title: Delaying selection for fungicide insensitivity by mixing fungicides at a low and high risk of resistance development: a modeling analysis.
abstract: This study used mathematical modeling to predict whether mixtures of a high-resistance-risk and a low-risk fungicide delay selection for resistance against the high-risk fungicide. We used the winter wheat and Mycosphaerella graminicola host-pathogen system as an example, with a quinone outside inhibitor fungicide as the high-risk and chlorothalonil as the low-risk fungicide. The usefulness of the mixing strategy was measured as the "effective life": the number of seasons that the disease-induced reduction of the integral of canopy green area index during the yield forming period could be kept <5%. We determined effective lives for strategies in which the dose rate (i) was constant for both the low-risk and high-risk fungicides, (ii) was constant for the low-risk fungicide but could increase for the high-risk fungicide, and (iii) was adjusted for both fungicides but their ratio in the mixture was fixed. The effective life was highest when applying the full label-recommended dose of the low-risk fungicide and adjusting the dose of the high-risk fungicide each season to the level required to maintain effective control. This strategy resulted in a predicted effective life of ≤ 12 years compared with 3 to 4 years when using the high risk fungicide alone.
authors.affiliation: Rothamsted Research, Harpenden, UK. peter.hobbelen@rothamsted.ac.uk
authors.forename: P H F
authors.initials: PH
authors.lastname: Hobbelen
authors.forename: N D
authors.initials: ND
authors.lastname: Paveley
authors.forename: F
authors.initials: F
authors.lastname: van den Bosch
mesh_terms: D001203:Ascomycota / Q000187:drug effects* / Q000254:growth & development; D003198:Computer Simulation; D025141:Drug Resistance, Fungal / Q000187:drug effects*; D005659:Fungicides, Industrial / Q000494:pharmacology*; D008962:Models, Theoretical; D010935:Plant Diseases / Q000382:microbiology*; D012621:Seasons; D012641:Selection, Genetic / Q000187:drug effects; D014908:Triticum / Q000382:microbiology*
chemical_list: D005659:Fungicides, Industrial