Our results are used for fungicide recommendations by our industry

Gary G S Secor NDSU Melvin Bolton, Bolton ARS, ARS USDA Mohamed Khan, NDSU Viviana Rivera,, NDSU  We have been monitoring g sensitivity y to C. bet...
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Gary G S Secor NDSU Melvin Bolton, Bolton ARS, ARS USDA Mohamed Khan, NDSU Viviana Rivera,, NDSU

 We have been monitoring g sensitivity y to C. beticola in the RRV production area to multiple fungicides the past decade to optimize disease control  We W published bli h d a summary off our work k in i aF Feature t Article in the November issue of Plant Disease entitled “Monitoring fungicide sensitivity of Cercospora beticola of sugar beet for disease management decisions”  If anyone if interested in receiving a copy of this article please let me know in person or e-mail: e mail: [email protected]  Our results are used for fungicide g recommendations by y our industry

Sensitivity to triphenyltin hydroxide of C. beticola isolates collected in ND and MN from 1998-2008 at 1.0 µg/ml as measured by bulk spore germination of 100 isolates/field The blue line shows the decline in the number of triphenyltin isolates/field. hydroxide applications during this period. The arrows show the year of first use of tetraconazole in sugar beet in 1999, trifloxystrobin in 2002 and pyraclostrobin in 2003

80.0

2.5

% Isolates geminated

70.0

2.14

# triphenyltin hydroxide application

Tetraconazole first used

64.6

2

Percent germinate ed isolates

54.3 50.0

1.54

40.0

1.5

1.22

Trifloxystrobin first used

1 30.0

0.88

20.0

Pyraclostrobin 0.86 first used

08 0.8

17.7

0.56

14.9

0.5

0.46

0.45

0.32

9.0

10.0

0 25 0.25

5.1

3.3 1.1

0.97

0.0

2004

2005

2006

0.0

0.0

0 1998

1999

2000

2001

2002

2003

2007

2008

# triphenyltin hydroxid de applications

60 0 60.0

Average EC50 value of Cercospora beticola isolates collected from 1997-2008 to tetraconazole. There is a significant increase in the resistance factor as measured d by b the th average EC50 values l from f 2000-2008 2000 2008 compared d to t the th baseline EC50 values from 1997-1999 (p=0.05) 0.29

0 30 0.30

0.24

0.25

Ave erage EC50 (µg/ml ttetraconazole)

0.23 0.21

0.21

0.21

0.20

0.14

0.15 0.13 0.12

0.12 0.09

0.10

0.05

0.00 1997

1998

1999

2000

2002

2003 Year

2004

2005

2006

2007

2008

Average EC50 values to trifloxystrobin and pyraclostrobin of C. beticola isolates collected in MN and ND from 2003 2003-2008 2008. Note the circled baseline values of isolates collected prior to the use of either fungicide. 0 070 0.070

Pyraclostrobin Trifloxystrobin 0.061

0.060 0.060

Average EC50 (µg/ml)

0.050

0.046

0.039 0.040 0.033 0.030

0.027

0.025

0.023

0.020

0.016 0.012

0.010

0.005 0 003 0.003

0.000 Baseline

2003

2004

2005 Year

2006

2007

2008

Cercospora beticola fungicide sensitivity map illustrating the range of sensitivity to tetraconazole by township in the sugar b t production beet d ti area off ND and MN. Note the clustering (circled) of isolates having high EC50 values (0.1 – 1.0 µg/ml).

Sensitivity of C. beticola field isolates to fungicides in 2009 and 2010 2009

2010

2

1.4

Tetraconazole EC50 average % Isolates > 1ppm

0.250 6.6

0.256 (0.402)* 19

Inspire EC50 average pp % Isolates > 1ppm

0.096 0.5

0.174 (0.243) 8.4

0.022 0

0.111 (0.132) 2.3

Super Tin % germinated isolates (Res)

Headline EC50 average % Isolates > 1ppm • •

* 1st # = without isolates > 1 2nd # () = with isolates > 1

I Impact t off resistance i t • What to all these EC50 values mean to the grower? Do the increased EC50 values mean less disease control? • In order to answer these questions we conducted two studies: di • Field study at Foxhome with two sources of inoculum • Greenhouse study

Field Study y CLS disease September 11, 2010 in identical fungicide trials at Foxhome fungicide trials inoculated with two sources of inoculum

Fungicide Plot Treatment Untreated Super tin Eminent Inspire Headline Proline

CLS Fargo

Crookston

10

10

7.3

6.8

8.3

10

5.8

7.5

6.3

6.3

5.0

8.5

Sensitivity to triazole fungicides of C. beticola isolates collected ll t d from f identical id ti l fungicide f i id trials t i l August A t 30, 30 2010 inoculated with two sources of inoculum at Foxhome Eminent

Fungicide Plot Treatment

Untreated Super tin Eminent Inspire Headline Proline

Inspire

EC50 values

EC50 values

Fargo

Crookston

Fargo

Crookston

0.396

>1

0.065

>1

0.300

0.505

0.060

0.067

0.428

>1

0.092

>1

0.561

>1

0.071

0.878

0.207

>1

0.051

0.766

0.203

>1

0.065

>1

S Source off inoculum i l  5 additional isolates from 6 fungicide plots inoculated with Crookston inoculum ((resistant)) were tested to confirm resistance to triazole fungicides  100% of isolates tested from plots treated with triazole fungicides g were resistant to Eminent;; EC50 >1  26.6% of the isolates were resistant to Inspire; EC50 = 0.647  7% of the isolates were resistant to Headline with EC50 average = 0.163 0 163  Some isolates with EC50 > 1 to all three fungicides  Showed consistent reduced sensitivity to triazole fungicides

Greenhouse Study y  Isolates with three levels of sensitivity to Eminent were used i th in the study t d  Resistant  Intermediate  Sensitive S ii

 Isolates used in this study were chosen for fungicide sensitivity and aggressiveness based on lesion numbers on i inoculated l t d lleaves  Plants treated with 10–fold dilutions of Eminent at concentrations from the field rate of 625 ppm (13 oz/a) to 0 000625 ppm 0.000625  Fungicides were applied using a spray bar to simulate field application  Plants Pl t iinoculated l t d 44-6 6h hours after ft ffungicide i id application li ti

80

40

09-344 07-845 07-558 Headlin ne = 0.480

60

09-260 07-981

20

09-398 09-318 08-640

0 07-230

Hea adline = 0.001

Headline = 0.001

Tetra = 0.008

gh

09-60 09-52

He eadline = 0.297

e

Tetra = 0.30

Tetra = > 1

100 Headlin ne = 0.88

120

Tetra = > 1

140

Headline = > 1

160

Tetra = 0.1

180

Te etra = 0.006

# lesion

IIsolates l t selected l t d ffor GH study t d

220

a

200

ab bc

cd de ef

efg fgh h h

0.0

09-347 Control

 Each treatment consisted of 5 p plants and three replications  Plants were inoculated with a spore suspension of 40,000 spores/ml / l  Plants were incubated in a humid chamber at 37°C under high g light g to allow infection  Plants were transferred to the greenhouse and evaluated for disease after three weeks  Four leaves from each plant were harvested individually and scored for disease  Numbers of lesions  Converted to disease scores

Jones, RK and Windels,C.E. 1991.A management model for Cercospora leaf spot of sugarbeets Minnesota Extension Service AG-FO-5642E.

Sensitivity of C. Beticola to Eminent

Eminent concentration

CLS score

S iti it off C. Sensitivity C beticola b ti l to t H Headline dli

Sensitivity of C. beticola to Headline across all i l isolates ((resistant, i intermediate i di and d susceptible) ibl )

S Summary  Increased resistance to Cercospora p in 2010,, likely y due to higher disease pressure  Some isolates were found to be resistant to Eminent, Inspire and Headline fungicides with EC50 values > 1  Resistant R isolates l affected ff d fungicide f d efficacy ff

 Reduced disease control in field trials with resistant isolates

 Reduced disease control in GH trials showed more disease with isolates with higher EC50 values

 Disease control by Eminent was lost at a concentration of fungicide less than 0.625 ppm  Disease control by Headline was lost at a concentration of fungicide less than 0.127 ppm

 Field and GH data demonstrate a loss of disease control with resistance levels present in the C. beticola population i th in the RRV