Low-Loss-Spray-Application - The Scientific Basis

Abstract

Limited time frames caused by infection threat and weather demand for efficient pesticide application techniques in modern integrated and organic fruit farming. This demand is best complied by low volume spraying, since it minimizes traveling time and number of fillings per spray treatment, but also minimizes the probability of a contamination of the operator with concentrated pesticides. To obtain good spray deposition, low volume spray application demands small droplets which offer numerous benefits, but also carry a high drift potential. This feature threatened the technique, because no method for spray drift reduction has been available in order to make use of reduced buffer zones to water courses and non-target areas. A new method based on cross flow characteristics of the sprayer fan, canopy adapted forward speed and fan speed and a mixed set of hollow cone nozzles and air induction nozzles resulted in an approx. 85% reduction of particle drift deposits, so that the method has been registered in the official German list of drift reducing devices in the 75% drift reduction class. Besides drift reduction a canopy adapted fan speed also results in an enormous reduction of fuel consumption and noise emission as further environmental benefits of small droplets. An assessment of the influence of a canopy adapted forward speed and fan speed on spray deposit, relative spray coverage and droplet deposit density revealed a significant increase of the application efficiency, rising with decreasing canopy width and compensating a reduction of water volume and dose rate from canopy related dosing models. Testing a tower sprayer in orchards for use with reduced fan speed unexpectedly showed an unusable vertical air distribution. Alarmed by this finding, a subsequent testing of various fan types on a test bench disclosed a very unsatisfying vertical air distribution of many fan types and even within a production series the air distribution differed enormously. Especially an uneven horizontal reach of the air stream over working height is a major obstacle for a successful use of canopy adapted fan speed with all its benefits. Since a uniform vertical air distribution is the basic requirement for a highly efficient and environmentally safer spray application not only in terms of the potential to reduce pesticide consumption, but also for reducing fuel consumption and noise emissions, testing and adjusting fans of orchard sprayers on a test bench is urgently needed. Because of the importance of the topic, three fruit growers associations in Austria, Italy and Germany together initiated the development of a new test bench to measure vertical air distribution of orchard sprayers.