Euonymus Diseases & Insect Pests

Diseases

Powdery Mildew: Powdery mildew is the most common and possibly the most difficult disease to control on euonymus. It is caused by the fungus Oidium euonymi-japonici. Symptoms consist of a flat, white to gray growth primarily on the upper surfaces of the leaves, which can be rubbed off easily. Leaves may yellow slightly and drop, but heavy leaf drop is not a characteristic symptom. On young shoots leaves can become curled and scarred if infection is severe.

Prevention & Treatment: Prune and destroy heavily diseased branches. Remove and destroy fallen leaves. Plant in a sunny area, do not crowd plants, and avoid overhead watering. Chemical applications should begin before new foliage is infected. Fungicides will protect foliage from infection (by killing the mildew spores as they germinate) but will not remove the dense, white fungal growth from infected leaves. Myclobutanil (Spectracide Immunox), propiconazole (Ferti-Lome Liquid Sytemic Fungicide or Bonide Infuse Fungicide), thiophanate-methyl (Ferti-lome Halt Fungicide, Green Light Systemic Fungicide, Cleary's 3336), and triadimefon (Green Light Fung-Away) have systemic properties and can be sprayed less often than sulfur or copper fungicides (Camelot Fungicide/ Bactericide). When powdery mildew persists and sprays are repeated, it is recommended to rotate fungicides to decrease the chance of fungi developing resistance. Read and follow all directions on the label.

Crown Gall: Crown gall is caused by the soil-inhabiting bacterium Agrobacterium tumefaciens. Large, corky galls up to several inches in diameter appear at the base of the plant and on the stems and roots. The galls are rounded, with a rough, irregular surface. Plants with numerous galls are weak, growth is slowed and leaves turn yellow. Branches may die back. The galls disrupt the flow of water and nutrients to the top of the plant.

Corky textured crown gall on winter creeper euonymus.
Division of Plant Industry Archive,
Floridia Department of Agriculture and Consumer Services, www.forestryimages.org

Prevention & Treatment: The bacteria are spread by infested soil, transplants and contaminated tools. Even though infected plants cannot be cured, they usually survive for many years. To improve the appearance of the plant, prune out and destroy affected stems below the galled area. Sterilize pruning shears after each cut with rubbing alcohol. Destroy severely infected shrubs. The bacteria will remain in the soil for two to three years. If you wish to replace the shrub, plant only resistant species, such as barberry, boxwood, holly, mountain laurel and elderberry.

Cercospora Leaf Spot: The fungi Cercospora detructiva and C. euonymi cause irregularly shaped brown spots on the leaves. The spots vary in size from pinpoints to half an inch across. They often merge to cover whole leaves. The centers of large spots become grayish tan and the causal fungus produces tiny, black fruiting bodies on the upper surface of the spots.

Cercospora leaf spot on Japanese euonymus.
Division of Plant Industry Archive,
Floridia Department of Agriculture and Consumer Services, www.forestryimages.org

Prevention & Treatment: Leaf spot is fairly common but rarely life-threatening to the plant. Rake up and destroy all fallen leaves. Spray diseased plants with thiophanate-methyl (see brands under powdery mildew control). Read and follow all directions on the label.

Anthracnose: Anthracnose is caused by the fungus Colletotrichum species. Symptoms consist of small, brownish spots with light-colored centers on the leaves and twigs. Tiny cracks in the leaf spots indicate fruiting structures of the fungus. Considerable defoliation can result. The disease is a problem during cool, wet springs. Variegated varieties are more susceptible.

Prevention & Treatment: Rake up and destroy leaves and twigs from infected plants. On smaller plants, prune off and destroy all infected growth at the first sign of infection. Severe outbreaks may be prevented with periodic applications of chlorothalonil (Bonide Fung-onil Multi-Purpose Fungicide, Ortho Garden Disease Control, Ferti-Lome Liquid Fungicide, or Daconil 2787) or copper fungicide sprays. Read and follow all directions on the label.

Scab: This disease, caused by the fungus Sphaceloma or Elsinoe euonymi-japonici, disfigures Japanese euonymus. Spots develop on both surfaces of leaves but are most common on the upper one. The spots are very small, grayish white with a raised orange-cinnamon, waxy-appearing margin and, in the larger spots, a raised, dark center. When they are numerous, the spots may merge together. The centers of the leaf spots sometimes fall out. On the stems, spots are similar to those on the leaves, but they are often darker in color and more likely to merge together.

Prevention & Treatment: Rake up and destroy all fallen leaves and spray with thiophanate-methyl (see brands under powdery mildew control). Read and follow all directions on the label.

Insect Pests

Several species of scale are pests on euonymus. Scales are unusual insects in appearance. They are small and immobile, with no visible legs. Scales vary in appearance depending on age, sex and species. They feed on sap by piercing the leaf or stem with their mouthparts and sucking.

Numerous white male euonymus scales may almost cover the underside of leaves.
The female are larger and darker.
Karen Russ, ©2009HGIC, Clemson Extension

Euonymus Scale (Unaspis euonymi): This is the most common and most serious pest found on euonymus. The protective armor covering of an adult female euonymus scale is dark, oyster-shaped and about 1/16-inch in length. Adult males are very small, winged insects that leave their narrow, white armored covering for mating. The eggs laid by the female are yellow and found beneath the female's covering. When the eggs hatch, the crawlers (immature forms) move around before forming their own protective covering. Males typically outnumber females. With a heavy infestation, clusters of white males can be easily seen on leaves and stems. Initial symptoms of euonymus scale infestation are yellow spots on leaves. With a heavy infestation, branches and possibly the entire plant may die.

Yellow spots on top surface of leaves are and early symptom of euonymus scale infestation.
Note scales along leaf veins.
Karen Russ, ©2009HGIC, Clemson Extension

Prevention & Control: The following Euonymus species are resistant to euonymus scale: E. alatus 'Compactus' and E. fortunei 'Acutus.' Consider using these in new plantings. Euonymus scale is difficult to control. With light infestations, scale can be scraped off by hand and destroyed. Pruning out heavily infested branches is helpful. Avoid using insecticides unless the plant is very valuable and in serious danger from scale. Insecticides will often kill the naturally occurring enemies of scale.

Adult scales are relatively protected from insecticides by their waxy covering. Their immature forms, called crawlers, are susceptible, however. Horticultural oil (Bonide All Season Spray Oil, Ferti-lome Scalecide, Green Light Horticultural Oil Spray, or Ortho Volck Oil Spray) can be used as a dormant spray before new growth begins in the spring. It kills many adults and eggs by smothering them. Spray again when crawlers are present in the spring.

Monitor the crawler emergence with sticky cards, double-faced tape wrapped around a branch, or by putting an infested shoot or leaf into a baggie and watching for crawler movement. Crawler activity often coincides with the flush of new plant growth in the spring. However, some scale species may have overlapping generations with an extended crawler emergence period, such as along the coast.

If insecticides are necessary, the following are effective against crawlers: acephate (Ortho Japanese Beetle Killer), malathion (Ferti-lome Mal-A-Cide or Hi-Yield Malathion Insect Spray), cyfluthrin (Bayer Advanced Garden Power Force Multi-Insect Killer), and carbaryl (Sevin 50WP or Ferti-lome Carbaryl Spray). Make sure that crawlers are present before using them. Apply three sprays at 10-day intervals. As with all pesticides, read and follow all label instructions and precautions.

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