Black root rot of strawberry is a disease complex of three or more fungi. Among the most damaging are Fusarium, Rhizoctonia and Pythium.  Pythium tends to predominate in sandy soils and Rhizoctonia on high clay content soils. Plants that have been under stress such as freezing, water logging, invasion of fungi or damage by nematodes (Pratylenchus spp.) are more susceptible to this disease.  Affected roots show a black discoloration and extensive death and do not function for water or nutrient uptake. Parts of the crown and lower leaves may also show black discoloration. See the photo below and Oregon State University Extension Plant Disease Online Guide.  Declining plant vigor and productivity are the most prevalent and typical symptoms of black root rot.
 
Unfortunately there is no cure for this disease. Management recommendations include:

• Use only healthy, white-rooted strawberries when planting
• Plant in well-drained soils
• Maintain plant vigor with adequate fertilization and cultivation
• Irrigate plants in dry periods

 
Fumigation may be practical for commercial plantings only, not for home plantings. There are no cultivars resistant to black root rot. Partial resistance might be observed depending on the predominant pathogen, type of soil and environmental conditions.
 
 

Black root rot of strawberry. Photo by Fanny Iriarte.