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