Using epidemiological principles to explain fungicide resistance management tactics: Why do mixtures outperform alternations?
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Whether fungicide resistance management is optimized by spraying chemicals with different modes of action as a mixture (i.e., simultaneously) or in alternation (i.e., sequentially) has been studied by experimenters and modelers for decades. However, results have been inconclusive. We use previously parameterized and validated mathematical models of wheat Septoria leaf blotch and grapevine powdery mildew to test which tactic provides better resistance management, using the total yield before resistance causes disease control to become economically ineffective (“lifetime yield”) to measure effectiveness. We focus on tactics involving the combination of a low-risk and a high-risk fungicide, and the case in which resistance to the high-risk chemical is complete (i.e., in which there is no partial resistance). Lifetime yield is then optimized by spraying as much low-risk fungicide as is permitted, combined with slightly more high-risk fungicide than needed for acceptable initial disease control, applying these fungicides as a mixture. That mixture rather than alternation gives better performance is invariant to model parameterization and structure, as well as the pathosystem in question. However, if comparison focuses on other metrics, e.g., lifetime yield at full label dose, either mixture or alternation can be optimal. Our work shows how epidemiological principles can explain the evolution of fungicide resistance, and also highlights a theoretical framework to address the question of whether mixture or alternation provides better resistance management. It also demonstrates that precisely how spray tactics are compared must be given careful consideration.
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Oliver, Richard (2016)Evolved resistance to fungicides is a critical issue for global food security. Resistance has emerged rapidly in some cases, and some so it is vital that the effective life of actives is prolonged as much as practicable. ...
Van Den Bosch, F.; Paveley, N.; Van Den Berg, F.; Hobbelen, P.; Oliver, Richard (2014)We have reviewed the experimental and modeling evidence on the use of mixtures of fungicides of differing modes of action as a resistance management tactic. The evidence supports the following conclusions. 1. Adding a ...
The usefulness of fungicide mixtures and alternation for delaying the selection for resistance in populations of mycosphaerella graminicola on winter wheat: A modeling analysisHobbelen, P.; Paveley, N.; Oliver, Richard; van den Bosch, F. (2013)A fungicide resistance model (reported and tested previously) was amended to describe the development of resistance in Mycosphaerella graminicola populations in winter wheat (Triticum aestivum) crops in two sets of fields, ...