Red stele, or red core, is the most serious disease of strawberry. In areas with cool, moist soil conditions, especially soils heavy in clay that are saturated with water during cool weather, the disease is more prevalent. Red stele is caused by the soil-inhabiting fungus Phytophthora fragariae.

Symptoms and Disease Cycle

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 amount of diseased roots increase, plant size, yield, and berry size decrease.

Strawberry patch infested with the Red Stele pathogen

Healthy strawberry patch

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. 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. A few days after infection, roots begin to rot, more spores are produced by the fungus within this rotted tissue, and eventually, the spores and the rottedroots become incorporated into the soil.

Management

Because the spores of this pathogen can travel long distances in surface water, it is important to maintain good drainage in strawberry beds which also minimizes runoff. It is also necessary to avoid soil compaction. The purchasing of planting stock that has been inspected and tested for P. fragariae as well as planting disease-resistant varieties is recommended for the control of this root rot.