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Greg Tylka & Kaitlyn BissonnetteISU Department of
Plant Pathology and Microbiology
Seed Treatments for SCN
Soil Sampling for SCN&
&Decline of SCN Resistance in Iowa
● ~24 days per generation
● 3-6 generations per year
● >200 eggs per female
swollenjuvenile
Tylka
Tylka
female+eggscyst (dead female)full of eggs
Tylka
Tylka
juveniles
Tylka
adultfemale
adult male
Baum
adult female and male –mating occurson root
Tylka
eggs
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Soil Sampling for SCN
l How to sample?
ü 15 to 20 one-inch-diameter soil cores, 6 to 8 inches deep
ü soil cores collected in a zig zag or “M” pattern
ü one 15- to 20-core sample for every 20 acres
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Use a zigzagpattern when collecting soilcores.
OR
Collect soilcores fromlogical areasor “management zones” in
field.
OR
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Collect soilcores fromhigh-risk areas in the field.
l How to sample?l When to sample?
ü spring sampling before soybean cropü fall sampling of soybean
stubbleü fall sampling of nonhost crop
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l How to sample?l When to sample?
ü spring sampling before soybean cropü fall sampling of soybean
stubbleü fall sampling of nonhost cropü during the season
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l How to sample?l When to sample?l Variability of results
Why are SCN soil sample results so variable?
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80 ft
40ft
Curtiss Farm 2000 – Pre Experiment Sampling
Four 10-core soil samples collected in March 2000, one from each
quadrant of the experimental site (1/20 acre each)
X X X
X X X
X X
X X
X X X
X X X
X X
X X
X X X
X X X
X X
X X
X X X
X X X
X X
X X
80 ft
40ft
Curtiss Farm 2000 – Pre Experiment Sampling
Four 10-core soil samples collected in March 2000, one from each
quadrant of the experimental site (1/20 acre each)
0
00
0
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Curtiss Farm 2000 – Initial Population Densities(eggs per 100 cc
soil)
0 0 0 0 0 0 0 50
0 0 0 0 0 0 0 0
0 100 0 0 0 0 0 0
0 50 0 0 0 0 0 50
0 0 0 0 0 0 50 0500 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
10-core soil sample collected from center 12 ft of center 2 rows
of each 4-row x 20-ft plot (64 total, 1/200 acre each) at
planting20 ft
10ft
Curtiss Farm 2000 – Final Population Densities(eggs per 100 cc
soil)
10-core soil sample collected from center 12 ft of center2 rows
of each 4-row x 20-ft plot (64 total, 1/200 acre each) at harvest20
ft
10ft
11,000 5,100 2,900 3,200 350 250 750 2,200
4,100 1,900 1,900 5,900 1,000 2,600 0 100
32,600 19,500 23,700 11,600 8,200 6,400 10,900 3,400
37,000 7,600 9,400 8,400 6,400 6,200 10,700 1,700
16,500 17,600 6,000 1,500 0 3,700 3,700 6,100
19,700 7,600 2,300 50 450 700 250 1,600
12,600 10,600 100 50 0 0 0 50
9,000 4,800 850 0 250 0 0 500
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Why are SCN soil sample results so variable?
egg count = 1,500
egg count = 0
§ List of all avail seed
treatments and MOABrand name Crop(s)Targeted
nematodesActive
ingredientMode
of actioncotton, corn, soybean all ppn
abamectin
inhibits nerve transmission
all all ppn harpin protein bolsters natural
plant defenses
cotton, corn, soybean all ppn Bacillus
firmus
repels nematodes from roots
soybean SCN Pasteuria nishizawae nematode parasite
soybean SCN, RKN fluopyram SDHI enzyme
inhibitor
cotton, corn, soybean
SCN, RKN,reniform, lesion
tioxazafen mitochondrial translation inhibitor
corn, soybean SCN, reniform, lesionBacillus
amylo-‐liquefaciens under investigation
Seed Treatments for SCN
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Clariva§ 9 locations, 3 years
§ 27 site years
§ 12 replicates§ Treatments
§ Cruiser Maxx Advanced + Vibrance
[CM+V]
§ Clariva Complete Beans (Cruiser Maxx
Advanced + Vibrance + Pasteuria nishizawae)
[Clariva]
§ Variety§ 2014 -‐ Asgrow 2433 (MR)§ 2015-‐2016
– NK Soybeans 22-‐S1 (R)
Ilevo§ 9 locations, 2 years
§ 18 site years
§ 12 replicates§ Treatments
§ Poncho/Votivo [PV]§ Poncho/Votivo + Ilevo(fluopyram)
[Ilevo]
§ Variety § Asgrow 2031 (R)
Both § Reproductive Factor (RF)§ Yield
(Bu/Acre)
Materials and Methods
Materials and Methods
SC
WC
NC NE
C EC
NW
SW SE
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Clariva Experiments
Results: Clariva – 2014
“Clariva” RF
“CM+V” RF
“Clariva” RF minus
“CM+V” RFP -‐ value
Northern 2.96 3.35 -‐0.39 0.77
Central1.34 1.91 -‐0.57 0.17
Southern2.48 3.00 -‐0.52 0.56
Combined2.26 2.75 -‐0.49 0.09
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
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Results: Clariva – 2014
“Clariva” Yield
“CM+V” Yield
“Clariva” Yield minus “CM+V”
YieldP -‐ value
Northern 53.7 52.5 1.2 0.58
Central67.2 67.8 -‐0.6 0.76
Southern58.9 58.7 0.2 0.95
Combined59.9 59.7 0.2 0.64
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
Results: Clariva – 2015
“Clariva” RF
“CM+V” RF
“Clariva” RF minus
“CM+V” RFP -‐ value
Northern 1.75 2.22 -‐0.47 0.69
Central1.14 1.44 -‐0.30 0.24
Southern1.66 2.09 -‐0.43 0.54
Combined1.52 1.92 -‐0.40 0.34
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
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Results: Clariva – 2015
“Clariva” Yield
“CM+V” Yield
“Clariva” Yield minus “CM+V”
YieldP -‐ value
Northern 70.7 71.4 -‐0.7 0.76
Central69.0 69.3 -‐0.3 0.85
Southern61.7 62.8 -‐1.1 0.56
Combined67.1 67.8 -‐0.7 0.04
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
Results: Clariva – 2016
“Clariva” RF
“CM+V” RF
“Clariva” RF minus
“CM+V” RFP -‐ value
Northern 9.80 11.44 -‐1.64 0.73
Central5.60 6.73 -‐1.13 0.57
Southern1.23 0.80 0.43 0.20
Combined5.55 6.33 -‐0.78 0.45
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
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Results: Clariva – 2016
“Clariva” Yield
“CM+V” Yield
“Clariva” Yield minus “CM+V”
YieldP -‐ value
Northern 69.1 67.1 2.0 0.55
Central74.0 74.8 -‐0.8 0.61
Southern64.2 63.3 0.9 0.82
Combined69.1 68.4 0.7 0.28
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
Results: Clariva – 2014 – 2016
“Clariva” RF
“CM+V” RF
“Clariva” RF minus
“CM+V” RFP -‐ value
Northern 4.84 5.67 -‐0.83 0.63
Central2.70 3.36 -‐0.66 0.32
Southern1.79 1.97 -‐0.18 0.65
Combined3.11 3.67 -‐0.56 0.37
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
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Results: Clariva – 2014 – 2016
“Clariva” Yield
“CM+V” Yield
“Clariva” Yield minus “CM+V”
YieldP -‐ value
Northern 64.5 63.7 0.8 0.62
Central70.1 70.6 -‐0.5 0.58
Southern61.6 61.6 0.0 0.99
Combined65.4 65.3 0.1 0.92
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
Discussion -‐ Clariva§Reproductive
factor§Variability – individual locations§Only
significant over all locations in
2014
§Yield§No yield effects in 2014 or
2016 § Even at individual locations§
Significant only in SC location over
all 3 years
§No significant yield increases across
environments
§Variable over years and locations§Site
specific
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Ilevo Experiments
Results: Ilevo – 2015
“Ilevo” RF “PV” RF“Ilevo” RF minus
“PV”
RFP -‐ value
Northern 1.26 1.16 0.10 0.66
Central1.44 2.09 -‐0.65 0.20
Southern2.30 1.92 0.38 0.56
Combined1.67 1.72 -‐0.05 0.82
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
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Results: Ilevo – 2015
“Ilevo” Yield “PV” Yield“Ilevo” Yield
minus “PV”
YieldP -‐ value
Northern 68.8 68.7 0.1 0.98
Central70.7 70.1 0.6 0.80
Southern58.4 58.7 -‐0.3 0.91
Combined65.9 65.8 0.1 0.77
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
Results: Ilevo – 2016
“Ilevo” RF “PV” RF“Ilevo” RF minus
“PV”
RFP -‐ value
Northern 6.11 9.09 -‐2.98 0.33
Central7.51 5.84 1.67 0.29
Southern0.99 1.27 -‐0.28 0.32
Combined4.87 5.40 -‐0.53 0.53
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
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Results: Ilevo – 2016
“Ilevo” Yield “PV” Yield“Ilevo” Yield
minus “PV”
YieldP -‐ value
Northern 80.6 78.1 2.5 0.03
Central75.0 75.1 -‐0.1 0.92
Southern64.9 65.8 -‐0.9 0.81
Combined73.5 73.0 0.5 0.34
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
Results: Ilevo – 2015 – 2016
“Ilevo” RF “PV” RF“Ilevo” RF minus
“PV”
RFP -‐ value
Northern 3.69 5.12 -‐1.43 0.17
Central4.48 3.98 0.50 0.49
Southern1.64 1.59 0.05 0.86
Combined3.27 3.56 -‐0.29 0.50
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
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Results: Ilevo – 2015 – 2016
“Ilevo” Yield “PV” Yield“Ilevo” Yield
minus “PV”
YieldP -‐ value
Northern 74.7 73.4 1.3 0.03
Central72.9 72.6 0.3 0.67
Southern61.6 62.2 -‐0.6 0.26
Combined69.7 69.4 0.3 0.35
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
SC
WC
NC NE
C EC
NW
SW SE
Discussion -‐ Ilevo§Reproductive factor§Variability
– individual locations
§Yield§Significant yield increase in
2016 and over all years
(Northern District)
§No significant yield increases across
other environments
§Variable over years and locations§Site
specific§Northern sites in 2016 may
have impacted overall effects
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§ List of all avail seed
treatments and MOABrand name Crop(s)Targeted
nematodesActive
ingredientMode
of actioncotton, corn, soybean all ppn
abamectin
inhibits nerve transmission
all all ppn harpin protein bolsters natural
plant defenses
cotton, corn, soybean all ppn Bacillus
firmus
repels nematodes from roots
soybean SCN Pasteuria nishizawae nematode parasite
soybean SCN, RKN fluopyram SDHI enzyme
inhibitor
cotton, corn, soybean
SCN, RKN,reniform, lesion
tioxazafen mitochondrial translation inhibitor
corn, soybean SCN, reniform, lesionBacillus
amylo-‐liquefaciens under investigation
susceptiblesoybean variety
resistantsoybean variety
Decline of SCN Resistance in Iowa
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bushels per acre
52.7
45.9
Yield and SCN ControlSCN-resistant vs Susceptible Soybean
Varieties
East Central Iowa(1,310 eggs/100 cm3 at planting)
0
2,000
4,000
6,000
8,000
10,000 eggs per 100 cm3soil at
harvest
bushels per acre
52.7
45.9
2,169
8,875
SCN
Yield and SCN ControlSCN-resistant vs Susceptible Soybean
Varieties
East Central Iowa(1,310 eggs/100 cm3 at planting)
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● SCN resistance requires several genes
(Rhg genes) in the soybean plant
● no legal definition for SCN
resistance in US
● no government verification of SCN
resistance in US
● scientific definition of resistance
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01002003004005006007008009001000
Number of SCN-resistant Soybean Varieties Available for Iowa (MG
0-3)
1991 - 2016Num
ber of varieties
956
29
Registered Germplasm Lines that areSources of SCN Resistance for
Breeding
• PI 548402 (Peking)• PI 88788• PI 90763• PI 437654
There are many other soybean breeding lines with different
sources of resistance to SCN identified and released by breeders as
well.
• PI 209332• PI 89772• PI 548318 (Cloud)
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01002003004005006007008009001000
01002003004005006007008009001000
PI 88788Other
Num
ber of varieties
Number of SCN-resistant Soybean Varieties Available for Iowa (MG
0-3)
1991 - 2016
927*
29**
956
* 927 of 956 varieties have PI 88788 source of SCN
resistance
29
** 26 of 29 non-PI 88788 varieties have Peking source of SCN
resistance
*** almost all new soybean varieties have PI 88788 SCN
resistance
What would happen if a single herbicidewas used over and over
again for 20 years???
Glyphosate-susceptible (left) and glyphosate-resistant (right)
common ragweed populations three weeks after application of 44
oz/acre of Roundup PowerMax.Source: University Nebraska-Lincoln
CropWatch
~3 percent survival 100 percent survival
same thing happening with
PI 88788 SCN resistance
percent SCN reproduction on SCN-resistant variety
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Iowa State University SCN-resistant Soybean Variety Trial
Program
From 1991 to 1999, almost all SCN populations in variety trial
fields had
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y = -0.3798x + 59.726R² =
0.14294
0
10
20
30
40
50
60
70
80
90
0 10 20 30 40
SCN Reproductive Factor (Pf/Pi)
Yiel
d (b
u/ac
re)
each data point represents the MEAN yield of all resistant
varieties with PI 88788 in the variety trial field experiments
Build-up of SCN Numbers on PI 88788 versus Yield
McCarville et al., 2017
We are now losing soybean yield
to SCN with resistant varieties
and that will increase in the
future.
Prospects for the Future
• usefulness of traditional PI 88788 SCN resistance will
continue to decline – but keep using resistant varieties
PI 88788 resistantsoybean variety PI 88788 resistant
soybean variety
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Prospects for the Future
• usefulness of traditional PI 88788 SCN resistance will
continue to decline – but keep using resistant varieties
• new commercial varieties with non-PI 88788 resistance not very
likely
susceptiblesoybean variety
PI 88788 resistantsoybean variety
$0.00Photo: University of Minnesota
Thank you!
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