Effect of planting dates and azoxystrobin fungicide application regimes on common rust of maize

Abstract

A study over two growing seasons evaluated the efficacy and cost effectiveness of azoxystrobin (Amistar® SC), applied at different action thresholds and plant growth stages, on the incidence and severity of common rust of maize grown in the Pukekohe, New Zealand. Azoxystrobin applied as a preventative before disease symptoms appeared, or at the onset of disease symptoms, gave equal or better control than fungicide applications applied at 3% and 6% rust thresholds. However, using a 3% disease threshold up to the tasselling stage to time the application of azoxystrobin, controlled common rust in the more severe rust season (2008–09) and saved fungicide application costs associated with preventative (calendar) or disease-onset applications of azoxystrobin in the less severe rust season (2007–08) when the rust levels did not reach 3% by the tasselling stage. The maize hybrid 34D71 used was classified as moderately susceptible to common rust and, from the research presented here, it appears that although azoxystrobin applications reduced common rust severity, the lack of yield gains suggests that azoxystrobin applications in northern New Zealand may be economic only when growing highly susceptible maize varieties.