The Lektraspray Nozzle: A novel ultra low volume spray applicator for the greenhouse industry

Abstract

A novel electrostatic spray nozzle, termed the Lektraspray Nozzle, was evaluated to assess its suitability for pesticide application in the greenhouse industry. The nozzle is based on the vortical nozzle principle, releasing the spray liquid into a low pressure/high volume airstream through a flexible emitter tube. The encompassing airstream shatters the liquid into small droplets and transports them to the target. The experimental work identified that the nozzle could deliver a droplet spectra with a Volume Median Diameter (VMD) of approximately 75 μm for a range of liquids and viscosities. Charging the droplets had a minor effect on the VMD, although typically improved the droplet spectra. The nozzle could be operated satisfactorily with or without electrostatically charging the droplets. The VMD could be changed simply by increasing/decreasing the liquid flow rate and/or adjusting the air pressure of the encompassing airstream. Small adjustments to the air pressure (4.5 to 14 kPa) will allow the production of an acceptable droplet spectra over a large range of liquid flow rates (30 to 1000 ml/min). The results of a limited number of tests using the Lektraspray nozzle on plants indicated that electrostatic charging could significantly influence the deposition of droplets on the underside of the leaves, providing the foliage was not "dense". However no significant increase in the total amount deposited on the plant was noted when the droplets were charged. The results from spraying a "dense" foliage plant (Pittosporum eugenioides) indicated the need to adjust the charge/air pressure relationship of the spray nozzle to increase underleaf deposition and improve droplet penetration into the plant canopy. After evaluating the experimental work on the Lektraspray nozzle, and considering the simplicity and ruggedness of the nozzle, the conclusion was that it should be seriously considered as an alternative spray application technique for use where controlled environment spraying is required. In particular - the greenhouse industry.