Pacific Northwest 1998 An Online Guide to Plant Disease Control

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Potato (Solanum tuberosum) -- Fusarium Dry Rot
 
Cause: Several Fusarium sp. including F. sambucinum (Fs), F. solani var. coeruleum (Fsc) and F. avenaceum (Fa). These fungi survive on refuse and live in soil. Infections can originate from infested seed tubers. Tuber rot usually does not occur unless the tuber is injured during harvest. Wounds provide a way for the fungus associated with soil to enter the tuber. Dry rot is one of the most common storage diseases in Idaho. Fusarium dry rot leads to secondary infections by soft rot bacteria.
Symptoms: A dry rot of the tuber starts from a wound or bruise and is at first small and brown. Mold on the rotting tuber may be white, rose, or violet. As the rot progresses, a cavity begins to form, the tuber mummifies and ultimately only the dry shell persists. Lesions from F. solani< var. coeruleum infection start at the side of the infection and progress in a fairly uniform manner through the tuber. As lesions age, rots turn yellow to brown. Lesions caused by F. sambucinum tend to be very dark brown to black and progress through the tuber in a very irregular manner sometimes called "tunneling."

Note the dry rot with a whitish mold.

 
Cultural control:
  1. Be sure tubers mature and skins are well "set" before harvest.
  2. Avoid wounding and bruising tubers by handling carefully.
  3. Harvest during dry, cool weather.
Chemical control: Apply fungicides as tubers enter storage. Caution In some locations, some strains of Fusarium have developed resistance to the benzimidazoles such as Decco Salt No. 19, Mertect 340-F, TBZ, and Tops 5.

  1. Decco Salt No. 19 at 5.67 g/2,000 lb of potatoes.
  2. Evolve (Tops MZ-Curzate) Potato Seed-Piece Treatment at 0.75 lb/100 lb seed-pieces.
  3. Maxim at 0.5 lb/100 lb seedpieces. Note Fludioxonil (Maxim) has a site specific mode of action and fungicide resistance is a possibility if this product is not used accordingly to the label.
  4. Maxim MZ at 0.5 lb/100 lb seed-pieces or Maxim 4FS at 0.08 to 0.16 oz/100 lb seed-pieces.
  5. Mertect 340-F at 0.42 fl oz/2,000 lb of unwashed tubers on a conveyor line with tumbling action. Tubers should tumble to ensure complete coverage. If another treatment is necessary before cutting and shipping seed tubers, mist at the same rate as above or soak 20 sec in 42 fl oz/100 gal water. Adding water in these sprays requires drying potatoes after treatment. Run the air system without humidification until all tuber surfaces are dry, even within the pile.
  6. Tops MZ at 0.75 to 1 lb/100 lb seed-pieces. Tops MZ-Gaucho is registered for use by commercial seed treaters only.
Biological control:
  1. Bio-Save 110 and Bio-Save 10LP are registered for control of Fusarium dry rot, research in Montana and Idaho have shown this product to substantially reduce losses. Store product at -70°F or on dry ice until used. Add 250 g product to 40 gal of water and drip or spray overhead prior to storage.
  2. T-22 Planter Box at 1 to 3 oz/100 lbs seed- pieces is registered is registered in Washington. Do not use in alkaline soils or if soil temperature is below 50°F.
References:
Jacobsen, B. 1999. Montana Crop Health Report, Montana State University Extension Service Vol. 12, No. 8.

Ocamb CM., Hamm, PB. and Johnson, DA. 2006. Benzimidazole resistance of Fusarium species recovered from potatoes with dry rot from storages located in Columbia Basin of Oregon and Washington. American Journal of Potato Research:84:169-177.

Content edited by: Cynthia M. Ocamb on January 1, 2010
 
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