Powdery Scab and PMTV

2/23/2021

Management of Powdery Scab and Potato Mop Top Virus

Jeff Miller, James Woodhall, and Nora Olsen

S pongosporasubterraneasubsp. subterranea(Protozoa)

Photo from Ueli Merz Photo from Ueli Merz Photo from Ueli Merz

Photo from Ueli Merz

1 2/23/2021

2 2/23/2021

3 2/23/2021

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 to develop). – Can look like TRV, PVYntn, internal brown spot • Symptoms increase with time in storage • Can cause external symptoms

TRV PMTV

Photos courtesy of Jonathan Whitworth Which one is PMTV? TRV?

4 2/23/2021

Photo courtesy of Jonathan Whitworth

PMTV Positive

5 2/23/2021

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

6 2/23/2021

Effect of Seed on Powdery Scab

0 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

7 2/23/2021

Use of Fertility/Fungicides

• Sulfur • Manganese • Zinc salts

• Mancozeb • Metam fumigation • Chloropicrin • Fluazinam (Omega)

2002 Fungicide Trial Rexburg, ID

Shepody 45 40

x 35 e

d 30 n i

l 25 a g

20 t

o 15 o

R 10 5 0

8 2/23/2021

2002 Fungicide Trial Rexburg, ID

Russet Burbank 45 40

x 35 e

d 30 n i

l 25 a g

20 t

o 15 o

R 10 5 0

2002 Fungicide Trial Rexburg, ID

Shepody 45 40

x 35 e d

n 30 i

l l 25 a g 20 r e

b 15 u

T 10 5 0

9 2/23/2021

2003 Fungicide Trial Minidoka, ID

Shepody 45 40 35 x e

d 30 n i

l 25 a g

r 20 e

b 15 u T 10 5 0 UTC Rid Gold Rid Gold Rid Gold Phostrol Phostrol Phostrol Omega Gavel Moncut MZ MZ MZ Air Chem Irr Air Chem Irr Irr Irr Irr

2005 Fungicide Trial Rexburg, ID Shepody 45 40 35 x

e 30 d n i

l 25 a g

r 20 e b

u 15 T 10 5 0 UTC Evolve (12) Forum IF Forum Fol Headline IF Headline Rid Gold Bli-nix Fosphite (6) (6) (9) Fol (9) Bravo + Phostrol

10 2/23/2021

Effect of Fluazinam (Omega) on Powdery Scab Dr. Rob Davidson, Colorado State, cv. Cherry Red

90 a 80 a 70 ab s r e

b 60 c u T 50 d e

t d

c 40 e f n

I 30

% 20 10 0 UTC Maxim (0.08) Omega (1.5), 1 Omega (1.5), 2 Maxim(0.08) + nozzle nozzles Omega (1.5), 2 2006 2007 NSD in 2007

Dr. Rob Davidson, Practical Management of Powdery Scab, Focus on Potato

Effect of Fluazinam (Omega) on Tuber Grade Dr. Rob Davidson, Colorado State, cv. Cherry Red

50 a 45 s r

e 40 b

u 35 T

e l 30 bc b b a t 25 e k

r bcd

a 20 cd m

n 15 U 10 % 5 0 UTC Maxim (0.08) Omega (1.5), 1 Omega (1.5), 2 Maxim(0.08) + nozzle nozzles Omega (1.5), 2 2006 2007 NSD in 2007

Dr. Rob Davidson, Practical Management of Powdery Scab, Focus on Potato

11 2/23/2021

Effect of Chemical Treatment on Scab and PMTV

Russet Norkotah Line 8 Canela Russet 60 90

80 50 70

40 60 e e c c

n n 50 e e d d

i 30 i c c n n

I I 40

% % 20 30

20 10 10

0 0 Tubers w/ Ps PMTV w/ PS PMTV w/o PS Tubers w/ Ps PMTV w/ PS PMTV w/o PS Omega RIDEZ Control Omega RIDEZ Control

Zeng et al., 2020, Plant Disease 104:2807-2816

Two-nozzle design – Dr. Rob Davidson, CSU

12 2/23/2021

Theory behind broadcast application

Theory behind in-furrow application

13 2/23/2021

Effect of Fumigation on Powdery Scab

70 l o r t n 60 o C s

v 50 n o i t 40 c u d e 30 R

% 20

0 Chloropicrin (178 lb/a) Chloropicrin (356 lb/a) PIC 33% + DCP 66% (267 lb/a) PIC 33% + DCP 66% (445 lb/a) 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

14 2/23/2021

Cultivar Susceptibility to Powdery Scab in Idaho Haynes et al., AJPR 82:73 and 83:113

Summit Russet Russet Burbank Gem Russet Gem Russet Russet Norkotah Bannock Russet Harley Blackwell Russet Norkotah Bannock Russet Umatilla Yukon Gold Summit Russet Ranger Russet Ranger Russet Russet Burbank Alturas Alturas Harley Blackwell Liberator Defender Superior Superior Ida Rose Atlantic Umatilla FL1533 Defender Yukon Gold Atlantic Ivory Crisp FL 1533 Liberator Chipeta Ida Rose Shepody Chipeta Ivory Crisp Shepody

0 10 20 30 40 0 5 10 15 20 25

Root gall index Tuber scab index

Bittara and Robinson, Powdery Scab of Potatoes, PP1891, June 2018.

15 2/23/2021

Cultivar susceptibility to PMTV symptoms (NDSU)

Sensitive (>15%) Moderately Sensitive Moderately Insensitive Insensitive (<5%) (10-15%) (5 -10%) 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

100 a a a ab 90 bc 80 c d

e 70 t

c d e

f 60 f A

s 50 t n

a 40 l

P e 30 % 20 10 0 Burbank Ranger Norkotah 296 Alturas Umatilla Teton Clearwater Dakota

16 2/23/2021

Powdery Scab - Variety Severity (0-5)

2.5 a

2 b

e bc l c a c 1.5 S y t i r d e d v 1 e S e 0.5 f

0 Burbank Ranger Norkotah 296 Alturas Umatilla Teton Clearwater Dakota

PMTV - Variety % Incidence of visible symptoms

25 a a d e t

c 20 e f f A

s 15 r e b u T

% b 5 c c c c c 0 Burbank Ranger Norkotah 296 Alturas Umatilla Teton Clearwater Dakota

Interaction between variety and treatment was not significant.

17 2/23/2021

Effect of Chemical Treatment on Scab and PMTV

Russet Norkotah Line 8 Canela Russet 60 90

80 50 70

40 60 e e c c

n n 50 e e d d

i 30 i c c n n

I I 40

% % 20 30

20 10 10

0 0 Tubers w/ Ps PMTV w/ PS PMTV w/o PS Tubers w/ Ps PMTV w/ PS PMTV w/o PS Omega RIDEZ Control Omega RIDEZ Control

Zeng et al., 2020, Plant Disease 104:2807-2816

Soil Moisture – Powdery Scab and PMTV

Powdery scab PMTV Tuber Necrosis 35 20 a a 18 30 a 16

e 25 e c c 14 ab n n e e

d d 12 b i 20 b i c c n n I I b 10 r r

e 15 e b b 8 u u T T

% % 6 10 c 4 5 2 0 0 Wet Dry, wet Wet, dry Dry Wet Dry, wet Wet, dry Dry Domfeh and Gudmestad, 2016

18 2/23/2021

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