Page 128 - PC2019 Program & Proceedings

PLANT CANADA 2019

S41. Ferrous sulfate reduces dollar spot disease on different cultivars of creeping bentgrass
*
Rudland, M. ; T. Hsiang; V. Forte-Perri
University of Guelph

Clarireedia jacksonii is a destructive foliar pathogen that causes dollar spot disease on closely mown
turfgrass around the world. The common method of managing dollar spot involves applying fungicides
throughout the growing season, usually at 2-3 week intervals, but there are increasing societal concerns
about pesticide use. Ferrous sulfate has been mentioned as a possible alternative to commercial
fungicides, but its effects on different turfgrass cultivars and this fungus is not known. In this study,
2
ferrous sulfate heptahydrate (FSH) was applied weekly at low 1x (250 g/100m ) and high 5x (1250
2
g/100m ) rates, and was compared to the commercial fungicide Banner Maxx on up to 10 cultivars of
creeping bentgrass. Significant differences in the response of different cultivars to the low FSH rate were
found (ranging from 47.5% to 85.9% disease suppression), and the high rate had similar disease
suppression levels as the fungicide. However, darkening was evident, which led to discolouration trials at
1x to 15x rates. Increasing rates of FSH intensified darkening, which significantly decreased by two
weeks later and almost completely dissipated by four week later. FSH also showed direct toxicity to
fungal growth, but only significantly at higher rates. It did not significantly reduce grass height and
biomass growth at low rates. FSH should be developed as a viable commercial control of dollar spot and
other turfgrass diseases.

Matthew Rudland (mrudland@uoguelph.ca)

S42. In vitro and in-field response of Stemphylium vesicarium to foliar fungicides
2
3
*1
S. Stricker ; Pethybridge, S.J. ; B. Gossen ; M.R. McDonald
1
1 University of Guelph
2 Cornell University
3 Agriculture and Agri-Food Canada
Stemphylium leaf blight (SLB) of onion, caused by Stemphylium vesicarium (Wallr.) E.G. Simmons, can
cause severe leaf necrosis resulting in small, unmarketable bulbs. To manage SLB, growers typically
apply fungicides on calendar-based schedules that do not depend on weather conditions or pathogen
biology. This can result in more applications than necessary, which increases the risk of fungicide
insensitivity. Isolates of S. vesicarium were collected from onion and leek in southern Ontario to
assesssensitivity to azoxystrobin (a strobilurin fungicide) and pyrimethanil (an anilinopyrimidine
fungicide) comparedagainst an unexposed baseline isolate collected in 1995. The baseline isolate was
-1
-1
sensitive to azoxystrobin at 0.5 µg ml plus 100 µg ml salicylhydroxamic acid (SHAM) and to
pyrimethanil at 5.0 µg ml , assessed as decreased mycelial growth and conidia germination on amended
-1
media. Of 10 isolates collected in 2018, 9 isolates exhibited decreased sensitivity to azoxystrobin and 7
isolates had decreased sensitivity to pyrimethanil. There were no differences in fitness (growth or
sporulation) between insensitive and sensitive isolates. A field trial using a weekly foliar spray program
of Quadris Top (difenoconazole and azoxystrobin) alternated with Luna Tranquility (fluopyram and
pyrimethanil) reduced SLB symptoms by only 10%. This demonstrates that these fungicides no longer
provide effective reduction of SLB on onion in southern Ontario, even with repeated application, due at
least in part to fungicide insensitivity.

Sara Stricker (strickes@uoguelph.ca)

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