Four Rules of Nozzle Selection

All nozzles will give very good results, provided you use them properly.

Posted: February 16, 2006

Dr. Tom Wolf, a researcher with Agriculture and Agri-Food Canada's Saskatoon Research Centre provides a few rules to keep in mind when deciding on which nozzle to use to avoid disappointment in pesticide performance.

1. Choose the best nozzle type for your needs
   1. Conventional Flat Fan
      • Advantages: reliable performance, allows lowest water volumes
      • Disadvantages: drift prone, can't use high pressures
   2. Pre-Orifice
      • Advantages: reduce drift 50%, reliable efficacy at lower volumes, good for grassy weeds
      • Disadvantages: need slightly higher pressures than conventional flat fan
   3. Low-Pressure Air Induced
      • Advantages: reduce drift 50 to 70%, can use reasonable pressure, good for grassy weeds higher pressures or volumes
      • Disadvantages: need >5 gpa, >30 to 40 psi
   4. High Pressure Air Induced
      • Advantages: reduce drift 70 to 90%,
      • Disadvantages: must use higher pressures (>60 psi) and more water (>7 gpa) for grassy weeds

   Determine your priorities before choosing a nozzle. If you are looking for better drift control, use type b, c or d. Best pressure range? Use type b or c. Lower water volumes? Try type a or b. All nozzles will give very good results provided you use them properly.

2. Watch your water volume

   The coarser your spray, the higher your water volume must be. There are two main reasons for this. (i) you must have enough droplets per square centimetre to hit your target. This is most critical for pre-seed burnoff, where weeds are smallest, and low-volume, coarse sprays will likely miss weeds entirely. (ii) you need sufficient coverage on your target for the pesticide to do its job. This is most important for contact herbicides such as bromoxynil, glufosinate, and diquat, and for insecticides and protective fungicides. It is also important for grassy weeds, most of which have a hard time retaining very large droplets. Use at least 5 to 7 gpa for in-crop herbicides, 10 to 12 gpa for fungicides.

3. Use the right pressure for your nozzle

   The most common reason for performance complaints is when the spray pressure of a low-drift nozzle is too low, resulting in insufficient overlap between nozzles. Air-induced nozzles and some pre-orifice nozzles require higher pressures to operate properly. If your sprayer cannot produce sufficiently high pressures, you should not be using these nozzles. Try to do most of your spraying at these pressures: Conventional, 20 - 50 psi, pre-orifice, 30 - 60 psi, low-pressure air-induced, 40 to 60 psi, high pressure air-induced, 60 to 80 psi. Higher pressures increase drift, but less so for pre-orifice and air-induced nozzles.

4. Ensure good patterns

   The coarser droplets produced by low-drift sprays will go where they're pointed. There is only one chance to get uniform coverage across the boom. Finer sprays from conventional nozzles can re-distribute themselves with wind or turbulence, covering up mistakes. For coarse sprays, try to achieve a nozzle pattern width that is twice your nozzle spacing at the target height. Do this by selecting wider angle nozzles, increasing pressure, or adjusting boom height. This will ensure that the coarsest droplets at the pattern edge are mixed in with the more abundant, finer droplets found in the middle of a pattern.