Azalea Leaves With Black Fungus on Top

Sooty Mold

• Sooty mold is a name that's associated with a number of fungi, including members of the Capnodium, Fumago and Scorias families. The mold favors mild, wet weather and thrives on honeydew, a sweet substance that is the product of sap-sucking insects. The mold is not an infection and does not damage living tissue, which means it is not fatal to the plant. If left untreated it may decrease photosynthesis, which over time may decrease growth, but no serious side effects usually result. The associated insects usually have more harmful effects than the mold. Managing the sap-sucking insects is key to controlling sooty mold, which usually requires the application of an insecticide or the use of insecticidal soap or horticultural oils, depending on the pest. Most often, sooty mold will weather away once the pests are taken care of, or may be washed away with a strong stream of water.

Powdery Mildew

• Powdery mildew is a fungal problem that infects just about all types of plants around the world. It causes a white or dark gray substance to grow on leaves. Like sooty mold, it is not a disease, but a fungus that grows on the leaves. It most often starts as small spots, but will grow to take over the leaf. If left untreated, photosynthesis will suffer, growth may be reduced and leaves will often turn yellow, then black. Cultural control, including proper pruning and watering will help prevent the problem. An application of sulfur, neem oil or triforine will help chemically control the problem.

Black Spot

• Black spot is a fungal growth that is primarily found in roses, but may also affect azaleas. The problem starts as black spots on leaves, most frequently on the top surface. Wet conditions are required for growth, which means watering should be avoided during overcast or humid conditions. Cleaning up fallen debris will help prevent black spot, while an application of neem oil sprayed every 10 to 15 days during the growing season will aid in preventing black spot.

Cercospora Leaf Spot

• Cercospora leaf spot is a common problem in azaleas and other flowering landscape plants. It produces a mottled discoloration of upper level leaves, usually with a dark purple, almost black or orange color. The culprit behind the disease is the Cercospora kukuchii fungus, which may cause overall heath decline, as well as decreases in flower production. Pruning away infected leaves and applying an antifungal is essential in treating an infected plant.