Adjusting fungicide treatment programmes when resistance is developing: The case of spot‐form net‐blotch in Western Australia

Abstract

AbstractWe use the case of spot‐form net‐blotch (SFNB) and azole fungicides in Western Australia to investigate the financial implications of a switch from fungicide A, to which high resistance is developing, to a more expensive fungicide B, to which less resistance has developed. This is done using a budget calculation coupled with an epidemiological model. The model calculates the total financial cost of disease as the sum of the expense of the fungicide treatment programme and the cost of disease‐induced yield loss. The optimal treatment programme is that which minimizes the total cost of disease. We show that when the pathogen population is dominated by wild‐type strains, propiconazole is the fungicide minimizing the cost of disease. The number of applications and optimal dose depend on the potential yield of the field under consideration. When the pathogen population is dominated by a strain highly resistant to propiconazole, the use of this fungicide will not give a positive financial return. In this case the azole mixture, prothioconazole + tebuconazole is more cost effective. The pathogen strains with medium resistance to propiconazole have little effect on the optimal treatment programme compared to the wild type. We also use the model to calculate, depending on the potential yield and on whether an effective seed treatment is used, the frequency of the highly resistant strains at which the switch from the use of propiconazole to the use of prothioconazole + tebuconazole is economically justified.