Can High-Risk Fungicides be Used in Mixtures Without Selecting for Fungicide Resistance?

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.

Emergence and early evolution of fungicide resistance in North American populations of Zymoseptoria tritici

“…However, they may be able to control how rapidly resistance emerges in their local populations through careful and dynamic management of fungicide applications. In particular, they should always use fungicide mixtures and also use the lowest possible fungicide doses that can provide a desirable level of disease control (Mikaberidze et al, 2014). Figure S1.…”

Occurrence of Cercospora beticola populations resistant to benzimidazoles and demethylation-inhibiting fungicides in Serbia and their impact on disease management

“…A mixture of DMI and QoI fungicides is very effective at controlling C. beticola and might serve as an exceptional solution at localities with high frequencies of resistant populations. Mikaberidze et al (2013) proposed that if fitness costs are absent, then the use of high-risk fungicides in a mixture selects for resistance, and the fungicides eventually become non-functional. If there is a cost of resistance, then a mixture harboring an optimal ratio of fungicides can be developed, in which selection for resistance is expected to vanish and the level of disease control can be optimized.…”

Resistência cruzada aos fungicidas IQo azoxistrobina e piraclostrobina no patógeno da brusone do trigo Pyricularia oryzae no Brasil

“…Sob o ponto de vista do manejo da resistência a fungicidas, Mikaberidze et al (20) propuseram que o custo adaptativo da resistência à fungicidas para as populações de fitopatógenos é um parâmetro crucial para determinar o resultado da competição entre as estirpes sensíveis e resistentes do patógeno e para avaliar a utilidade da mistura de fungicidas. Se não houver custo adaptativo, mesmo a utilização do fungicida de alto risco em mistura pode selecionar o fitopatógeno para resistência e, eventualmente, o fungicida de alto risco se torna não funcional.…”