Effects of spraying volume and chemical rate on the control of apple scab ( Venturia inaequalis) and codling moth ( Cydia pomonella) in an apple orchard

Abstract

A spray programme on small apple trees heavily infested with codling moth and apple scab compared the effectiveness of 1000 l/ha and 200 l/ha at each of 100%, 75%, and 50% of the recommended rates of azinphos-methyl (insecticide) and bitertanol (fungicide). The higher spray volume rate was applied with a high volume of air at low airspeed. The lower volume rate was applied using an airblast sprayer delivering a low volume of air at high airspeed and electrostatically charged droplets. The chemical rate did not affect the level of control of either organism. Control of codling moth was significantly better at the higher (0 · 9% of fruits infested) than at the lower volume rate (2 · 4%); 20 · 3% of fruits in the control were infested. The percentage of fruit infected with apple scab was lowest at the high volume rate (8 · 8%), significantly higher at the lower volume rate (27 · 9%), and higher again on the control (52 · 8%). The failure to control apple scab at the low volume rate may be due to the volume rate per se or to droplet size influencing the amount of bitertanol absorbed into the leaf.