Mefenoxam Insensitivity of P. capsici Isolates Collected in South Carolina in 2003
County (Farm) Crop Sensitive Intermediately
sensitive Insensitive Total Lexington (1) Bell pepper 0 10 0 10 Lexington (1) Summer squash 0 7 5 12 Bamberg Summer squash 19 0 0 19 Bamberg Zucchini 17 0 0 17 Lexington (2) Bell pepper 19 29 2 50 Lexington (2) Jalapeno pepper 5 6 1 12 Total 60 52 8 120
Keinath, A.P. 2007. Plant Disease 91:743-748.
General Procedures
4 aliquots of zoospore suspensions counted
1 to 4, varied by assaySubsamples
Mostly linear with log (mg/L)Regression
2 platesReplications
2 to 3Tests
0, 0.03, 0.10, 0.31 [1.0]
3-4 concentrations plus 0;Evenly spaced on log scale at 1 or 0.5 log units apart
Fungicide Concentration (mg/L)
ExampleLevelsFactor
Reference: Keinath, A.P. 2007. Plant Disease 91:743-748.
Sandwich Plate Technique for Producing Zoospores
in the Presence of a Fungicide that Reduces Sporangium Formation
Young and Vjugina, 2002. Phytopathology 92:S89.
V8 agar
Water agar + Fungicide
Chilled SDW
Calculating EC50 Values with Regression Equations
Log zoxamide concentration-1.5 -1.0 -0.5 0.0 0.5
Rel
ativ
e zo
ospo
re c
ount
(%)
0.0
0.2
0.4
0.6
0.8
1.0
Test 1 Test 2 Test 3 Predicted
Isolate RCS4
1.800.255-0.5770.6474LP48
0.21-0.682-0.3150.2845RCS4
EC50log10 EC50
SlopeInter-cept
Isolate
EC50 Values for Zoospore Cyst Germination on Dimethomorph-Amended V8 Agar
0.00
0.02
0.04
0.06
0.08
0.10
0.12
Dim
etho
mor
ph E
C50
(mg/
L)
Isolate of Phytophthora capsici
Lexington 1 Lexington 2Bamberg
0.00
0.02
0.04
0.06
0.08
0.10
0.12
Dim
etho
mor
ph E
C50
(mg/
L)
Isolate of Phytophthora capsici
Lexington 1 Lexington 2Bamberg
Mean, Median = 0.07 mg/L
Keinath, A.P. 2007. Plant Disease 91:743-748
EC50 Values for Zoospore Production on Zoxamide-Amended Agar
Isolate of Phytophthora capsici
Zoxa
mid
e EC
50 (m
g/L)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Lexington 1 Lexington 2Bamberg
Isolate of Phytophthora capsici
Zoxa
mid
e EC
50 (m
g/L)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Lexington 1 Lexington 2Bamberg
Mean = 0.47 mg/LMedian = 0.29 mg/L
Summary of EC50 Values (mg/L)
Fungicide Mycelial Growth
Zoospore Germination
Zoospore Production
Dimethomorph 0.19 ± 0.02
0.18 0.07 ± 0.02
0.07 0.63 ± 0.42
0.53 **
Zoxamide 0.50 ± 0.52 0.33 **
n.a. 0.47 ± 0.51 0.29 **
Cymoxanil > 50 > 50 <50
Mean ± Std Dev.Median, ** indicates Non-normal Distribution
Keinath, A.P. 2007. Plant Disease 91:743-748
0
0.05
0.1
0.15
0.2
0.25
EC50 Values for growth of P. capsici isolates on Fluopicolide amended V8 agar
Mean=0.161 mg/L
Fluo
pico
lide
(mg/
L)
Range=0.098-0.239 mg/L
NC SC GA FL
Fungicide Mycelial growth Sporulation
P.infestansFluopicolide 0.161 0.059 4.1
0.098-0.24 <0.03-0.062
Mandipropamid 0.022 0.0080.008-0.032 <0.0015-0.032 0.02-2.98
EC50 values (mg/L) for P. capsiciagainst new fungicides
Kousik & Keinath, 2007
Mycelial growth of P. capsici isolates on Cyazofamid amended V8 juice agar
Check, 0 mg/L 300 mg/L
0
50
100
150
200
250
300
EC50 Values for growth of P. capsici isolates on Cyazofamid and SHAM amended agar
Cya
zofa
mid
(PPM
)
Range=<1 to >300 mg/L
NC SC GA FL
100 mg/L Salicylhydroxamic acid
Check Ranman Fungicide X
Effect of Ranman (2.75 fl oz/A) on Fruit Rot of Watermelon caused by P. capsici isolates
Ranman concentrations
0 Check10 100300
Growth of P. capsici Isolates on Ranman treated Cucumbers
Silwett L-77 (2 Fl Oz/A)
Cyazofamid (mg/L)
3 P. capsici isolates6 replications
0 10 100 300 mg/L Cyazofamid
Isolate 1
Isolate 2
Isolate 3
EC50
13.7 mg/L(4)
>300 mg/L(108)
233 mg/L(Spore:68)
Fungicide Mode of Action Resistance Risk
Mefenoxam Inhibits RNA synthesis High
Dimethomorph Phospholipid biosynthesis Low-Med& cell wall synthesis
Mandipropamid Phospholipid biosynthesis Low-Med& cell wall synthesis
Zoxamide β tubulin assembly in mitosis Low-Med
Cyazofamid Respiratory inhibitor, QiI Med-High
Fluopicolide disrupts membrane activity Res. not known
FRAC Code List
FRAC: Fungicide resistance action committee www.frac.info/publications