Sensitivity of Podosphaera aphanis isolates to DMI fungicides: distribution and reduced cross-sensitivity.
BACKGROUND
Management of strawberry powdery mildew, Podopshaera aphanis (Wallr.), requires numerous fungicide treatments. Limiting epidemics is heavily dependent on sterol demethylation inhibitors (DMIs) such as myclobutanil or penconazole. Recently, a noticeable reduction in the efficacy of these triazole fungicides was reported by strawberry growers in France. The goal of this study was to investigate the state of DMI sensitivity of French P. aphanis and provide tools for improved pest management.


RESULTS
Using leaf disc sporulation assays, sensitivity to myclobutanil and penconazole of 23 isolates of P. aphanis was monitored. Myclobutanil EC(50) ranged from less than 0.1 to 14.67 mg L(-1) and for penconazole from 0.04 to 4.2 mg L(-1). A cross-analysis and a Venn diagram showed that there was reduced sensitivity and a positive correlation between the less sensitive myclobutanil and penconazole isolates; 73.9% of isolates were less sensitive to a DMI and 47.8% exhibited less sensitivity to both fungicides.


CONCLUSIONS
The results show that sensitivity to myclobutanil and, to a lesser extent, penconazole has become less efficient in strawberry powdery mildew in France. Therefore, urgent action is required in order to document its appearance and optimise methods of control.
Sombardier
Audrey
A
INRA, UMR Santé Végétale, Villenave d'Ornon, France.
Dufour
Marie-Cécile
MC
Blancard
Dominique
D
Corio-Costet
Marie-France
MF
D001203:Ascomycota / Q000187:drug effects*; D026141:Drug Resistance, Multiple, Fungal; D031985:Fragaria / Q000382:microbiology; D005659:Fungicides, Industrial / Q000494:pharmacology; D009570:Nitriles / Q000494:pharmacology*; D010935:Plant Diseases / Q000382:microbiology; D014230:Triazoles / Q000494:pharmacology*
D005659:Fungicides, Industrial; D009570:Nitriles; D014230:Triazoles; C087058:penconazole; C446685:systhane