Early fungicide treatment reduces blackleg on canola but yield benefit is realized only on susceptible cultivars under high disease pressure

Figures & data

Fig. 1 A pictorial key (scale 0–5) for the assessment of blackleg severity based on % area of blackened stem tissue on the cross section cut through the crown of plant. A score of ‘0’ indicates the absence of disease and ‘5’ shows 100% disease with stem constrictions (dry and dead). The increment between ‘0’ and ‘4’ is 25%. At ‘4’, the blackened tissue may exceed 75%, but there is generally no constriction of the stem and the plant is not completely dead

Table 1. Fungicides registered for foliar treatment against blackleg of canola in Canada as of 2011 and used in this study

Product	Common name	Concentration (a.i.) ^#	Mode of action ^ζ	Label rate (/ha)	Registrant
Headline® EC	pyraclostrobin	250 g/L	QoI	350 mL	BASF Canada
Quadris® F	azoxystrobin	22.9%	QoI	512 mL	Syngenta Canada
Tilt®250 E	propiconazole	250 g/L	DMI	500 mL	Syngenta Canada
Quilt®	azoxystrobin + propiconazole ^ξ	75 g + 125 g/L	QoI + DMI	1000 mL	Syngenta Canada

^#The amount of active ingredient based on product label.

^ζQoI: Quinone outside inhibitors (Group 1), and DMI: De-methylation inhibitors (Group 3).

^ξThe two active ingredients are pre-mixed in the product formulation.

Table 2. Effect of fungicide treatment and application timing on mean disease incidence (MDI) and disease severity index (DSI) of blackleg on Westar in western Canada (13 station years)

Fungicide treatment	Spray timing	MDI (%) ^ζ	DSI (%) ^ζ
Control (unsprayed)	NA	67.9 A	31.8 B
Pyraclostrobin	2–4 leaf	52.2 CD	26.2 C
Azoxystrobin	2–4 leaf	51.8 CD	21.5 D
Propiconazole	2–4 leaf	69.2 A	37.8 A
Azoxystrobin + propiconazole ^δ	2–4 leaf	57.0 BC	23.9 D
Pyraclostrobin	Bolting	61.0 B	31.4 B
Propiconazole and pyraclostrobin ^#	2–4 leaf, bolting	55.4 C	26.9 C
Pyraclostrobin and propiconazole ^#	2–4 leaf, bolting	48.7 D	22.6 D

^δThe two active ingredients are pre-mixed in the product formulation.

^#Two applications; the 1^st product was applied at 2–4 leaf stage, and 2^nd product at early bolting.

^ζMeans with the same letter(s) do not differ (LSD, P ≤ 0.05). SE = 6.2 and 4.3, respectively, for MDI and DSI mean comparisons.

Table 3. The effect of fungicide treatment and application timing on seed yield of the blackleg susceptible cultivar Westar in western Canada (12 station years). ^δ.

Fungicide treatment	Spray timing	Yield (kg/ha) ^ξ
Control (unsprayed)	NA	1441.4 C
Pyraclostrobin	2–4 leaf	1829.0 A
Azoxystrobin	2–4 leaf	1766.0 A
Propiconazole	2–4 leaf	1500.6 BC
Azoxystrobin + propiconazole ^#	2–4 leaf	1678.7 AB
Pyraclostrobin	Bolting	1496.7 BC
Propiconazole and pyraclostrobin ^ζ	2–4 leaf, bolting	1720.2 A
Pyraclostrobin and propiconazole ^ζ	2–4 leaf, bolting	1820.3 A

^δDI and DSI were 28–96% and 8–69%, respectively, in these station years. The yield data from the 2014 Brandon trial was not included due to exceptionally depressed yield (< 10% of average) caused by extremely poor emergence, couple with a severe drought later in the growing season.

^#Pre-mixed in the product formulation.

^ζThe 1^st product was applied at 2–4 leaf stage, and 2^nd product at early bolting, respectively.

^ξMeans with the same letter(s) do not differ (LSD, P ≤ 0.05). SE = 162.7.

Table 4. Effect of pyraclostrobin treatment at the 2–4 leaf stage on mean disease incidence (MDI) and disease severity index (DSI) of blackleg (13 station years), and yield (12 station years) on the blackleg resistant varieties 43E01 (MR) and 45H29 (R)

Variety	Treatment	MDI (%) ^δ	DSI (%) ^δ	Yield (kg/ha) ^δ
43E01	Control (untreated)	65.0 A	32.9 A	2,241.1 B
	Pyraclostrobin	48.6 B	19.0 BC	2,194.0 B
45H29	Control (untreated)	53.9 B	21.2 B	2,950.0 A
	Pyraclostrobin	42.3 C	13.7 C	2,926.0 A

^δMeans with the same letter(s) do not differ (LSD, P ≤ 0.05). SE = 7.0 (MDI), 5.0 (DSI) and 272.8 (yield), respectively.

Fig. 2 Regression and correlation of mean disease severity (MDS) to mean disease incidence (MDI) on susceptible (S), moderately resistant (MR) and resistant (R) canola cultivars against blackleg in 17 station-year field trials on the Canadian prairies (2011–2014)