Pacific Northwest 1998 An Online Guide to Plant Disease Control

FactSheets offer superior print quality for the page you are currently viewing. Using Microsoft's Internet Explorer has given best printing results.
Glossary
Guide Home
Search

OSU Extension Office
 
Potato (Solanum tuberosum) -- White Mold (Sclerotinia Stem Rot)
 
Cause: A fungus, Sclerotinia sclerotiorum, that overwinters in soil as hard black sclerotia. Sclerotia germinate in spring and produce small, inverted, mushroom-like structures called apothecia that shoot spores into potato foliage where they infect potato leaves and stems. Sclerotia can also directly germinate and infect the plant. Though widespread, and at times appearing to be quite damaging, the effect of yield is likely marginal in most fields, particularly in the Columbia Basin.
Symptoms: First, vines in the field rapidly wilt and die due to a soft decay near the crown. The decayed area becomes covered with white mycelium and hard black fungal sclerotia. Sclerotia commonly occur inside stems. The stem becomes a light brown in color to white and brittle after infection. At times, small inverted trumpet-shaped structures called apothecia can be found under the vine cover following row closure but these are difficult to see.

Note the white mycelium along this stem lesion.

Note the dark sclerotium, characteristic of white mold.

 
Cultural control:
  1. It may help to reduce humidity within the vines by increasing spacing, decreasing vine growth, and irrigating less frequently.
Chemical control: The disease must be severe for fungicide application to be economically effective.
  1. Blocker 4 F at 3 to 7.5 pints/A at 7- to 10-day intervals. Foliar applications of Blocker 4F cannot be made if Blocker or other PCNB products were used in-furrow at planting. Do not apply within 45 days of harvest, shorter preharvest interval with reduced rates. Registered for use in Oregon, Washington, and Idaho only ( SLN OR-030015, SLN WA-030014, and SLN ID-030008). 12-hr reentry.
  2. Botran 5 F at 1.2 to 3.6 quarts/A. Begin treatment at first flower drop, or at approximately the time of full bloom of primary flower inflorescences. If disease persists, subsequent applications may be made at 7- to 10-day intervals. Chemigation is the preferred method of application. Do not apply within 20 days of harvest. 12-hr reentry. Apply with the following equipment:

    Sprinkler Irrigation - See APPLICATION THROUGH SPRINKLER IRRIGATION EQUIPMENT for specific instructions.

    In Oregon and Idaho, apply as a directed spray to the base of plants and adjacent soil surface using drop nozzles. Use at least 30 gal/A water. Do not spray upper canopy of foliage as this may cause minor leaf bronzing. If canopy is to be sprayed, use at least 100 gal/A water. For use in Washington, see label for specific details. Do not apply within 20 days of harvest. 12-hr reentry.

  3. Endura at 5.5 to 10 oz/A at full bloom of primary flower inflorescences. Make a second application 14 days later if conditions continue to be favorable for disease development. Preharvest interval is 30 days. 12-hr reentry.
  4. Nevado 4F at 1 to 2 pints/A on 10- to 14-day intervals. Do not apply within 14 days of harvest. 24-hr reentry.
  5. Omega 500 F at 5.5 to 8 fl oz/A on 7- to 10-day intervals beginning at row closure or when flowers begin to fall. Do not apply within 14 days of harvest. 48-hr reentry; 96-hr reentry for high exposure activities.
  6. Rovral 4 Flowable at 2 pints/A in at least 10 gal/A water. Do not apply by air for white mold control. Apply at first sign of disease or at full bloom of primary flower inflorescences and again 14 to 21 days later. (These applications also control early blight). Do not irrigate for 24 hours after application. Do not apply within 14 days of harvest. 24-hr reentry.
  7. T-Methyl 4.5F AG at 20 to 30 fl oz/A. Make first application at full bloom of primary flower inflorescences and repeat on 7- to 14-day intervals. May be applied by ground or air. Preharvest interval is 21 days. 12-hr reentry.
  8. Topsin M WSB at 1 to 1.5 lb/A on 7- to 14-day intervals. Make first application at full bloom of primary flower inflorescences. Do not apply within 21 days of harvest. Aerial application is not recommended for control of this disease on this crop. 12-hr reentry
References:
Johnson, DA. and Atallah, ZK. 2006. Timing fungicide applications for managing Sclerotinia stem rot of potato. Plant Dis. 90:755-758.
Content edited by: Phil Hamm and Cynthia M. Ocamb on January 1, 2010
 
Top

In print since 1954 and on the web since 1996. Questions or comments, please contact us.