Slight yellowing of the leaves followed quickly by permanent wilting and plant death are the symptoms usually associated with Phytophthora root rot on container-grown Kurume azaleas and rhododendrons in Alabama. In landscapes, established plants may show symptoms of general decline for one or more years before succumbing to root rot, while newly planted azaleas will quickly die. The foliage of azaleas and rhododendrons may also be invaded by some Phytophthora root rot fungi. Irregular blotches which are first olive-colored and later brown, sometimes with a red margin, develop on the leaves. Diseased leaves are usually shed by the plant.
Damage usually appears on limbs near the base of the plant.
Disease Cycle Phytophthora root rot is caused by several species of fungi in the genus Phytophthora . Several other Phytophthora species, including P. parasitica , P. citricola , and possibly P. cactorum , are also known to attack woody plants, particularly azaleas and rhododendrons. Phytophthora root rot fungi are present in virtually every nursery in Alabama. These fungi are easily introduced into a nursery on anything from rooted cuttings to container stock, as well as by infested soil or potting media. The resting structures are released into the soil or potting media from infested crop debris and are readily spread from pot to pot throughout propagation and container production areas by soil and splashing water.