How to stop drift before it floats away! Part 3 Back »

“If label recommendations for tip usage are not followed, drift and misapplication will surely follow.”

The goals of applying any crop protection products include increasing effectiveness, and maximizing profits all while mitigating drift. Weather is the primary factor influencing drift, including wind (direction and speed), temperature, humidity and air stability/inversions. Their impacts are covered in Part 1. Best sources for weather data was covered in Part 2. This article will focus on mitigating drift through nozzle tip selection.

Nozzle Selection

Industry today has more nozzle options designed to reduce drift, improve droplet size control, and an emphasize spray quality than ever before. Nozzle tips are important to control the rate of product delivered, determine uniformity of application, affects the coverage, and influences the drift potential. Always refer to the product label for nozzle tip recommendations.

Spray Droplet Size
The effectiveness of the product and drift potential is influenced by the size of the spray droplets and droplet spectrum. Spray droplet volume median diameter (VMD) is measured in microns (1 micron = 1/25,000 inch). To give everyday examples of approximate diameters of items, a pencil lead is 2000 microns, a paper clip is 850 microns, a staple is 420 microns, a toothbrush bristle is 300 microns, a sewing thread is 150 microns, and a human hair is around 100 microns. When selecting nozzle tips to use you will have options ranging from extremely fine to ultra coarse (Table 1).

Spray Coverage
Spray droplet size also influences spray coverage. As spray droplet size increases, spray coverage decreases. As a rule of thumb select nozzles, tip sizes, and operating pressures that produce large enough spray droplets that reduce the risk of drift, while giving adequate coverage for the pesticide type used. Spray droplets less than 200 microns in diameter are light, and remain airborne a long time and are most prone to drift.

Table 1. Spray droplet categories and volume mean diameters.

VMD (Microns)
Extremely Fine
≈ 50
Very Fine
Very Coarse
Extremely Coarse
Ultra Coarse
Data Source: America Society of Agricultural & Biological Engineers (ASABE) S-572, March 2013

Application Considerations

Keep these strategies in mind when planning to spray:

  • Select the correct nozzle for the product to increase droplet size and decrease spray fines.
  • Increase flow rates, higher application volumes.
  • Use lower pressures.
  • Use lower spray boom heights.
  • Avoid adverse weather conditions.
  • Consider using buffer zones.
  • Consider using new technologies (e.g. drift reduction nozzles, drift reduction additives, shields).

Herbicides are only a tool, we must keep in mind the three ways to slow weed issues are; competition, sanitation, and rotation.

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