Articles
Fungicide insensitivity of Stemphylium vesicarium isolates from the Holland Marsh, Ontario to azoxystrobin and fluopyram in 2020
Article number
1398_16
Pages
117 – 124
Language
English
Abstract
Stemphylium vesicarium, the causal agent of Stemphylium leaf blight (SLB) is an important fungal pathogen of onion (Allium cepa) in North America.
SLB reduces yield and quality though premature defoliation and reduces sprouting inhibition in storage.
No onion cultivars are resistant to S. vesicarium, so management of SLB relies on frequent application of foliar fungicides.
Unfortunately, fungicide efficacy against SLB has declined in recent years, likely because of fungicide insensitivity.
A recent study in New York showed that S. vesicarium on onion was insensitive to fungicides in FRAC groups 3, 7, 9 and 11. A previous study of isolates from onion in the Holland Marsh, Ontario reported that insensitivity to azoxystrobin (FRAC 11) at 5 μg a.i. mL‑1 increased from zero (all sensitive) in isolates collected in 2012 to 94% in 2018 and 2019. Insensitivity to fluopyram has progressed with a single isolate collected in 2012 sensitive to fluopyram (FRAC 7) increasing to 100% of isolates collected in 2018 and 2019 insensitive to 10 ppm fluopyram.
In the current study, the sensitivity of S. vesicarium isolates collected from the Holland Marsh in 2020 to azoxystrobin and fluopyram was assessed.
Insensitivity to azoxystrobin and fluopyram increased to 100% in 2020. As a result, fungicides containing azoxystrobin or fluopyram are no longer recommended for SLB management on onion in the Holland Marsh.
Studies of other fungicides registered for use on onion are in progress to monitor changes in sensitivity and to establish baseline sensitivity levels for new fungicides.
SLB reduces yield and quality though premature defoliation and reduces sprouting inhibition in storage.
No onion cultivars are resistant to S. vesicarium, so management of SLB relies on frequent application of foliar fungicides.
Unfortunately, fungicide efficacy against SLB has declined in recent years, likely because of fungicide insensitivity.
A recent study in New York showed that S. vesicarium on onion was insensitive to fungicides in FRAC groups 3, 7, 9 and 11. A previous study of isolates from onion in the Holland Marsh, Ontario reported that insensitivity to azoxystrobin (FRAC 11) at 5 μg a.i. mL‑1 increased from zero (all sensitive) in isolates collected in 2012 to 94% in 2018 and 2019. Insensitivity to fluopyram has progressed with a single isolate collected in 2012 sensitive to fluopyram (FRAC 7) increasing to 100% of isolates collected in 2018 and 2019 insensitive to 10 ppm fluopyram.
In the current study, the sensitivity of S. vesicarium isolates collected from the Holland Marsh in 2020 to azoxystrobin and fluopyram was assessed.
Insensitivity to azoxystrobin and fluopyram increased to 100% in 2020. As a result, fungicides containing azoxystrobin or fluopyram are no longer recommended for SLB management on onion in the Holland Marsh.
Studies of other fungicides registered for use on onion are in progress to monitor changes in sensitivity and to establish baseline sensitivity levels for new fungicides.
Publication
Authors
E. McFaul, B.D. Gossen, M.R. McDonald
Keywords
fungicide insensitivity, onion, stemphylium leaf blight, crop protection, disease management
Groups involved
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