Root Rot in Photinia Shrubs

Disease Identification

• Photinia are susceptible to infection from a fungal, root rot disease caused by numerous Phytophthora fungi. These include P. cinnamomi, P. cactorum and P. citricola. The soil-borne disorder is more common in plants that are grown in consistently wet or poorly drained soils. Phytophthora root rot is the most destructive disease of woody ornamentals, according to the Alabama Cooperative Extension.

Cycle

• The fungi is introduced into the growing area either on the roots of newly bought plants, or is already present in soil in the form of resting structures that can linger for extended periods in the ground. These spores are activated in soil temperatures of 77 to 82 degrees F and excessively moist soil. The disease enters the plants through the roots and is spread to other plants in the area by the runoff from the primary site.

Damage

• The disease starts to damage the roots of plants, turning them brittle and brown in color and reducing their water and nutrient absorbing capacity. The plant crown is affected at the soil line and the trunk is girdled by the fungi at this point. Water-soaked, brown cankers appear on the lower trunk. The cankers often start to secrete a dark fluid or gum. Examination of wood under the bark reveals a reddish discoloration. Foliage starts to yellow, plants growth is stunted and there is limb dieback. This is followed by permanent wilting and gradual death of the entire plant.

Management

• There is no cure for phytophthora once the plant is infected, hence the best strategy is to use preventative measures to avoid disease from starting. Plant the photinia in a well-drained soil. Avoid the excessive use of nitrogen-rich fertilizers as this increases plant susceptibility to the disorder. Use resistant plant varieties and avoid planting in sites where the disease had occurred before. Apply recommended fungicides to soil prior to planting in these areas.