Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Potato (Solanum tuberosum) -- Rhizoctonia Canker (Black Scurf)
 
Cause: Rhizoctonia solani, a fungus that is in most soils and has a wide host range. Seed pieces can carry the fungus.
Symptoms: When sprouts are infected before or soon after emergence, they may be killed by reddish to dark brown girdling cankers found on the stems at or below ground. If plants are infected later in their development, they may have reddish brown to brown lesions on stems, stolons, and roots. Aerial tubers may form on the stem. Leaf curl, like that caused by the Potato leafroll virus, may occur. Tubers may have black bodies (scurf) on the surface and they are not easily removed. While the bodies do not affect the tuber's interior, enough of them on the surface of potatoes being grown for the fresh market will cause rejection.

Stem lesions are characteristic of Rhizoctonia canker.

Black masses (scurf) can be seen on the tuber surface.

Reddish-brown to brown lesions can be seen on stems, stolons, and roots.

 
Cultural control:
  1. Rotate out of potatoes if possible, preferably for 3 years.
  2. Shallow planting followed by gradual hilling-up speeds emergence and reduces damage.
  3. Avoid overirrigating early in the season. Cooling soil with irrigation slows emergence and favors the fungus.
  4. If possible, avoid seed lots that contain sclerotia.
  5. Warm seed before planting.
  6. To encourage more rapid emergence, plant deep but cover with a shallow layer of soil.
  7. The disease may be more severe when following sugar beets, alfalfa, or clover that was plowed down the spring of planting.
Chemical control:
  1. Amistar at 0.125 to 0.25 oz/1000 row feet applied in a 7” or less band either in-furrow at planting or as a directed spray at cultivation. 4-hr reentry.
  2. Blocker 4F at 5 to 10 pt/A in 10 to 20 gal/A of water, based on a 34-inch row spacing. Spray in furrow over seed. 12-hr reentry.
  3. Evito 480 SC at 0.16 to 0.24 fl oz/1000 ft row. Do not apply within 7 days of harvest. Oregon, Washington, and Idaho only (SLN OR-080034,SLN WA-080011, SLN ID- 080006) 12-hr reentry.
  4. Evolve Potato Seed-Piece Treatment (Tops MZ-Curzate) at 0.75 lb/100 lb seed-pieces.
  5. Headline at 0.4 to 0.8 fl oz/1000 row feet. Apply spray in furrow at planting. 12-hr reentry.
  6. Maxim or Maxim MZ Potato Seed Protectant at 0.5 lb/100 lb seed-pieces.
  7. Maxim 4FS at 0.08 to 0.16 oz/100 lb seed-pieces. 12-hr reentry.
  8. Moncut 70DF at 0.75 to 1.0 lb/A in furrow in at least 5 gal water/A. Rotation crop restrictions on label. 12-hr reentry.
  9. Quadris Flowable at 0.4 to 0.8 fl oz/1000 row feet applied in a 7” or less band either in furrow at planting or as a directed spray at cultivation. 4-hr reentry.
  10. Quadris Ridomil Gold at 0.82 fl oz/1000 row feet applied in furrow using 3 to 15 gal water/A. See label for reentry intervals.
  11. 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. T-22 Planter Box at 1 to 3 oz/100 lb seed- pieces is registered in Washington. Do not use in alkaline soils or if soil is below 50°F.
Content edited by: Phil Hamm and Cynthia M. Ocamb on January 1, 2010
 
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