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Title: Effects of water hardness on spray droplet size under aerial application conditions

item Hoffmann, Wesley
item Fritz, Bradley - Brad
item Lan, Yubin
item Martin, Daniel - Dan

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/20/2007
Publication Date: 2/10/2008
Citation: Hoffmann, W.C., Bagley, W.E., Fritz, B.K., Lan, Y., Martin, D.E. 2008. Effects of water hardness on spray droplet size under aerial application conditions. Applied Engineering in Agriculture. 24(1):11-14.

Interpretive Summary: Water hardness due to calcium and magnesium compounds can significantly affect droplet size and material efficacy of crop protection sprays. This study compared effects of water hardness and chemical additives (adjuvants) on droplet size produced by two commonly-used spray nozzles under aerial application conditions. Adjuvants mixed in a tank solution decreased droplet size when water hardness exceed 200 parts per million, which could lead to an increase in spray drift. Aerial applicators should test for water hardness before mixing adjuvants in a tank solution, and use caution when the water hardness exceeds 200 parts per million.

Technical Abstract: Minerals and organic matter in spray carrier water can reduce the effectiveness of some plant protection products. Water hardness has been found to have a significant impact of the efficacy of some crop protection materials and has shown conflicting influence on spray droplet size. The objectives of this study were to determine the effects of water hardness on spray droplet size produced by two commonly used spray nozzles with and without the addition of an invert suspension adjuvant to the tank solution under aerial application conditions. Water hardness levels from 0-800 ppm and/or the addition of a spray adjuvant to a spray solution had a significant effect on spray droplet size. The spray adjuvant, an invert suspension, increased most spray droplet size parameters and decreased the percent of spray volume contained in droplets less than 200 microns as long as the water hardness did not exceed 200 ppm. The spray adjuvant had little or a negative effect on relative span under high liquid shear sprays (Treatment 1) but lowered the relative span for sprays orientated 0 degrees to the high speed airstream. Aerial applicators should test the water used in making tank solution for water hardness before the addition of spray adjuvants and use caution when the water hardness exceeds 200 ppm.