Although euonymus (Euonymus spp.) shrubs are adaptable plants and simple to care for, they are susceptible to a range of fungal and bacterial diseases that affect their appearance and growth. Hardy from U.S. Department of Agriculture plant hardiness zones 4 through 9, euonymus may be evergreen or deciduous, and are popular choices for hedges, borders and screens. Knowing the key characteristics of euonymus diseases can help you identify problems and successfully treat afflicted shrubs.
The most common disease to afflict euonymus comes in fungal form. Hard-to-control powdery mildew is distinguished by flat, gray to white growth that "powders" the upper leaves of your plant. If severe, it can scar and wither young growth. To prevent powdery mildew, avoid overhead watering and give the shrub plenty of sunlight and air. If mildew strikes, spray all the shrub's leaves with a ready-to-use, copper-based fungicide to stop the spread. Spray until all surfaces are wet. The fungicide will protect new leaves, but does not get rid of powdery mildew from already infected parts of the plant. Repeat the application every seven days.
Anthracnose is another type fungus that affects the euonymus shrub. This leaf spot fungus, caused by a number of differrent fungal species, forms brown spots with gray centers on leaves and twigs. The disease can result in severe defoliation of your shrub if left untreated. Prune and clean up diseased leaves and branches, using sharp bypass pruners sterilized with household disinfectant before and after each cut. For severe cases, spray a copper fungicide in the same manner used for mildew.
Cercospora Leaf Spot
Another leaf spot fungus Cercospora detructiva causes distinctive spots to appear on healthy euonymus leaves. Cercospora leaf spot is distinguishable by the presence of varying sizes of brown spots with the larger spots bearing a grayish center. While not life threatening, you can spray Cercospora leaf spot with a copper fungicide to keep the disease in check, as you would use for treating powdery mildew. As with any disease, clean up fallen infected leaves to prevent further spread.
Some euonymus species are afflicted by scab, from the fungus Sphaceloma or Elsinoe euonymi-japonici. Scab can disfigure the euonymus by causing small gray spots encircled by orange margins to grow on leaves and stems. If left alone, the spots grow larger, sometimes merging together. A copper-based fungicide like that for powdery mildew and leaf spot can prevent and control scab.
The bacterium Agrobacterium tumefaciens inhabits soil and causes crown gall to form at the base of the plant. Identify crown gall by the presence of large, knotted galls growing on the stems and roots of your euonymus shrub. Galls harm the water and nutrient flow to the rest of the plant, causing leaves to yellow and overall growth to slow. Crown gall is spread by infected soil and has no cure. However, your euonymus shrub can still live for several years even while infected. Prune off unsightly growth, always sterilizing your pruning tools.