Scab (fungus – Fusicladium pyracanthae): Affects both the foliage and berries. It first shows up on foliage as small, greenish-yellow spots which later turn black. The berries are marked by small, black scabby spots. The disease is favored by long periods of intermittent rains and mild temperatures. Primary infection is from the previous year’s foliage. Control is obtained by following a regular spray program and sanitation through removal of plant residues.
Fire Blight (bacterium – Erwinia amylovora): Causes twig dieback and blossom blight. Infected blossoms wilt and turn black rapidly. The disease progresses from the blossoms into the vascular system where it causes extensive twig death. The foliage does not abscise due to the rapid rate of death. Twig blight is common and can result in dieback ranging up to 12-24 inches of twig length. Dark sunken areas or cankers are formed on the twigs. Bacteria overwinter in the cankers. In the spring, bacteria ooze from the cankers and are carried by wind, rain and insects to healthy foliage. Shrubs which have fire blight should be pruned to remove infected material. Make cuts four inches below visible cankers. All pruning equipment should be sterilized between cuts with a one part household bleach to nine parts of water. Avoid high nitrogen levels.
Sooty Mold: Black, powdery mold in patches or covering entire upper leaf surfaces. A non-parasitic growth resulting from infestations of aphids or other sucking insects. Use effective insect control.
Root Rots (fungus): Tip burn and/or marginal burn of leaves, often followed by branch dieback or death of entire plant. Frequently associated with poorly drained or waterlogged soils. (See the sections on Cotton Root Rot and Mushroom Root Rot)