Fungus on Evergreen Shrubs

Types of Fungus

• Sooty mold is a common fungus on both evergreen and deciduous shrubs. It looks like a black dust on the shrub's leaves and twigs. Sooty mold is attracted and nourished by honeydew, produced by several types of insects and other pests. If too much mold builds up on the plant, it may interfere with photosynthesis. Other fungi that attack evergreen shrubs include stem rust, which favors the barberry shrub, and phytophthora root rot, which afflicts one of the most commonly grown shrubs for hedges, boxwood.

Symptoms

• Determining what ails your shrub is challenging. Many fungal diseases mimic other problems, such as pest infestations or herbicide damage. Sooty mold is easy to diagnose with its black, powdery evidence left on the shrub's foliage. However, a boxwood with yellow leaves may be suffering from lack of water, herbicide drift or root rot. Leaf spots are typically an indication of a fungal infection as are symptoms that appear on only one side of the shrub.

Treatment

• The best course of action to take when you notice a problem with your shrub is to check first for an insect infestation. Sucking pests, such as aphids, extract juices from the shrub, causing yellowing and leaf spots. When dealing with sooty mold, getting rid of the aphids keeps the fungus from growing. If there is no pest problem and the shrub's cultural requirements are being met, suspect a fungal infection. Purchase commercial fungicides listed to manage the specific pathogen that is infecting the shrub. If you are unable to determine the pathogen, take an infected leaf or stem to the county’s cooperative extension office for diagnoses.

Prevention

• The causes of fungal infections vary by the pathogen’s species. Some require moisture for a specific time to reproduce. Others, such as powdery mildew, thrive in a dryer environment. Pruning the shrub’s interior allows air to better circulate and cuts down on many fungal infections. Avoid watering the shrub overhead, such as with sprinklers. Watering at soil level keeps the foliage dry and watering slowly avoids splashing soil onto the plant. If the shrub is planted in the lawn, use care when mowing around it. Some fungi use wounds to gain entry into shrubs. Avoid applying nitrogen fertilizer late in the season. This prevents excess new growth, which some fungal pathogens thrive on during cooler fall weather.