Black Root Rot on Strawberries in Home Fruit Plantings

Rhizoctonia and Pythium species are the pathogens most commonly involved, as well as root-infecting nematodes. Environmental conditions that cause plant stress and increase susceptibility include drought, winter injury to the root system or crown, and freezing or waterlogging of the soil. This disease shows up most frequently in older plantings or areas that have had strawberries grown there more than once.

Symptoms and Disease Cycle

Symptoms include an uneven, "patchy" appearance in the strawberry bed. The first evidence of infection is the appearance of brown areas on the normally white or tan roots, but unless you dig the plants up, this isn't obvious. Eventually, death of the feeder rootlets will result and the older structural roots will blacken and deteriorate all the way through. Affected plants become stunted and produce few berries and runners.  It is important to note that strawberry roots do normally develop a dark surface as they age, but the roots will be firm and cream-colored if the surface is scraped off.

Disease Management

The disease most often occurs in "heavy" (clay) soils with a low organic matter content. Planting in well-drained, well-aerated soils such as those with a high organic matter content (greater than 6 percent if possible) is strongly recommended. Avoid compacting the soil and overwatering. Mulch to decrease winter injury, purchase disease-free plants, and allow 3 to 5 years before planting strawberries in the same area again.