I stole this recent post from one of our excellent weed science specialists, Eric Prostko. It is nice to have folks like Eric and our other specialist so we can get good timely information out to our growers.
When applying contact herbicides droplet size is very important. For growers it is important to use a nozzle/pressure combination that produces COARSE droplets (VMD50 = ≥ 270 microns). Examples of contact herbicides would be: Basagran (bentazon), Cobra (lactofen), Gramoxone (paraquat), Liberty (glufosinate), and Reflex (fomesafen).
COARSE droplets provide a reasonable balance of drift protection and coverage. Droplets larger than coarse provide better drift protection but less coverage. Coverage is extremely important for contact herbicides especially when application conditions are not favorable (large weeds, cold temperatures, drought). Various nozzle types and pressures can be used to obtain COARSE droplet sizes. If you are unsure of the droplet size produced by your nozzle and the pressure you run use the chart provided by the manufacturer. Below is a chart from Green Leaf Tech. Note the combinations of nozzle and pressure resulting in coarse droplets is purple.
