2/23/2021
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Management of Powdery Scab andPotato Mop Top Virus
Jeff Miller, James Woodhall, and Nora Olsen
Photo from Ueli MerzPhoto from Ueli Merz
Photo from Ueli Merz
Photo from Ueli Merz
S pongosporasubterraneasubsp. subterranea(Protozoa)
2/23/2021
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PMTV
• Foliar symptoms not associated with primary infection.
• Foliar = similar to calico.
• Symptoms favored by cool weather.
• Tuber = necrotic arcs (may require alternating storage temperatures todevelop).
– Can look like TRV, PVYntn, internal brown spot
• Symptoms increase with time in storage
• Can cause external symptoms
Photos courtesy of Jonathan Whitworth
Which one is PMTV? TRV?
PMTVTRV
2/23/2021
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Powdery Scab Disease Cycle
• Environmental conditions which favor disease:
– Cool, wet soil
– 52-65°F
– Alternating wet/dry conditions
– Excessive soil moisture (especially 3-4 weeks after TI)
• Sandy soils and poor drainage more conducive for disease.
• Tuber infection typically occurs at tuber initiation.
• Very little inoculum required to cause disease.
Powdery Scab Management
• Longer crop rotation - > 5 years (12 year survival).
• Avoid planting in contaminated, poorly drained soils.
• Plant disease-free seed in disease-free areas.
• Avoid using manure if animals ingested infected tubers.
• Plant resistant cultivars.
• Carefully manage irrigation water.
• Use of fertility, pesticides?
Compendium of Potato Diseases, 2nd Ed.Falloon, AJPR (2008) 85:253-260
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Effect of Seed on Powdery Scab
0
5
10
15
20
25
Diseased Visually disease free Mini-tubers
Trial 1 Trial 2
Tegg et al., 2016, AJPR 93:231-238
Effect of Seed/Soil Inoculum on Powdery Scab
Dr. Rob Davidson, Practical Management of Powdery Scab, Focus on Potato
2/23/2021
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Use of Fertility/Fungicides
• Sulfur
• Manganese
• Zinc salts
• Mancozeb
• Metam fumigation
• Chloropicrin
• Fluazinam (Omega)
2002 Fungicide TrialRexburg, ID
05
1015202530354045
Ro
ot
gall
ind
ex
Shepody
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2002 Fungicide TrialRexburg, ID
05
1015202530354045
Ro
ot
gall
ind
ex
Russet Burbank
2002 Fungicide TrialRexburg, ID
05
1015202530354045
Tub
er
gall
ind
ex
Shepody
2/23/2021
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2003 Fungicide TrialMinidoka, ID
0
5
10
15
20
25
30
35
40
45
UTC Rid GoldMZ
Rid GoldMZ
Rid GoldMZ
Phostrol Phostrol Phostrol Omega Gavel Moncut
Tub
er
gall
ind
ex
Shepody
AirAir Chem Chem Irr Irr Irr IrrIrr
2005 Fungicide TrialRexburg, ID
0
5
10
15
20
25
30
35
40
45
UTC Evolve (12) Forum IF(6)
Forum Fol(6)
Headline IF(9)
HeadlineFol (9)
Rid GoldBravo +Phostrol
Bli-nix Fosphite
Tub
er
gall
ind
ex
Shepody
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Effect of Fluazinam (Omega) on Powdery ScabDr. Rob Davidson, Colorado State, cv. Cherry Red
aa
ab
c
d
0
10
20
30
40
50
60
70
80
90
UTC Maxim (0.08) Omega (1.5), 1nozzle
Omega (1.5), 2nozzles
Maxim(0.08) +Omega (1.5), 2
%In
fect
edTu
ber
s
2006 2007NSD in 2007
Dr. Rob Davidson, Practical Management of Powdery Scab, Focus on Potato
Effect of Fluazinam (Omega) on Tuber GradeDr. Rob Davidson, Colorado State, cv. Cherry Red
a
bc b
bcdcd
0
5
10
15
20
25
30
35
40
45
50
UTC Maxim (0.08) Omega (1.5), 1nozzle
Omega (1.5), 2nozzles
Maxim(0.08) +Omega (1.5), 2
%U
nm
arke
tab
leTu
ber
s
2006 2007NSD in 2007
Dr. Rob Davidson, Practical Management of Powdery Scab, Focus on Potato
2/23/2021
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Effect of Chemical Treatment on Scab and PMTV
0
10
20
30
40
50
60
Tubers w/ Ps PMTV w/ PS PMTV w/o PS
%In
cid
ence
Russet Norkotah Line 8
Omega RIDEZ Control
0
10
20
30
40
50
60
70
80
90
Tubers w/ Ps PMTV w/ PS PMTV w/o PS
%In
cid
ence
Canela Russet
Omega RIDEZ Control
Zeng et al., 2020, Plant Disease 104:2807-2816
Two-nozzle design – Dr. Rob Davidson, CSU
2/23/2021
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Effect of Fumigation on Powdery Scab
0
10
20
30
40
50
60
70
80
90
Chloropicrin (178 lb/a) Chloropicrin (356 lb/a) PIC 33% + DCP 66% (267 lb/a) PIC 33% + DCP 66% (445 lb/a)
%R
edu
ctio
nvs
Co
ntr
ol
Plastic Cover No Cover
Tsror (Lahkim) et al., 2019, Crop Protection 124:104836
Metam Sodium on Powdery Scab
• Water-applied Metamor (51% MS):
– 68% reduction at 46 gal/acre (=56 gal Vapam)
– 80% reduction at 66 gal/acre (=80 gal Vapam)
• Data for ground application
– Significant PS reported under metam-fumigated conditions
• More research needed in southern Idaho conditions
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Cultivar Susceptibility to Powdery Scab in Idaho
0 10 20 30 40
Ivory Crisp
Shepody
Chipeta
FL 1533
Atlantic
Defender
Umatilla
Ida Rose
Superior
Liberator
Alturas
Russet Burbank
Ranger Russet
Yukon Gold
Bannock Russet
Harley Blackwell
Russet Norkotah
Gem Russet
Summit Russet
Root gall index
0 5 10 15 20 25
Shepody
Chipeta
Ida Rose
Liberator
Ivory Crisp
Yukon Gold
FL1533
Atlantic
Superior
Defender
Harley Blackwell
Alturas
Ranger Russet
Summit Russet
Umatilla
Russet Norkotah
Bannock Russet
Gem Russet
Russet Burbank
Tuber scab index
Haynes et al., AJPR 82:73 and 83:113
Bittara and Robinson, Powdery Scab of Potatoes, PP1891, June 2018.
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Cultivar susceptibility to PMTV symptoms (NDSU)
Sensitive (>15%) Moderately Sensitive(10-15%)
Moderately Insensitive(5 -10%)
Insensitive (<5%)
Dark Red Norland Red Norland Alpine Russet Red Gold
Modoc Chieftain Ciklamen Red Tumb
Viking Snowden Dakota Ruby Colorado Rose
Dakota Crisp Red La Soda Bintje
Yukon Gold LaMoka
Alturas
Most russets
Powdery Scab - Variety% Incidence
a
bcc
d
a a
e
ab
0
10
20
30
40
50
60
70
80
90
100
Burbank Ranger Norkotah 296 Alturas Umatilla Teton Clearwater Dakota
%P
lan
tsA
ffec
ted
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Powdery Scab - VarietySeverity (0-5)
bc
d d
e
a
b
f
c
0
0.5
1
1.5
2
2.5
Burbank Ranger Norkotah 296 Alturas Umatilla Teton Clearwater Dakota
Seve
rity
Scal
e
PMTV - Variety% Incidence of visible symptoms
cc
c
a
c c
b
a
0
5
10
15
20
25
30
Burbank Ranger Norkotah 296 Alturas Umatilla Teton Clearwater Dakota
%Tu
ber
sA
ffec
ted
Interaction between variety and treatment was not significant.
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Effect of Chemical Treatment on Scab and PMTV
0
10
20
30
40
50
60
Tubers w/ Ps PMTV w/ PS PMTV w/o PS
%In
cid
ence
Russet Norkotah Line 8
Omega RIDEZ Control
0
10
20
30
40
50
60
70
80
90
Tubers w/ Ps PMTV w/ PS PMTV w/o PS
%In
cid
ence
Canela Russet
Omega RIDEZ Control
Zeng et al., 2020, Plant Disease 104:2807-2816
Soil Moisture – Powdery Scab and PMTV
a
a
b
b
0
5
10
15
20
25
30
35
Wet Dry, wet Wet, dry Dry
%Tu
ber
Inci
den
ce
Powdery scab
a
ab
b
c
0
2
4
6
8
10
12
14
16
18
20
Wet Dry, wet Wet, dry Dry
%Tu
ber
Inci
den
ce
PMTV Tuber Necrosis
Domfeh and Gudmestad, 2016
2/23/2021
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Summary
• More research needed on the effects of fertility (e.g. zinc, manganese)
• Fungicide performance is inconsistent at best.
– Two nozzle application of Omega (1.5 pt) may offer some control.
– Research needed on broadcast vs in-furrow.
• Fumigation was effective if covered (chloropicrin) or water-run (metam).
• Russet cultivars generally more resistant varieties to tuber lesions.
• Link between PS symptoms and PMTV symptoms not solid.
• Keeping soil dry = lower PS on tubers and PMTV symptoms