As the frequency of fungicide resistant strains increases in a pathogen population, there is a change in the shape of the response curve of disease severity to fungicide dose. We showed previously, in a theoretical analysis, that such changes can result in an increase or a decrease in the economically optimal dose of fungicide; this depends on how the response curve changes (which is determined jointly by the degree of insensitivity and frequency of a new strain) and the shape of the disease–yield loss relationship (which is a characteristic of the pathogen and crop). Here, we use field dose–response data to estimate economic optimum doses for the control of Zymoseptoria tritici on wheat over a 21‐year period. Resistance to fungicide developed to varying degrees against three modes of action (MoA). Changes of optimal dose across years differed according to MoA, but there was an underlying pattern of initial increase in optimal dose, followed by a decrease (ultimately to zero dose at high levels of fungicide resistance). Fungicides are often applied in mixture and analysis shows that, provided the mixture partner is effective, the economic optimal dose increases less as resistance develops than when the fungicide is used as solo product; however, the subsequent decrease in optimal dose remains.

中文翻译：

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随着抗药性的发展，确定何时增加或减少杀菌剂剂量对经济有利：来自长期田间试验的评估

随着病原体群体中杀菌剂抗性菌株的频率增加，疾病严重程度对杀菌剂剂量的响应曲线的形状发生了变化。我们之前在理论分析中表明，这种变化会导致杀菌剂的经济最佳剂量增加或减少；这取决于响应曲线如何变化（由新菌株的不敏感程度和频率共同决定）以及疾病-产量损失关系的形状（这是病原体和作物的特征）。在这里，我们使用田间剂量-反应数据来估计在 21 年期间控制小麦上的 Zymoseptoria tritici 的经济最佳剂量。对三种作用方式 (MoA) 的杀菌剂产生不同程度的抗性。根据农业部的不同，最佳剂量随年份的变化有所不同，但存在一种潜在的模式，即最佳剂量最初增加，然后减少（在高杀菌剂抗性水平下最终降至零剂量）。杀菌剂通常以混合物形式使用，分析表明，如果混合物伙伴有效，与杀菌剂单独使用相比，随着抗药性的发展，经济最佳剂量增加的幅度较小；然而，随后最佳剂量的降低仍然存在。与杀菌剂单独使用时相比，随着抗药性的发展，经济最佳剂量增加得更少；然而，随后最佳剂量的降低仍然存在。与杀菌剂单独使用时相比，随着抗药性的发展，经济最佳剂量增加得更少；然而，随后最佳剂量的降低仍然存在。