Abstract

This paper compares two previously established meteorological modelling methods when determining areas in Western Australia (WA) where conditions are favourable for infection of wheat (Triticum aestivum) by Tilletia indica, the cause of Karnal bunt. There was a strong correlation (r = 0.83) between the Humid Thermal Index (HTI) model, which used long-term, average-monthly data, and the rainfall model, which was based on the per cent chance of at least three Suitable Rain Events (SRE) during the susceptible period (August to October). Results suggest that northern wheat growing areas are too hot and dry (HTI < 2.2, chance of SRE 15–27%), southern areas are marginal to too cold and/or wet (HTI > 3, chance of SRE 68–97%), eastern areas are marginal to too hot and dry (HTI around 2.2, chance of SRE 24–50%), and western areas are suitable (HTI between 2.2 and 3.3, chance of SRE 41–78%). The between and within year analysis indicated that infection was more likely to occur if anthesis occurred in northern areas in August, in October in southern areas, in September in eastern areas, and in August, September, and October in western and south-eastern areas. Model results suggest that data on HTI and SRE within each year may be more accurate in determining climatic suitability for Karnal bunt in WA, compared to long-term, average data. In the event that T. indica does successfully enter WA, it may be possible to limit spread of Karnal bunt through carefully planned sowing schedules.