Cranberry (Vaccinium macrocarpon)-Phytophthora Root and Runner Rot

Cause Although three Phytophthora spp. have been found in Oregon and Washington beds, P. cinnamomi is the most pathogenic. These fungus-like microorganisms have spores that swim to healthy plants, enter them, and destroy roots and runners under flooded conditions. Most beds with root rot were wet picked; root rot in dry-picked beds occurs in areas with poor drainage.

Symptoms Dead spots in the bed occur first in poorly drained areas. Dead spots continue to expand to healthy areas. Plants at the margin may be stunted, usually have reddened foliage, and exhibit unthrifty growth. Lower (underground) runners have a red to olive-brown discoloration and lack feeder roots. Newly planted vines also die.

Cultural control Focus on these methods first.

  • Improve drainage in low areas of the bed.
  • Sand-in and replant poorly growing and low areas.
  • Uniform application of sprinkler irrigation will help avoid excessive water.
  • Maintain ditches and drains around the beds.
  • Construct new beds so that the crown is high enough to drain adequately into surrounding ditches or install internal drains.

Chemical control Use if needed but rotate materials from different groups to prevent or delay the occurrence of resistant fungi. Resistance to Group 4 fungicides has been detected in New Jersey.

  • Aliette WDG at 5 lb/A. Do not mix with surfactants or foliar fertilizers or use with copper products. Do not apply within 3 days of harvest. Do not use with adjuvants. Group P7 fungicide. 24-hr reentry.
  • Fosphite at 1 to 3 quarts/A. Do not use copper products within 20 days of treatment and do not use spray adjuvants. Group P7 fungicide. 4-hr reentry.
  • Fungi-Phite at 1 to 2 quarts/A. Group P7 fungicide. 4-hr reentry.
  • OxiPhos at 2.5 to 5 quarts/A as a foliar spray. Group P7 fungicide. 4-hr reentry.
  • Phostrol at 5 to 6 pints/A as a foliar spray. Do not apply within 3 days of harvest. Group P7 fungicide. 4-hr reentry.
  • ProPhyt at 4 pints/A. Group P7 fungicide. 4-hr reentry.
  • Rampart at 1 to 3 quarts/A. Group P7 fungicide. 4-hr reentry.
  • Ridomil Gold SL at 1 to 1.75 pints/A. Do not apply within 45 days of harvest. Apply first in fall after harvest, again in spring, and again 45 days before harvest. Use Ridomil Gold GR at 20 to 35 lb/A for spot treatment. Extend treated area 10 ft beyond the margin of weakened vines. Nontoxic to fish. Group 4 fungicide. 48-hr reentry.

References Polashock, J.J., Caruso, F.L., Averill, A.L., and Schilder, A.C. 2017. Compendium of Blueberry, Cranberry and Lingonberry Diseases and Pests. Second edition. St. Paul, MN: APS Press.

Polashock, J.J., Vaiciunas, J., and Oudemans, P.V. 2005. Identification of a new Phytophthora species causing root and runner rot of cranberry in New Jersey. Phytopathology 95:1237-1243.