There are over 175 species of plants in the genus Euonymus, but three species are commonly grown as shrubs in gardens: burning bush (Euonymus alatus), wintercreeper (Euonymus fortunei) and the Japanese spindle tree (Euonymus japonicus). They are grown as accent or hedge plants in U.S. Department of Agriculture hardiness zones 6 through 9, although the burning bush is hardy in zones 4 and 5 because it is winter deciduous.
Usually more prevalent when the growing season (especially spring) is abnormally cool or wet, anthracnose causes brown lesions on leaves that can develop into black spore bodies. When the infestation is severe, considerable leaf drop occurs. According to Clemson University horticulturists, this disease tends to be more harmful to shrubs with variegated foliage.
Bacteria in the soil can infect Euonymus shrubs, causing the roots and lower parts of stems to reveal large, cork-like balls. These galls inhibit the flower of water nutrients between the leafy stems and the roots, ultimately causing slowed growth, leaf wilting and yellowing and, in severe cases, the death of branches. Be mindful that the bacteria remains in the soil for two to three years after an infected Euonymus shrub has been physically removed, so they can infest replacement plants, too.
Manifesting itself on leaves that have a silvery gray and powdery film, this fungal disease can also cause the stunting of newly emerging shoots and leaves. According to Clemson University, powdery mildew is the most common disease found on Euonymus and among the most difficult to control and eradicate completely. Inadequate sunlight, poor air circulation around shrubs and overhead irrigation practices exacerbate problems with powdery mildew. Typically, the leaves look dull and unattractive, but very few leaves end up prematurely dying.
Cercospora Leaf Spot
Rarely deadly to the Euonymus shrub, cercospora leaf spot causes numerous brown spots on foliage, causing the plant to look unattractive. Sometimes the centers of these spots rot and dry out fully to create large holes. Although not detrimental to the plant's health, severe infestations on foliage reduces the plant's ability to make food in its leaves. Over time, this weakens the plant, making it more susceptible to other problems that could kill it.