam or Cleantraxx. Conifers are sensitive when actively growing and release treatments are limited to lower rates of products when they are dormant before budbreak in the spring or after budset in the fall. Glyphosate, triclopyr, 2,4-D, imazapyr, clopyralid and at times soil residuals like atrazine or sulfometuron can be applied in relative safety to trees.
Calibrated spray equipment is necessary for effective and legal rate applications as listed on the label. Helicopters are often adjusted by the spray contractor. Backpack sprayers using booms or waving wand methods and ground based spray rigs with booms or boomless nozzles also need calibration to provide effective weed control and safe release treatments over conifers. Many herbicide products also stipulate the drop sizes that need to be sprayed by the equipment based on the volume median diameter (VMD). Coarse and extremely coarse droplets are specifically defined and are often mandated for certain herbicide products for both air and ground applications. Users should carefully read the labels of the product in use and adjust nozzles as needed to achieve the required size.