Spatial and temporal impact of fungicide spray strategies on fungicide sensitivity of Mycosphaerella graminicola in winter wheat

Abstract

Field experiments, involving various fungicide strategies with pyraclostrobin and/or epoxiconazole were carried out in 2004 and 2005, with the overall purpose of monitoring the evolution of fungicide sensitivity in Mycosphaerella graminicola on different isolates per leaf, leaf levels at different points of time, and points in the field. Sensitivity was assessed on single isolates by means of epoxiconazole EC 50 -values, and monitoring of the G143A-mutation, which confers strobilurin resistance. In both years, fungicide application strategies did not cause any significant shifts in epoxiconazole sensitivity of the population median or variance over time compared to the starting population. In 2004, the end-population median was the same for all sprayed strategies, although compared to untreated median sensitivities were higher. In 2005, epoxiconazole sensitivity levels were similar on individual flag leaves and different points in the field. Measured on all isolates the EC 50 -values ranged from 0.007-1.15 mg l −1 . In 2004, due to the high initial level of pyraclostrobin resistance, stabilisation of pyraclostrobin resistance was observed following the various combination treatments. No correlation between epoxiconazole sensitivities and pyraclostrobin resistance were observed. High input strategies using a mixture of epoxiconazole and pyraclostrobin resulted in the best control and yield response. A subpopulation of the isolates from 2004 was also screened for sensitivity towards five different triazoles of which tebuconazole proved to be least sensitive, and this could further be split into two subpopulations.

Fungicide resistance: facing the challenge - a review

“…In this case one "at risk" opposes selection against the other. Although a recent modelling exercise showed that a mixture of two high resistance risk partners enhanced the life of both fungicides (Hobbelen et al 2013), experimental evidence supporting use of just "at risk" partners is limited to a few studies ((Brent et al 1989;Lorenz et al 1992;Gisi et al 2005;Thygesen et al 2009). …”

The Emergence of Resistance to Fungicides

“…However, in many of these studies resistant strains were either introduced [4], [6], [13] or were already present at a significant frequency at the start of experiments [7], [9], [14]. As even a frequency of 1% represents a large population of resistant lesions, these studies describe the selection phase in the evolution of fungicide resistance.…”

A time‐course investigation of resistance to the carboxylic acid amide mandipropamid in field populations of Plasmopara viticola treated with anti‐resistance strategies

“…Berlese and De Toni . However, the repeated use of a particular fungicide class is not always associated with a decreased sensitivity . This creates a complex scenario, which is usually approached at the theoretical level to establish a relationship between fungicide spray programs and the possible evolution of resistance in the field …”

“…5,6 However, the repeated use of a particular fungicide class is not always associated with a decreased sensitivity. 7,8 This creates a complex scenario, which is usually approached at the theoretical level to establish a relationship between fungicide spray programs and the possible evolution of resistance in the field. [9][10][11][12] To date, no multi-year studies on the dynamics of pathogen populations in real field conditions, where single-site fungicides are applied according to anti-resistance criteria, are available.…”