Do growers using solo fungicides affect the durability of disease control of growers using mixtures and alternations?: The case of spot-form net-blotch in Western Australia

Abstract

Growers often use alternations or mixtures of fungicides to slow down the development of resistance to fungicides. However, within a landscape some growers will implement such resistance management methods while others do not, and may even apply solo components of the resistance management programme. We investigated whether growers using solo components of resistant management programmes affect the durability of disease control in fields of those who implement fungicide resistance management. We developed a spatially implicit semi-discrete epidemiological model for the development of fungicide resistance. The model simulates the development of epidemics of spot-form net-blotch disease, caused by the pathogen Pyrenophora teres f. maculata. The landscape comprises three types of fields, grouped according to their treatment programme, with spore dispersal between fields early in the cropping season. In one field type a fungicide resistance management method is implemented, while the two others do not, with one of these field types using a component of the fungicide resistance management programme. The output of the model suggests that the use of component fungicides does affect the durability of disease control for growers using resistance management programmes. The magnitude of the effect depends on the characteristics of the pathosystem, the degree of inoculum mixing between fields, and the resistance management programme being used. Additionally, while increasing the amount of the solo component in the landscape generally decreases the lifespan within which the resistance management programme provides effective control, situations exist where the lifespan may be minimized at intermediate levels of the solo component fungicide.