Poster: Biology & Disease Mgmt: Chemical Control
Presence of fungicide resistant Botrytis strains in Norwegian forest nurseries
G. STRØMENG (1), V. Talgø (1), I. Fløistad (1) (1) NIBIO, Norway
Approximately 30 million seedlings of Norway spruce (Picea abies) are planted in Norwegian forests each year, and the main part of these plants are produced by forest nurseries in Norway. Among the greatest challenges in the seedling production is the control of gray mold, caused by Botrytis. Fungicides used in Norwegian forest nurseries to control gray mold are thiophanate methyl, fenhexamid, iprodione, and a mixture of cyprodinil and fludioxonil. Increasing disease problems in newly planted seedlings over the last few years, made it necessary to investigate the possible presence of fungicide resistant Botrytis strains in forest nurseries. Isolates were collected from spruce seedlings and germ tube growth was measured on nutrient agar amended with different concentrations of the fungicides. We tested fludioxonil and cyprodinil separately, by using fungicides that contained fludioxonil or pyrimethanil (same chemical group as cyprodinil, cross resistance expected) as single active ingredients. Thus far, we have tested 35 isolates, and 54, 26 and 6 % of these were resistant to thiophanate methyl, fenhexamid, and iprodione, respectively. Furthermore, 46, 26, 6, and 3% were moderately resistant to thiophanate methyl, pyrimethanil, iprodione, and fludioxonil, respectively. Nine isolates were resistant to two fungicides. We recommend that the nurseries avoid use of thiophanate methyl in the future, and that fenhexamid resistance is carefully monitored.