Viburnum Awabuki Pests & Diseases
Viburnum odoratissimum var. awabuki is an evergreen plant with a spreading habit. It grows 15 to 20 feet tall and wide, and it can be pruned as a tree. The small fragrant flowers are followed by bright red berries that turn black. Viburnum awabuki is hardy in zones 9 to 11 and grows best in well-drained soil in full sun. Plants that are in the shade or located too close together are more prone to diseases. Most diseases and pests on Viburnum awabuki do not cause serious damage, although a few diseases can kill infected plants.
Damage caused by pests that feed on the foliage of Viburnum awabuki affects the appearance of the plant but normally does not harm it. Curled or rolled leaves are symptoms of aphid or thrip infestations. Thrips also cause purplish-red spots on the underside of the leaves, where they scrape the cells and suck the sap. Spider mites are active in the cool weather of spring and fall when they pierce the foliage and feed on the sap. The leaves turn grayish-brown, the leaf tissue collapses and the foliage drops prematurely.
Adult root weevils only feed on the leaves, but the larvae chew on the roots. When the roots are girdled, the foliage turns pale green or yellow, the plant declines and it eventually dies. You can wash aphids off the foliage with a strong spray of water. Insecticides approved for viburnums can be used at the rate and schedule recommended by the manufacturer to control or eliminate thrips, spider mites and root weevils.
Bacteria, fungi or algae can cause leaf spots on Viburnum awabuki. Bacterial leaf spots begin as water-soaked areas that develop into sunken brown areas. Infected leaves should be removed and destroyed to prevent the spread of the disease. Fungal leaf spots occur during warm moist summer months. Grayish to reddish brown, angular or irregular patches usually appear on the older foliage first. Cercospora, Phoma and Phyllsticta are common fungal agents on viburnums. Remove and destroy infected foliage, and use a fungicide for viburnums following the manufacturer’s directions. Algal leaf spots, caused by Cephaleuros virescens, grow in cool moist conditions. The small pale green spots turn light or reddish brown with age. Use a copper-based fungicide according to the manufacturer’s instructions, and remove and destroy infected foliage.
The fungus Botryosphaeria infects stressed plants and causes cankers, limb dieback, and rapid browning and wilting of foliage. Prune and destroy infected plant parts, and apply a fungicide for viburnums to the pruning cuts following the manufacturer’s instructions. Erysiphe sparsa fungus causes powdery mildew during humid weather with warm days and cool nights. The white to grayish dusty growth is usually worse on young leaves and shoots. Another fungus, Plasmorpara vibumi, causes downy mildew during cool or warm wet weather. Light green spots develop on the upper surfaces of infected leaves, and grayish fungal masses grow on the underside. Both can be treated with a fungicide for viburnums according to the manufacturer’s directions.
Bacterial crown galls grow on the lower stems of Viburnum awabuki. Remove and destroy the affected plant, and do not replant the area with a viburnum. Armillaria root rot is also called mushroom root rot or shoestring root rot. White feltlike mats and black strands of fungal growth develop under the bark on the crown and upper roots. The affected plant has yellow leaves and stunted growth, and it eventually dies. Remove the plant, its roots and surrounding soil; do not replant the infected area.