Viburnum and Insects
Viburnum, a member of the honeysuckle family, grows as a shrub or small tree. Some viburnums produce fragrant flowers and brilliantly colored fruits, while others are grown for their beautiful foliage. Depending on the type of viburnum, the plant may be evergreen or deciduous. Viburnums are easy to grow in various types of soil and climates, but can fall prey to a wide variety of insect pests.
Sometimes called black fly or black bean aphid, Aphis fabae has piercing, sucking mouthparts through which it feeds on the viburnum plant's juices. Bean aphids are dark green or blackish, and adults may be winged or wingless. Like all aphids, bean aphid is pear-shaped and has two protrusions at its rear end, called cornicles. Although a small population of bean aphids causes little damage, if the aphids form colonies, their feeding can cause stunted, deformed growth and turn the viburnum's leaves yellow. Aphids exude a sticky substance called honeydew that attracts ants and often leads to sooty mold. Use a hard spray from the garden hose to knock bean aphids off the viburnum plant. For heavier infestations, spray the plant with neem or horticultural oil or insecticidal soap to smother the aphids. Introduce natural enemies such as parasitic wasps or lady beetles to the area to kill the aphids. Eliminate sowthistle and other weeds where aphids can hide.
Black Vine Weevil
The wingless adult black vine weevil (Otiorhynchus sulcatus) feeds on the viburnum's leaves, causing the foliage to appear ragged. The larvae feed on the viburnum's roots, which can weaken and even kill the plants. Adults are 3/8 inch long, black or brownish. The 1/2-inch-long larvae are C-shaped, white, with brownish heads. Place a white cloth on the ground under the viburnum and shake the branches to dislodge the weevils. Collect the insects and drop them in a pail of soapy water to kill them. Apply sticky tape to the stems in early spring to keep the beetles off the viburnum. Introduce parasitic nematodes to kill the weevils. In severe cases, select a commercially available pesticide labeled to control black vine weevils and apply according to label directions.
Spider mites are nearly microscopic pests that spin webs and live in colonies, becoming most numerous in summer. Like aphids, spider mites suck plant juices from the viburnum, causing stippling, yellowing and leaf drop. Large colonies stretch webs over leaves, fruit and twigs. Water-stressed viburnum are more prone to spider mite infestations than healthy plants. Predatory mites, sixspotted thrips and the spider mite destroyer lady beetle provide natural control of spider mites. Spray the viburnum with the garden hose. Insecticidal soap or a pesticide formulated to treat spider mite infestations can help control the insects. Be sure the pesticide lists spider mites, as some pesticides actually increase spider mite reproduction.
Greenhouse thrips, Heliothrips haemorrhoidalis (Bouché), feed on flower pollen and on the undersides of the viburnum's leaves, often causing the leaves to fade significantly. These insects are less than 1/20 of an inch long and have a black body with pale, fringed wings. They leave black dots of excrement on the leaves while they're feeding. Parasitic wasps may help control greenhouse thrips. Treat a heavy infestation with insecticides containing acephate, carbaryl, imidacloprid, malathion, permethrin, potassium salts, pyrethrins or spinosad. Follow label directions carefully.
Armored scales such as the oystershell build protective, waxy coverings over their shield-shaped bodies. The insects produce damage similar to aphids. Oystershell scale insect colonies may appear like a whitish or grayish crust on the viburnum's stems or branches. Unlike aphids, oystershell scale's saliva is toxic and can cause the viburnum to decline. Prune out heavily infested areas and destroy the cuttings. Neem oil, horticultural oil or pesticides containing pyrethrins, acephate or malathion may reduce populations of armored scale. Neem and horticultural oils kill only the insects present when sprayed, allowing beneficial predator insects to visit later.
Audrey Lynn has been a journalist and writer since 1974. She edited a weekly home-and-garden tabloid for her hometown newspaper and has regularly contributed to weekly and daily newspapers, as well as "Law and Order" magazine. A Hambidge Fellow, Lynn studied English at Columbus State University.