1/13/17 Focus on Potato Webcast Powdery Scab and Potato Mop Top Virus Photo from Ueli Merz Photo from Uei Merz Photo from Ueli Merz Photo from Ueli Merz 1
1/13/17 Powdery Scab Disease Cycle Environmental conditions which favor disease: Cool, wet soil 2-6 F Alternating wet/dry conditions Excessive soil moisture (especially 3-4 wks 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 Effect of Seed on Powdery Scab Field selection Use clean seed Use resistant varieties Avoid over-watering during tuber initiation/early bulking Fungicides Omega? 2 1 Diseased Visually disease free Mini-tubers Trial 1 Trial 2 Tegg et al., 16, AJPR 93:231-238 2
1/13/17 Effect of Seed/Soil Inoculum on Powdery Scab 2 Fungicide Trial Root gall index 4 4 3 3 2 1 Dr. Rob Davidson, Practical Management of Powdery Scab, Focus on Potato 2 Fungicide Trial 2 Fungicide Trial Root gall index 4 4 3 3 2 1 Russet Burbank Tuber gall index 4 4 3 3 2 1 3 Fungicide Trial Minidoka, ID Fungicide Trial Tuber gall index 4 4 3 3 2 1 Tuber gall index 4 4 3 3 2 1 Air Chem Irr Air Chem Irr Irr Irr Irr 3
1/13/17 Two-nozzle design Dr. Rob Davidson, CSU Effect of Fluazinam (Omega) on Powdery Scab Dr. Rob Davidson, Colorado State, cv. Cherry Red % Infected Tubers 9 8 7 6 4 3 a a ab UTC Maxim (.8) Omega (1.), 1 nozzle 6 7 c Omega (1.), 2 nozzles d Maxim(.8) + Omega (1.), 2 NSD in 7 Dr. Rob Davidson, Practical Management of Powdery Scab, Focus on Potato % Unmarketable Tubers 4 4 3 3 2 1 Effect of Fluazinam (Omega) on Tuber Grade Dr. Rob Davidson, Colorado State, cv. Cherry Red a bc UTC Maxim (.8) Omega (1.), 1 nozzle b 6 7 bcd Omega (1.), 2 nozzles Dr. Rob Davidson, Practical Management of Powdery Scab, Focus on Potato cd Maxim(.8) + Omega (1.), 2 NSD in 7 A84118-3 Gem Russet Russet Norkotah MSG227-2 BO64-8 Bannock Russet Yukon Gold Ranger Russet Russet Burbank Alturas Liberator Superior BO766-3 Ida Rose Umatilla A986-11 B124-1 AF178-7 Atlantic FL 133 SC881-2 Chipeta Ivory Crisp Cultivar Susceptibility to Powdery Scab (Roots) 3 4 Root gall index Cultivar Susceptibility to Powdery Scab (Tubers) Russet Burbank Gem Russet Bannock Russet Russet Norkotah Umatilla A84118-3 MSG227-2 Ranger Russet Alturas BO64-8 A986-11 Superior Atlantic FL133 Yukon Gold B124-1 Ivory Crisp BO766-3 AF178-7 Liberator SC881-2 Ida Rose Chipeta Entries Most Resistant to Powdery Scab Root Galls 1. Gem Russet 2. Summit Russet 3. Russet Norkotah 4. MSG227-2. BO64-8 6. Bannock Russet 7. Yukon Gold 8. Ranger Russet 9. Russet Burbank. Alturas Tuber Lesions 1. Russet Burbank 2. Gem Russet 3. Bannock Russet 4. Russet Norkotah. Umatilla 6. Summit Russet 7. MSG227-2 8. Ranger Russet 9. Alturas. BO64-8 1 2 Tuber scab index 4
1/13/17 Summary Fungicides did not significantly reduce root galls or tuber scab lesions. Two nozzle application of Omega (1. pt) may offer some control. Potato Mop Top Virus Russet Burbank is one of the more resistant varieties to root and tuber lesions. How does PMTV live and survive? Is NOT spread by aphids. Infected seed does NOT lead to % infection of daughter tubers (self-eliminating). Vector = Spongospora subterranea (Powdery scab). Conditions favoring vector, favor PMTV. Survives in vector (soil) between -18 yrs. Only control is controlling vector. PMTV Symptoms Foliar symptoms NOT associated with primary infection. Symptoms favored by cool weather. Foliar = similar to calico Tuber = necrotic arcs (may require alternating storage temperatures to develop). Potato Mop Top Virus in Photo courtesy of Dr. Dave Lambert Potato Mop Top Virus in Photo courtesy of Dr. Dave Lambert
1/13/17 Potato Mop Top Virus in Russet Burbank Photo courtesy of Dr. Dave Lambert Potato Mop Top Virus Photo courtesy of Dave Lambert PMTV Look-alikes Corky ringspot (Tobacco rattle virus) Alfalfa mosaic virus PVY ntn strain (?) Alfalfa Mosaic Virus Potato Mop Top Virus Corky Ringspot Photo courtesy of Phil Hamm PVY ntn in Alturas Photo courtesy of Phil Hamm 6