Fungicide Control of Cercospora Leaf Spot (CLS)

Larry J. Smith, Head; Todd Cymbaluk and Jeffrey Nielsen, Assistant Scientists;

University of Minnesota, Northwest Research and Outreach Center

Crookston, MN 56716

There were 45 treatments in the 2005 trial (Table 2). Treatments that are blank for fungicide type and rate represent treatments that do not follow resistance management practices. The data is shown for reference purposes only. Information relative to cultural and fungicide practices is shown in Table 1.

Results and Discussion:

Cercospora Leaf Spot (CLS) Development

The border rows (1 and 6) were inoculated with ground sugarbeet leaves containing CLS on July 8, 2005. CLS developed on these plants approximately two weeks after inoculation. Initial fungicide application began on July 27, unless otherwise shown in Table 1.Weather conditions were excellent for buildup and spread early, tapered off for the first three weeks of August due to dryness, and then resumed development the last weeks in August throughout September. Significant rainfall (4.5 inches) occurred on August 17-19 and again on September 5 (1.5 inches), which coupled with ideal temperatures caused rapid spread and development. The level of disease in this trial was severe (KWS 7.32) compared to commercial fields in the area. This was due to low inoculum levels in the commercial fields verus this trial being inoculated to produce CLS.

Treatment Observations

All fungicide treatments significantly increased RSA and yield compared to the control (Table 1). Applications that favored CLS control into September (September 7 application) out performed those treatments where the last application was applied on August 23. There were 21 treatments in the trial where four applications of fungicide were applied compared to 21 treatments receiving only three applications. The four application programs had an average RSA and gross return of 8216 lbs and $957, compared to 7865 lbs and $904 for the three application programs. Taking only the top 10 treatments in each category, the difference in RSA and gross return increases (8535 lb RSA and $998 vs 8089 lb RSA and $940).

Delaying the first application or stretching the time between the first and second fungicide application or the second and third application (21 days) beyond that recommended by the manufacturer reduced RSA and yield. This is clearly evident in the Eminent/Headline and Headline/Eminent treatments where the first fungicide application was delayed 14 days and the application interval was stretched to 21 days between the first application and second application.

There were two experiment triazole compounds in the trial. Flutriafol applied four times at a 14-day interval performed equal to Eminent in the same program. Flusilazole applied four times had significantly higher RSA than either Eminent or Flutriafol. Flusilazole and Eminent both had EC-50 for tetraconazole > than 1.0 however.

The triphenyltin hydroxide (TPTH) performed poorly compared to 2004. The level of tolerance (resistance) was more apparent late in the season and in treatments where TPTH was the last application in either a three or four application program.

The visual vigor ratings are highly correlated to RSA obtained. The correlations, however, is not as strong as observed in previous years.

Table 1.	Cultural practices, fungicide application dates and harvest date of Cercospora Leaf Spot trial at Crookston, 2005

Soil Test:	0-2 foot 25 lb nitrogen	1-6 inch 11 ppm phosphorus

2-4 foot 4 lb nitrogen	1-6 inch 144 ppm potassium

Fertilized	110 lb N per Acre

70 lb P2O5 per Acre

Planted	April 25, 2005

(Seed spacing 1.5 inches, 22 inch row spacing, plot 6 row x 35 feet)

Variety	Croplan CL101 (KWS 5.18)

Insecticide	Counter 1.8 lb ai/A

Thinned	May 30, 2005	(35,600 plants/A)

Herbicide	May 31, 2005	June 6, 2005	June 28, 2005	July 6, 2005

"micro-rate"	"micro-rate"	1.5 pt Betamix	13 oz Select

Betamix	Betamix	½ oz UpBeet

UpBeet	UpBeet

Stinger	Stinger

Select	Select

MSO	MSO

Herbicide	13 gallons per acre	TeeJet 8003 flat fan nozzles

Application	Tractor mounted sprayer	30 psi

Fungicide	14 Day	14 21 Day	21 14 Day	21 Day

July 27, 2005	July 27, 2005	July 27, 2005	July 27, 2005

August 9, 2005	August 9, 2005	August 16, 2005	August 16, 2005

August 23, 2005	August 30, 2005	August 30, 2005	September 7, 2005

September 7, 2005

Fungicide	19.0 gallons per acre	TeeJet 11002 flat fan nozzles

Application	Tractor mounted sprayer	100 psi

Cultivated	June 2, 2005

June 20, 2005

Harvested	October 11, 2005

Other	Ground infected cercospora leaves surface applied on canopy of border rows,

innoculated July 8, 2005

Table 2.	Cercospora leaf spot control with registered and experimental fungicides - 2005

Not for publication or distribution without the consent of Dr. Larry J. Smith, University of Minnesota, Northwest Research & Outreach Center, Crookston, Minnesota

Trt & Rate Product (lb, oz or ai/A)

Appl

#

Appl. Interval *

RSA RST (lb/A) (lb/T)

Root Yield (T/A)

Sugar (%)

LTM

(%)

CLS*

Vigor**

(1-10)

Gross Return

($/A) ***
4	14	8783	323.5	27.2	17.13	0.95	1.50	7.50	1041
Gem/Topsin+TPTH/TPTH & Dithane/Headline 3.37 oz/7.6 oz+3.75 oz/3.75 oz + 2 lb/9 oz

4

14

8662

321.0

27.0

17.00

0.95

2.50

6.75

1019
Headline/9oz/Eminent/13 oz/TPTH 5 oz/ Headline 9 oz

4

14

8655

321.0

27.0

17.08

1.03

2.50

6.63

1017
4	14	8633	320.5	26.9	17.10	1.08	2.38	6.75	1015
Fluisazole 7 oz/TPTH 5 oz/Headline 9 oz/ TPTH 5 oz

4

14

8602

317.0

27.2

16.93

1.08

2.50

6.50

999
3	21	8551	324.0	26.4	17.20	1.00	2.38	7.13	1016
TPTH 5 oz/Eminent 13 oz/Headline 9 oz/ TPTH 5 oz

4

14

8438

317.5

26.6

16.85

0.98

3.13

6.50

982
Topsin + TPTH 7.6 oz + 5 oz/Eminent 13 oz/ TPTH 3.75 oz/ Gem 3.37 oz

4

14

8418

312.0

27.0

16.63

1.03

3.38

6.13

962
Eminent 13 oz/TPTH 5 oz/Headline 9 oz/ TPTH 5 oz

4

14

8400

324.0

25.9

17.20

1.00

3.75

6.00

997
Eminent 13 oz/TPTH 5 oz/ Headline 9 oz	3	21/14	8320	320.5	26.0	17.03	1.00	4.00	6.26	977
TPTH 5 oz/Eminent 13 oz/Headline 9 oz	3	14/21	8222	322.0	25.5	17.18	1.08	3.50	6.50	971
TPTH 5 oz/Eminent 13 oz/Headline 9 oz	3	14	8222	319.5	25.7	16.98	1.00	3.50	6.25	963
Eminent 13 oz/Topsin+TPTH 7.6 oz +3.75 oz/Gem & Dithane 3.37 +2.0 lb

3

14

8215

325.0

25.3

17.15

0.90

3.25

6.38

978
Eminent 13 oz/Topsin +TPTH 7.6 oz + 3.75 oz/Gem 3.37 oz / TPTH 3.75 oz

4

14

8212

312.5

26.3

16.70

1.08

3.00

6.50

941
4	14	8206	315.5	26.0	16.80	1.03	3.38	6.38	949
Enable 8 oz/Headline 9 oz/Enable 8 oz/Headline 9 oz

4

14

8178

311.5

26.3

16.68

1.10

2.25

6.75

933
3	21	8126	317.0	25.6	16.88	1.03	4.38	5.63	944
Headline 9 oz/Eminent 13 oz/TPTH 5oz	3	14	8118	318.5	25.5	16.93	1.00	4.00	6.00	948
Eminent 13 oz/TPTH 5 oz/Headline 9 oz	3	14	8068	311.0	25.9	16.60	1.05	3.88	6.38	919
Eminent 13 oz/TPTH 5 oz/Headline 9 oz

(Appl 2,3,4)

3

14

8062

312.5

25.8

16.63

1.00

4.00

5.88

922
4	14	8058	321.0	25.1	17.13	1.08	3.38	6.00	948

4

14

8015

314.0

25.5

16.78

1.08

2.00

6.13

922
TPTH 5 oz/Headline 9 oz/Eminent 13 oz/TPTH 5 oz

4

14

7949

312.0

25.5

16.67

1.08

3.25

6.50

908

Trt & Rate Product (lb, oz or ai/A)

Appl

#

Appl. Interval *

RSA RST (lb/A) (lb/T)

Root Yield (T/A)

Sugar (%)

LTM

(%)

CLS*

Vigor**

(1-10)

Gross Return

($/A) ***
Eminent 13 oz/Topsin + TPTH 10 oz + 5 oz/Headline 9 oz

3

21/14

7915

311.5

25.4

16.63

1.05

3.88

6.13

903
Eminent 13 oz/Topsin + TPTH 7.6 oz + 3.75 oz/ Gem 3.37 oz

3

14

7888

311.5

25.4

16.58

1.00

3.63

6.00

898
Enable2F 8 oz/Topsin+TPTH 7.6oz + 3.75 oz/Enable 8 oz/TPTH 5 oz

3

14

7853

3200

24.6

17.00

1.00

3.75

5.88

921
Gem 3.37 oz/TPTH 5 oz/Eminent 13 oz	3	14	7848	320.0	24.6	17.00	1.00	4.00	5.88	920
Headline 9 oz/TPTH 5 oz/Eminent 13 oz

(Appl 2,3,4)

3

14

7846

309.5

25.4

16.60

1.13

3.75

5.75

888
4	14	7830	321.0	24.4	16.98	0.93	4.00	6.00	921
Gem 3.37 oz/Topsin + TPTH 7.6 oz +3.75 oz/TPTH + Dithane 3.75 oz + 2.0 lb

3

14

7814

310.0

25.2

16.50

1.00

4.38

5.88

887
4	14	7796	313.0	24.9	16.68	1.03	3.75	5.75	894
Headline 9 oz/TPTH 5 oz/Eminent 13 oz	3	21/14	7767	317.5	24.5	16.88	1.00	4.13	5.88	904
Eminent 13 oz/Topsin + TPTH 7.6 oz + 5 oz/ Headline 9 oz

3

21/14

7747

311.0

24.9

16.60

1.05

3.75

5.40

882
Headline 9 oz/TPTH 5 oz/Eminent 13 oz	3	14	7740	317.0	24.4	16.85	1.00	3.88	6.25	899
Eminent 13 oz/Headline 9 oz/TPTH 5 oz	3	14	7659	312.5	24.5	16.8	1.05	3.88	5.75	877
Eminent 13 oz/TPTH 5 oz/Gem 3.37 oz	3	14	7647	311.5	24.6	16.68	1.10	4.00	5.75	872
Eminent 13 oz/Headline 9 oz/Eminent 13 oz	3	14	7607	307.5	24.8	16.48	1.10	4.13	5.75	855
4	14	7593	318.0	23.9	16.95	1.05	4.75	5.38	884
4	14	7576	318.0	23.8	16.95	1.05	3.38	5.75	883
TPTH 5 oz/ Headline 9 oz / Eminent 13 oz	3	14	7563	312.0	24.2	16.60	1.00	4.00	5.75	865
Eminent 13 oz / Topsin + TPTH 7.6 oz + 3.75 oz /Gem 3.37 oz

3

21/14

7540

307.0

24.6

16.38

1.03

4.13

5.75

847
Eminent 13 oz/ Headline 9 oz/TPTH 5 oz	3	21/14	7353	305.5	24.1	16.38	1.10	4.50	5.13	822
Eminent 13 oz/ Headline 9 oz (app 2,3)	2	21	7340	310.0	23.7	16.63	1.13	5.13	5.25	832
Headline 9 oz/ Eminent 13 oz (appl 2,3)	2	21	7105	305.0	23.3	16.40	1.15	4.75	4.75	792
Check	0	--	5663	299.5	18.9	16.10	1.13	7.38	1.38	618
LSD05	576	15.9	1.4	0.72	0.14	0.58	0.54
* CLS measured on KWS scale (1 = no leaf spot, 9 = dead outer leaves and regrowth of new leaves)

** Vigor = Visual vigor rating at harvest ( 1= poor, 10 = excellent)

*** Basis - ACSC November 15, 2005 payment