Can high risk fungicides be used in mixtures without selecting for fungicide resistance?

TL;DR

This study uses a population dynamics model to evaluate whether combining high-risk fungicides with low-risk ones in mixtures can control disease effectively without promoting resistance, emphasizing the importance of resistance fitness costs.

Contribution

The paper introduces a model analyzing how fitness costs influence resistance development in fungicide mixtures, guiding optimal fungicide ratios to prevent resistance.

Findings

Fitness costs are crucial for resistance management.

Optimal fungicide ratios can prevent resistance selection.

Without fitness costs, resistance inevitably develops.

Abstract

Fungicide mixtures produced by the agrochemical industry often contain low-risk fungicides, to which fungal pathogens are fully sensitive, together with high-risk fungicides known to be prone to fungicide resistance. Can these mixtures provide adequate disease control while minimizing the risk for the development of resistance? We present a population dynamics model to address this question. We found that the fitness cost of resistance is a crucial parameter to determine the outcome of competition between the sensitive and resistant pathogen strains and to assess the usefulness of a mixture. If fitness costs are absent, then the use of the high-risk fungicide in a mixture selects for resistance and the fungicide eventually becomes nonfunctional. If there is a cost of resistance, then an optimal ratio of fungicides in the mixture can be found, at which selection for resistance is expected to vanish and the level of disease control can be optimized.