Effect of nozzle type and pressure on the efficacy of spray applications of the bioherbicidal fungus Microsphaeropsis amaranthi

The effect of application technology on efficacy has been thoroughly investigated for sprays of chemical pesticide but not biological pesticides. This study investigates the effect of applying conidia of Microsphaeropsis amaranthi, a candidate bioherbicide for Amaranthus spp., with a range of different hydraulic nozzle tips. The nozzle tips were selected to deliver sprays with different spectra of droplet sizes deployed at different angles. We found that sprays of large droplets gave poor coverage of the target and resulted in low levels of disease severity on common waterhemp. The most effective nozzle tip tested was a hollow cone nozzle tip, such as is commonly used for the application of fungicides. This nozzle tip deployed large numbers of fine droplets that swirled within the plant canopy, provided good coverage of all plant parts, and resulted in the highest levels of disease severity, particularly on stems. Nomenclature: Common waterhemp, Amaranthus rudis Sauer, #(3) AMATA. Additional index words: Bioherbicide, application technology, biological control. Abbreviations: AI, air induction spray tip TeeJet (R) AI 11004; flat fan, standard flat spray tip TeeJet (R) TP 110015; full cone, full cone spray tip TeeJet (R) TG-4; hollow cone, hollow cone spray tip TeeJet (R) TX-8 Conejet; XR, extended range flat spray tip TeeJet (R) XR 11001; VMD, volume mean diameter: 50% of the spray volume composed of droplets larger, and 50% of the spray volume composed of droplets smaller, than the VMD.