Optimizing management of cercospora leaf spot (Cercospora beticola) of sugarbeet in the wake of fungicide resistance

Figures & data

Table 1. Number of fungicide applications and application dates for fungicide schedules used to manage Cercospora leaf spot of sugar beet at Pain Court (PC) and Ridgetown (RT), Ontario, 2013–2015.

	Fungicide schedule ^a
	BEETcast™ 50/35		BEETcast™ 55/50		Calendar (14-day interval)
	DAFA ^b	No. applications	DAFA	No. applications	DAFA	No. applications
PC
2013	0 (25 Jun) ^c, 14, 30, 55, 69	5	0 (27 Jun), 20, 53, 78	4	0 (27 Jun), 14, 25, 41, 50, 60, 70, 79, 89	9
2014	0 (23 Jun), 22, 44, 64	4	0 (25 Jun), 34, 63	3	0 (25 Jun), 13, 23, 37, 50, 57, 68	7
2015	0 (17 Jun), 21, 41, 58, 76	5	0 (19 Jun), 32, 63	3	0 (19 Jun), 14, 24, 38, 47, 59, 69	7
RT
2013	0 (1 July), 15, 30, 60, 76	5	0 (4 Jul), 21, 55	3	0 (4 Jul), 16, 26, 40, 50, 61, 72	7
2014	0 (27 June), 20, 44, 60, 76	5	0 (2 Jul), 35, 63	3	0 (2 Jul), 13, 23, 37, 47, 57, 68	7
2015	0 (23 June), 22, 38, 58, 77	5	0 (25 Jun), 27, 56, 85	4	0 (25 Jun), 15, 25, 40, 50, 60, 70	7

^a Symptoms were first observed in Pain Court on 12 Aug 2013, 10 Sep 2014 and 23 July 2015 and in Ridgetown on 16 July 2013, 16 July 2014, and 23 July 2015.

^b DAFA = days after first application. Prothioconazole (175.2 g Ha⁻¹) + mancozeb (1687.5 g Ha⁻¹) were applied for the first and third applications, and mancozeb alone for the remaining applications. Applications were made within ± 4 DSVs of the target except for the second and third 55/50 applications in Pain Court 2015 (56 and 60 DSVs), the fourth 50/35 application in Ridgetown 2015 (44 DSV), the third 55/50 application in Ridgetown 2015 (62 DSV), and the third 55/50 application in Ridgetown 2014 (56 DSV).

^c First application date.

Fig. 1 Weekly progression of mean Cercospora leaf spot severity on sugar beet in Pain Court and Ridgetown, Ontario, in 2013, 2014 and 2015 comparing several fungicide spray schedules using a carrier volume of 235 L ha⁻¹. Data were log10 transformed with back transformed means presented, confidence intervals are presented in Table S1. Data points in individual figures with the same letter were not significantly different on the final assessment date at P ≤ 0.05 Tukey’s adjustment. For figures with an ‘*’, differences are discussed in the text. Confidence intervals (95%) are available in Table S1.

Table 2. Standardized area under disease progress curve (sAUDPC) (per day) for Cercospora leaf spot in sugar beets treated with different fungicide spray schedules and carrier volumes, Pain Court (PC) and Ridgetown (RT), Ontario, 2013–2015.

		sAUDPC (95% CI) ^a
Schedule ^a	Carrier volume (L ha^−1)	PC & RT 2013	PC 2014, RT 2014, & PC 2015	RT 2015
Control	none	1.29 a (0.78, 1.95)	11.0 a (6.21, 18.81)	39.66 a (3.51, 4.55)
Calendar	115	0.61 ab (0.25, 1.08)	0.78 d (0.24, 1.53)	4.54 d (0.75, 1.53)
Calendar	235	0.64 ab (0.27, 1.11)	0.96 cd (0.44, 1.67)	2.33 d (0.31, 1.16)
BEETcast™ 50/35	115	0.32 b (0.02, 0.70)	2.21 bcd (0.90, 4.43)	20.00 bc (2.31, 3.25)
BEETcast™ 50/35	235	0.85 ab (0.43, 1.38)	2.22 bcd (1.22, 3.68)	13.40 c (1.47, 3.11)
BEETcast™ 55/50	115	0.87 ab (0.45, 1.41)	3.44 b (1.37, 7.31)	25.97 ab (2.70, 3.72)
BEETcast™ 55/50	235	0.68 ab (0.31, 1.17)	2.47 bc (1.02, 4.97)	25.66 ab (2.53, 3.90)
P-value		0.1219	<.0001	<.0001
Contrast	115	0.58 a (0.36, 0.83)	1.93 a (1.18, 2.95)	13.63 a (1.61, 2.95)
	235	0.72 a (0.40, 1.12)	1.80 a (1.21, 2.54)	9.85 b (1.16, 2.67)
P-value		0.4162	0.7093	0.0090

^a Numbers in a column followed by the same letter are not significantly different at P ≤ 0.05 Tukey’s adjustment. Data were pooled due to lack of a site × treatment interaction. Data underwent a log10 transformation to meet assumptions of normality and the back transformed means are presented. One outlier was removed from the BEETcast™ 50/35 115 L ha⁻¹ treatment in the second replication in Pain Court 2014.

Table 3. Root and sucrose yield from sugar beets harvested from plots treated with different spray schedules and carrier volumes for management of Cercospora leaf spot, Pain Court (PC) and Ridgetown (RT), Ontario, 2013–2015.

Schedule ^a	Carrier volume (L ha^−1)	Total Yield (T ha^−1)	RWSH ^b (kg ha^−1)	RWS ^c (kg T^−1)	Sucrose (%)	CJP ^d (%)
Control	none	83.9 a ^e	9848 b	122.5 b	16.7 b	94.8 a
Calendar	115	87.3 a	11 021 a	133.6 a	17.9 a	95.5 a
Calendar	235	89.4 a	11 044 a	131.3 a	17.7 a	95.3 a
BEETcast™ 50/35	115	87.8 a	10 477 ab	131.4 a	17.7 a	95.1 a
BEETcast™ 50/35	235	84.0 a	10 146 ab	133.0 a	17.9 a	95.3 a
BEETcast™ 55/50	115	90.9 a	10 824 ab	128.4 ab	17.4 a	95.1 a
BEETcast™ 55/50	235	85.8 a	10 779 ab	130.7 a	17.6 a	95.2 a
S.E. ^f		2.3	256	1.5	0.2	0.2
P-value		0.0656	0.0079	<.0001	<.0001	0.0520
Contrast	115	88.7 a	10 774 a	131.1 a	17.7 a	95.2 a
	235	86.4 a	10 656 a	131.7 a	17.7 a	95.3 a
S.E.		1.6	209	1.1	0.2	0.1
P-value		0.1286	0.5746	0.6489	0.7026	0.6005

^a All data, with the exception of total root yield, were unavailable for Ridgetown 2013 control treatment in the first replication.

^b RWSH = Recoverable white sucrose per hectare.

^c RWS = Recoverable white sucrose per tonne.

^d CJP = Clear juice purity.

^e Numbers in a column followed by the same letter were not significantly different at P ≤ 0.05 Tukey’s adjustment. Data were pooled over sites due to lack of a site × treatment interaction.

^f Standard error of control was different than other treatments for RWSH (263).

Table 4. Cost analysis of different spray schedules from plots treated with different fungicide application timings and carrier volumes for management of Cercospora leaf spot, Pain Court and Ridgetown, Ontario, 2013–2015.

Programme ^a	Application Carrier Volume (L ha^−1)	Profit Margin ^b ($)
Control		4339 a ^c
Calendar	115	4261 a
Calendar	235	4110 a
BEETcast™ 50/35	115	4232 a
BEETcast™ 50/35	235	4040 a
BEETcast™ 55/50	115	4384 a
BEETcast™ 55/50	235	4334 a
S.E. ^d		120
P-value		0.7731
Contrast	115	4292 a
	235	4161 a
S.E.		94
P-value		0.7010

^a Pain Court 2013 control treatment in the first replication was removed from analysis because the data were unavailable.

^b Profit margin = gross payment – (application cost + fungicide cost + trucking cost); where payment = $ ha⁻¹, mancozeb cost = $ 17.00 ha⁻¹ × number of applications, prothioconazole cost = $63.00 ha⁻¹ × number of applications, application cost with 115 L ha⁻¹ = $22.00 ha⁻¹ × number of fungicide applications, application cost with 235 L ha⁻¹ = $30.00 ha⁻¹ × number of fungicide applications and trucking cost (ha⁻¹) = (sucrose yield ton ac⁻¹ × $6/ton)/0.405. Costs and revenues were calculated assuming parity between USD and CAD for simplicity.

^c Numbers in a column followed by the same letter were not significantly different at P ≤ 0.05 Tukey’s adjustment, data pooled over sites due to lack of a site × treatment interaction.

^d Standard error of control was 124.