Black Root Rot
Black root rot is known as a "disease complex," meaning that it can be caused by several factors. This complex is associated with a number of pathogenic soil fungi (most commonly Rhizoctonia and Pythium species) and root-infecting nematodes; environmental conditions that can include drought, winter injury to the root system, and the freezing or waterlogging of the soil; nutrient deficiencies; fertilizer burn; pesticide injury; or a combination of all these factors. Most older plantings or replanted fields are affected.
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. Eventually, death of the feeder rootlets will result and the structural roots of the mother plant will blacken and deteriorate. As the disease progresses, the entire root will break off when bent, leaving a short stub at the crown. Affected plants become stunted and produce few berries and runners. Older infected roots are called "rattails."
The disease generally is associated with soil types of high clay content. Planting in well-drained, well-aerated soils such as those with a high organic matter content (greater than 6 percent) is strongly recommended. Soil compaction and excessive irrigation should be avoided. Mulching to decrease winter injury, purchasing disease-free plants, and rotating crops for 3 to 5 years also are methods of controlling black root rot. There are no fungicides for control.