Commonly known as firethorn, Pyracantha is a genus of about seven species of trees and shrubs growing in U.S. Department of Agriculture plant hardiness zones 6 through 9. Firethorn is susceptible to the fungal diseases sooty mold and powdery mildew. Sooty mold occurs when honeydew-secreting insects -- such as aphids and mites -- infest the firethorn, covering the plant with the sticky substance. Thankfully, sooty mold is rarely a serious problem and requires controlling the honeydew-secreting insects. Powdery mildew, on the other hand, is a more serious fungal disease that causes infected plants to experience distorted and wilted, dropped leaves and stunted growth. Sooty mold leaves a black soot-like growth covering the foliage, buds and stems of the firethorn; powdery mildew creates a white cottony growth on the plant. Once you have identified the fungal disease, treat it accordingly and take the necessary preventive measures to keep the problem from returning.
Pour 1 gallon of water in a clean handheld garden sprayer. Add 1 ounce of neem oil concentrate and mix for several seconds.
Spray the firethorn with the neem oil, making sure to coat the undersides and tops of the leaves. Shake the handheld garden sprayer periodically while applying the pesticide.
Repeat the treatment with a fresh solution once every seven to 14 days until the honey-secreting insects are controlled.
Spray the firethorn plant with a hose to wash off the sooty mold.
Pour 2 tablespoons of neem oil concentrate and 1 gallon of water in a garden sprayer. Shake the sprayer for several seconds until the neem oil and water are well mixed.
Spray the firethorn with the solution thoroughly, making sure to cover the tops and undersides of the leaves.
Reapply the fungicide every seven to 14 days, as needed, with a fresh mixture.