Black Fungus on Shrubs

Black Spot

• Black spot is a fungal disease that develops on rose bushes and shrubs. Leaves will develop black spots, while the green of the leaves fades to yellow. The fungus can spread from the leaves to the flowers and canes of the shrubs. While it typically does not cause the death of the shrub, it can weaken the plant considerably and make it vulnerable to other infections and diseases. The fungus that causes black spot goes dormant in the winter and will reinfect shrubs in the spring. Fungicides can be used to control the disease and kill the fungus, but all fallen leaves containing black spots and spores must also be removed to keep the shrub from reinfecting itself from the fungus that enters the soil.

Leaf Spot

• Leaf spots can develop on almost all types of shrubs, and while a number of bacteria and contaminants can cause the infection, the culprit is usually a fungus. Spots can be tiny and barely visible or grow to cover nearly the whole leaf. These spots can range in color from red to black, and the spots usually have a reddish border no matter what the center color is. Fungicides can be used to combat leaf spot, but the infection is rarely severe enough to warrant application of fungicide. Many shrubs will suffer from leaf spot for a single season, and the fungus that caused the infection will die during the winter months.

Sooty Mold

• Sooty mold is a condition that develops on the leaves of shrubs that are also infected with aphids or other insects. Insects that excrete honeydew are also excreting a growth medium for fungus. This fungus begins to grow and multiply, forming telltale black spots on the leaves. Several different types of fungus can be responsible for these spots. Sooty mold is best controlled by indirect methods. Determine what kind of insect is excreting the honeydew, and apply appropriate control methods such as pesticides. Once the honeydew is eliminated, the fungus will no longer have a place to grow and thrive.

Prevention

• Black fungus can develop more easily on shrubs that are under stress from other extreme conditions. During times of drought, keep shrubs well watered to keep them healthy and reduce vulnerability. In areas where fungal infections are common, applying a fungicide in the spring or early summer can kill fungus before it has a chance to establish itself. Eliminate insect infestations that can create black fungus problems. Remove any fallen leaves before winter to prevent reinfection the following season.