By P. B. Hamm and C. M. Ocamb
Cause Fusarium spp. and Pectobacterium carotovorum are commonly found when seed piece decay is present. Fusarium may invade the cut surface of seed tubers, especially when cut seed is held for extended periods before planting, followed by an invasion of Pectobacterium. Other pathogenic organisms may be present. Seed piece decay also can be a problem when planting in cool, wet soils, which impairs suberization of the cut surface, particularly when cold seed is planted into warmer ground. The cultivar 'Shepody' may be more prone to this problem. Usually good quality seed, when properly stored and handled, rarely has this problem when correctly planted.
Symptoms A dry or slimy rot of the tubers. Poor, irregular stands in the field also are a result of this disease.
- Use high quality seed and warm to 50°F before cutting; avoid old tubers or tubers that are physiologically aged.
- Disinfest seed cutting equipment, especially between seed lots.
- Plant seed as soon as possible after cutting or hold cut seed 3 to 4 days at 50°F to 60°F and 85% to 90% humidity. Ensure that seed temperatures are higher than soil temperatures at planting.
- Store cut seed in open containers or crates for best possible ventilation. If using burlap bags, fill only halfway and stack for good ventilation.
- Avoid irrigation before plant emergence.
Chemical control Seed piece treatment for fungal decay.
- Dithane DF Rainshield at 1.25 lb/50 gal water used as a soak.
- Evolve Potato Seed Piece Treatment at 0.75 lb/100 lb seed pieces.
- Maxim MZ at 0.5 lb/100 lb seed pieces or Maxim 4FS at 0.08 to 0.16 oz/100 lb seed pieces. 12-hr reentry for Maxim 4FS; 24-hr reentry for Maxim MZ.
- Bio-Save 10 LP and Bio-Save 11 LP are registered for control of Fusarium dry rot, research in Montana and Idaho has shown this product to substantially reduce losses. Store product under refrigeration or in the freezer until used. Add 250 g of Bio-Save 10 LP to 15 gal of non-chlorinated water to treat 1500 sacks (100 lb apiece). Add 250 g of Bio-Save 11 LP to 40 gal of non-chlorinated water (1 gal treats 2,000 to 4,000 lb of tubers).
- T-22 HC at 0.5 to 3 oz/100 lb seed pieces will suppress certain fungal pathogens including Fusarium, Rhizoctonia, and Pythium spp. Do not use in alkaline soils or if soil is below 50°F. 4-hr reentry. O
References Jacobsen, B. 1999. Montana Crop Health Report, Montana State University Extension Service Vol. 12, No. 8.
Strand, L. 2006. Integrated Pest Management for Potatoes in the Western United States, 2nd edition. UC Agriculture and Natural Resources Publication 3316. 167 pp.