Page 129 - PC2019 Program & Proceedings

PLANT CANADA 2019

S43. Evaluation of yield losses and pyraclostrobin sensitivity in Leptosphaeria maculans, cause of
blackleg of canola
*
Wang, Y. ; S-F. Hwang; A. Akhavan; S. Strelkov
University of Alberta

Blackleg (Brassica napus L.), caused by Leptosphaeria maculans (Desm.) Ces. & de Not., is an
important disease of canola worldwide. In Canada, blackleg is managed mainly by the cultivation of
resistant or moderately resistant canola hybrids and the application of fungicides. Field experiments were
conducted in central Alberta in 2017 and 2018 to determine the relationship between blackleg severity
and yield in two moderately resistant hybrids ‘73-15RR’ and ‘1950RR’. Seed yield per plant was found to
decrease as a consequence of L. maculans infection, with regression analysis showing that the relationship
between yield and disease severity was best explained by second degree quadratic equations. Sensitivity
to the fungicide pyraclostrobin, a strobilurin that is commonly applied as a foliar and seed treatment for
blackleg and other diseases, was compared in L. maculans collections made in Alberta in 2011 and 2016.
The half-maximal effective concentration (EC50) of pyraclostrobin was determined using agar and
microtiter plate assays, and two discriminatory doses of the fungicide were selected to identify highly
insensitive isolates in the collections. The mean EC50 was approximately 4× greater for the isolates
collected in 2016 versus those collected in 2011. While almost all isolates were still sensitive to
pyraclostrobin, this increase in the EC50 suggests that proper fungicide stewardship is warranted for the
sustainable long-term management of L. maculans.

Yixiao Wang (yixiao2@ualberta.ca)

S44. Effects of solarization, anaerobic soil disinfestation and mustard biofumigation on ginseng
replant disease
*1
Shi, A. ; S. Westerveld 2
1 University of Guelph
2 Ontario Ministry of Agriculture, Food and Rural Affairs

Ginseng replant disease (GRD) threatens the survival of the industry. Because of GRD, ginseng cannot be
grown on the same land twice without considerable crop losses. To assess the effects of various soil
treatments on GRD, a research trial was established in Ontario in 2016. The site was seeded eight years
after harvest of a previous ginseng crop. The trial was arranged in a split-plot design with fumigant
(metam-sodium) as the main-plot and treatment as the sub-plot with four replications. The treatments
included solarization (tarped control), anaerobic soil disinfestation (ASD) (orchard grass), ASD
(molasses), ASD (orchard grass + molasses), mustard seed meal (Brassica juncea + Sinapis alba) (6.7
ton/ha), mustard seed meal (3.35 ton/ha), mustard cover crop (B. juncea + S. alba) and untarped control.
Plant stands were recorded during the growing season of 2017 and 2018 and roots were assessed each fall.
Untarped control plots were nearly destroyed by GRD by 2018. Fumigated plots had much higher yield
than unfumigated plots. When analyzing fumigated and unfumigated treatments together, mustard cover
crop had the highest total and marketable yield. Solarization and ASD treatments also reduced disease
compared to the control. The results suggest that fumigation does provide some control of GRD, but
control is improved with mustard biofumigation, ASD and solarization. This trial will be monitored in
2019 to determine treatment efficacy at final harvest.

Amy Fang Shi (fshi@uoguelph.ca)

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