Sweet Viburnum Is Dying

Sweet viburnum (Viburnum odoratissimum) is a large shrub to small tree native to west and southern coastal regions of the United States. This broad-leaf evergreen reaches heights of 10 to 30 feet with a symmetrical rounded formation and showy clusters of creamy white springtime flowers. Landscapers use sweet viburnum as a hedge and screen plant. Many issues including pests, diseases and improper care, can result in the death of part or all of this ornamental plant.

Maintaining a healthy plant boosts sweet viburnums defense against problems. Plants that lack the fulfillment of their basic requirements suffer from stress, which attracts trouble from unwanted pests and diseases. Sweet viburnum is a versatile plant that thrives in well-draining soils, with full to partial sun or partial shade. This drought-tolerant species likes clay, loam and sandy soils. Sweet viburnum requires regular watering; however, avoid overwatering by allowing the soil to dry between applications. Overwatering a plant leads to attacks by pests and diseases.

Sweet viburnum is a pest-resistant variety; however, when unhealthy or damaged plants become weak, many pests invade. Flower thrips (Frankliniella tritici) are narrow, dark-bodied insects with ruffled wings that feed by scraping the cells off viburnum leaves and flowers. These pests cause premature leaf drop and death to the plants flowers. Southern red mites (Oligonychus illicis) have piercing mouthpieces with red bodies; these arachnids suck sap from the foliage of the plant, resulting in premature leaf drop. Oystershell scales (Lepidosaphes ulmi) are armored brown and gray pests that attach themselves to the bark of viburnum to lay eggs; an infestation creates branch dieback, which eventually kills the plant.

Several diseases affect sweet viburnum, causing damage and possible death to the plant. Armillaria root rot, caused by the fungus Armillaria mellea, infects many parts of the plant, resulting in death. Symptoms include rotted roots, stunted appearance, yellowing and dropping leaves. Prevention through proper plant care is the only means of treating armillaria root rot; once infected, the plant dies. Botryosphaeria dieback and canker is a debilitating disease caused by Botryosphaeria species plant pathogens. This disease attacks stressed viburnums by creating cankers, which girdle bark, resulting in dieback. Foliage becomes discolored and wilted because of the disruption of the flow of water throughout the plant; some branches with cankers do not grow leaves the next spring. Foliage diseases, like fungal leaf spot, algal leaf spot, downy mildew and powdery mildew, create an unsightly appearance but do not result in death.

Flower thrips and southern red mites have enemies that prey on them. Natural predators of flower thrips and southern red mites include ladybugs, pirate bugs, lacewings and damsel bugs. Predatory mites Amblyseius mackenziei and Amblyseius cucumeris consume flower thrips, and predatory mites Phytoseiulus persimilis and Amblyseius californicus rid plants of southern red mites. Hand removal of Oystershell scales only works when a light infestation occurs; a heavier presence calls for applications of horticultural oil in early spring. Pruning cankers from sweet viburnum is an effective treatment for removing the infected spots.