Effect of application method on the control of powdery mildew (Bulmeria graminis) on spring barley

Two field experiments were conducted to establish the effect spray application parameters have on the response of barley powdery mildew to fungicides. Measurements of the distribution of spray deposit within and below the plant canopy were carried out during both experiments using techniques based on the fluorescent tracer Tinopal. The volume deposited was determined by fluorescence spectrometry and the surface coverage was determined by image analysis. To remove the influence of application volume and formulation concentration, all treatments were made at 200 l/ha. In the first experiment three chemicals with differing modes of action, sulfur, prochloraz, and epoxiconazole, were used. Their intrinsic fungal pathogenicity was determined using a laboratory bioassay technique. The control of mildew by the chemicals was found to be significantly altered by nozzle type. Sprays classified under the BCPC scheme as fine and medium provided more disease control at full and half dose compared to a coarse spray and an air-included very coarse spray. In the second experiment, the influence of nozzle type on the field dose response of epoxiconazole was determined. The coefficient of variation of spray coverage was the only factor that provided a significant correlation between biological response and spray deposit. This demonstrated the significance of application method for controlling fungal pathogens, particularly at reduced dose, and highlighted the importance of uniform coverage for achieving control. (C) 2003 Elsevier Science Ltd. All rights reserved.