One of the most overlooked factors which can dramatically influence the effective-ness of a given crop production chemical is spray distribution. The uniformity of the spray distribution across the boom orwithin the spray swath is an essential component to achieving maximum chemical effectiveness with minimal cost and minimal non-target contamination. There are many other factors influencing a crop production chemical’s effectiveness, such as weather, application timing, active ingredient rates, pest infestation, etc. However, an operator must become aware of spray distribution quality if maximum efficiency is expected.

Measurement Techniques

Spray distribution can be measured in different ways. Sprayer manufacturers, as well as other research and testing stations, have patternators (spray tables) which collect the spray from nozzles on a standardized or simulated boom. These patternators have a number of channels aligned perpendicular to the nozzle spray. The channels carry the spray liquid into vessels for measuring and analysis (see photo). Under controlled conditions very accurate distribution measurements can be made for nozzle evaluation and development. Distribution measurements can also take place on an actual farm or turf sprayer. For static measurements along the sprayer boom, a patternator equal or very similar to the one described earlier is placed under the boom in a stationary position. A distribution quality test gives the applicator important information about the state of the nozzles on the boom. When much more detailed information about spray quality and coverage are required, a dynamic system—spraying a tracer (dye)— can be used.

Most of the distribution measuring devices result in data points representing the sprayers boom swath uniformity. These data points can be very revealing just through visual observation. However, for comparison reasons, a statistical method is widely accepted. This method is Coefficient of Variation (Cv). The Cv compiles all the patternator data points and summarizes them into a simple percentage, indicating the amount of variation within a given distribution. For extremely uniform distributions under accurate conditions, the Cv can be ² 7%. In some countries nozzles must conform to very strict Cv specifications and others require the sprayer’s distribution to be tested for uniformity every one or two years. These types of stipulations emphasize the importance of distribution quality

Factors Affecting Distribution

There are a number of factors contributing to the distribution quality of a spray boom or resulting Cv percentage. During a static measurement the following factors can significantly affect the distribution.

• Nozzles
  -type
  -pressure
  -spacing
  -spray angle
  -offset angle
  -spray pattern quality
  -flow rate
  -overlap
• Boom Height
• Worn Nozzles
• Pressure Losses
• Plugged Filters
• Plugged Nozzles
• Plumbing Factors Influencing Liquid Turbulence at Nozzle

Additionally, in the field during the spraying application or during a dynamic distribution test, the following can influence the distribution quality:

• Boom Stability
  -vertical movement (pitch)
  -horizontal movement (yaw)
• Environmental Conditions
  -wind velocity
  -wind direction
• Pressure Losses (sprayer plumbing)
• Sprayer Speed and Resulting Turbulence

The effect of distribution uniformity on the efficiency of a crop production chemical can vary under different circumstances. The crop production chemical itself can have dramatic influences over its efficiency. Always consult the manufacturer’s chemical label or recommendation before spraying.