Phytophthora Blight

Figure 2. Phytophthora blight often invades the crown and causes a wet rot.

The symptoms of blight caused by this fungus, Phytophthora cactorum, may be confused with the symptoms produced by Botrytis sp. The stems, leaves, and buds can be affected by both diseases. However, with Phytophthora blight, there is no felty growth or sporulation on the plant surface when in a wet environment. Infected parts become dark brown or black and somewhat leathery. The entire shoot may turn black and die (Figure 2). Cankers may appear along the stems and cause them to fall over. While Botrytis sp seldom invades the crown, Phytophthora sp often does, causing a wet rot to develop and destroy the entire plant. Because infections of this disease generally occur in the roots and lower portions of the stem, spraying with fungicides is of little value. Confirmed cases should be removed and destroyed, together with adjacent soil. Planting healthy clumps in new locations where the soil is well drained usually prevents further trouble.