The disease is caused by the soil-inhabiting fungus Phytophthora fragariae . Healthy roots are infected by spores produced from other infected plants. These spores can move through the soil and penetrate the tips of roots, growing within the root system. Frequently, the diseased area in the bed follows a definite pattern. Plants showing aboveground symptoms occur in patches where the soil is wettest.
Symptoms depend on the severity of the root rotting.
Severely diseased plants are stunted, with the younger leaves turning a blue-green and the older ones, red, yellow, or orange. Plants will eventually wilt and die. As the number of diseased roots increases, plant size, yield, and berry size decrease. When a young, infected root is cut open lengthwise, the stele or core above the rot is red. As the disease progresses, the lateral roots die, giving the main roots a rattail appearance.