The golden euonymus, or aureo-marginata, is a cultivar of Euonymus japonicus. Though this evergreen shrub can be an attractive addition to your yard or garden hedge, it's susceptible to certain fungi diseases, bacterium and pest infestations. Due to a tendency to be decimated by mildew, the plant even received the dubious honour of "Awfulest of the Awful" in a 2009 "Southern Living" magazine article entitled "Five Awful Plants for the Front of Your House." Fortunately, with treatment most golden euonymus can be restored to their golden-tipped beauty.
The fungus Oidium euonymi-japonici, also known as powdery mildew, loves to infect golden euonymus. Powdery mildew is both the most common euonymus disease and the hardest to control, according to the Clemson University Cooperative Extension. Powdery mildew is characterised by greyish-white, flat growths on the tops of leaves. Affected leaves tend to turn yellow, curl, scar and sometimes drop. To treat, prune and destroy affected branches and leaves, then apply systemic fungicide. Prevent powdery mildew by planting golden euonymus in full sun, giving each plant adequate space, and avoiding overhead watering.
Crown gall is characterised by round hard growths, or galls, up to a few inches in diameter that appear on the plant base, stems and roots. Caused by an infection of Agrobacterium tumefacien, a soil bacteria, galls prevent water and nutrients from circulating through the plant. Infected plants turn yellow and weak and grow slowly. Treat crown gall by pruning affected areas and destroying badly damaged plants. Sterilise your shears with alcohol after each cut, as the disease is contagious and spreads through instruments, plants and soil. The bacteria can remain in the soil near affected plants for up to three years.
Cercospora Leaf Spot
Cercospora leaf spot is caused by two fungi, Cercospora detructiva and Cercospora euonym. While Cercospora leaf spot does not kill plants, it causes unattractive brown blemishes on leaves. Spots can be up to ½-inch wide and join with other spots to cover entire leaves. As spots grow, they turn grey and sprout small black fruits. To treat Cercospora leaf spot, rake and destroy any fallen leaves around the plants. The Clemson University Cooperative Extension recommends applying a systemic fungicide that contains thiophanate-methyl.
If the leaves or twigs of a golden euonymus have small, brown spots with light centres, anthracnose may be the culprit. The Colletotrichum fungus causes anthracnose, and, if left untreated, causes leaf cracks to develop, which can result in heavy leaf drop or even defoliation. The disease tends to be worse in cool wet weather and in variegated euonymus varieties. To treat anthracnose, prune affected areas and rake and destroy all fallen leaves and twigs. Copper fungicide sprays and chlorothalonil help prevent the disease from reoccurring.
If left untreated, the appropriately named "scab" causes spots on leaf surfaces that can disfigure golden euonymus plants. Sphaceloma or Elsinoe euonymi-japonici fungi cause scab. Spots appear to be "small, greyish white with a raised orange-cinnamon, waxy-appearing margin and, in the larger spots, a raised, dark centre," according to the Clemson University Cooperative Extension. Treat scab by destroying fallen leaves and applying a fungicide containing thiophanate-methyl.