Leaves Curled, Discolored due to Aphids
Aphids, also called "plant lice," attack tender branches and flower clusters. The pests are spindly-legged, pear-shaped insects little bigger than the head of a pin. They suck sap from leaves and stems, causing the foliage to curl, pucker, and turn yellow, while reducing the plant's vigor. Ants, attracted by the aphids' honeydew secretions, wander over the plants and protect the aphids from natural predators. Check leaf undersides for small groups of aphids. For light infestations, spray leaf undersides vigorously with water three times, once every other day, in the early morning. Eliminate nearby ant nests if possible. Use insecticidal soap every 2 to 3 days for heavier infestations. As a last resort, use pyrethrum spray.
For more information see file on Controlling Aphids.
Foliage And Flowers Skeletonized means Asiatic Garden Beetles
Asiatic garden beetles skeletonize new leaves, flowers, roots and the bases of young stems. They are most active at night. The larvae (grubs), which are grayish, 3/4 inch long, and bent in a C-shape like Japanese beetle grubs, live underground and eat the roots. The adults are velvety chestnut-brown, nearly 1/2 inch long, resembling Japanese beetles. They lay their eggs in the soil at the base of the plants. Immediate control steps include handpicking and applying beneficial nematodes to the soil. For long-term control, apply milky spore disease (Bacillus popillae) powder to the soil. In the spring, carefully cultivate the soil around the shrubs to expose insect eggs, larvae and pupae to the weather and to birds. Avoid damaging the roots. For more information see the file on Controlling Asiatic Garden Beetle.
Holes In Twigs, Exuding Sawdust indicates Dogwood Twig Borers
Borers enter stem tips and bore out some of the twigs soon after blooming time. As they grow, these larvae bore into the main stems, pushing out fine sawdust as they go. The borers' activity leaves ugly scars and sometimes kills large branches. Dogwood twig borer grubs are dull yellow, 3/4 inch long. They winter over in the twigs of the viburnum. Adult beetles appear in the spring. In June, crush any eggs that you can find. An effective but tedious remedy is to shove a wire into each borer hole to crush or remove the borer. Try injecting nicotine paste into borer holes. The most complete control is to prune and burn affected stems if you can avoid deforming the shrub.
For more information see file on Controlling Borers.
Plant Stunted, Leaves Yellowed; Root Lesions because of Nematodes
Plants infested with nematodes look sickly, wilted, and stunted. They develop yellowed or bronzed foliage, decline slowly and eventually die. Their root systems are poorly developed, even partially decayed. Southern root knot nematodes attack Viburnums. These are slender, unsegmented roundworms that live in the soil. They're less than 1/-inch long, invisible to the unaided eye. They have piercing-sucking mouthparts. Add lots of compost (especially decomposed leaves) to the soil around the Viburnum plants to encourage beneficial fungi that attack nematodes. Liquid fish emulsion, poured into the soil as a drench, is toxic or repellent to nematodes. Try inter-planting French marigolds among the Viburnum plants; their root exudations repel or kill nematodes.
Leaves And Branches Encrusted With Small Bumps caused by Scale Insects
The first sign of a scale attack is often discoloration of upper leaf surfaces, followed by leaf drop, reduced growth, and stunted shrubs. Aptly named, scale insects are covered by hard, rounded waxy shells, which are colored white, yellow, or brown to black. They are about 1/10 to 2/5 inch in diameter. Heavy scale infestations may kill viburnums. Some species of scale insects excrete honeydew, which coats foliage and encourages ants and the growth of sooty mold, a gray to black coating on the leaves and stems. Early on, you can scrape scale off plant surfaces with your fingernail or a cotton swab dipped in rubbing alcohol. Spray more heavily infested plants with a mixture of alcohol and insecticidal soap every three days for two weeks. Mix 1 cup of rubbing alcohol and 1 tablespoon of insecticidal soap concentrate in 1 quart water. If your insecticidal soap is already mixed with water, add 1 tablespoon of alcohol to a pint of the diluted soap spray.
For more information see file on Controlling Scale
Leaves Have Silvery Pallor due to Thrips
Thrips damage results from these insects' habit of rasping at plant cells and sucking sap from the injury. Viburnum leaf surfaces are flecked and whitened; leaf tips whither, curl and die. Leaf undersides are spotted with tiny black specks of excrement. Adult thrips are tiny, slender insects, 1/25 inch long. They are variously colored--pale yellowish, black or brown. They have 4 long, narrow wings fringed with long hairs and very short legs. Their larvae are usually wingless. Since thrips burrow deeply between flower petals, early identification and control are necessary. Set out yellow sticky traps about 4 weeks after last frost as early warning devices. As soon as you spot thrips on the trap, apply a spray of insecticidal soap every 3 days for 2 weeks. Commercially available predatory mites, lacewings, ladybugs and beneficial nematodes are effective backups to the soap spray. Thrips prefer a dry environment, so make sure plants are adequately misted or watered. For more information see the file on Controlling Thrips
More Problems
Sunken Spots on Leaves means Anthracnose
This fungus disease forms distinct lesions on leaves, which appear as moist, sunken spots with fruiting bodies in the center. The spots may run together, resembling a blotch. The dead areas follow the veins or stop at larger veins. Sometimes terminal shoots die down to several inches below the buds. Gather and destroy diseased leaves when they fall and prune away diseased branches. Maintain plant vigor by feeding and watering well, especially during droughts. Spray with a copper fungicide such as Bordeaux mixture.
For more information see file on Controlling Fungal Disease
Buds and Flowers Spotted, Leaves Blotched indicates Blight
When infected by this fungus disease, flowers become spotted, spots enlarge into blotches, and the flowers deteriorate. Leaves develop grayish brown decayed patches. The fungus attacks dense flower clusters during wet weather. Spray plants with copper fungicide when symptoms first appear and then every 10 days in wet seasons. Avoid overhead watering. Prune to increase air circulation around plants, taking care to sterilize pruning tools by dipping them in household bleach to prevent the disease from spreading.
For more information see file on Controlling Fungal Disease
Tumor-like Swellings on Stems because of Crown Galls
A bacterium infects viburnum shrubs through wounds. It stimulates cells to form tumor-like swellings (galls) with irregular rough surfaces along the stems. Serious infection causes branches to die back. Prune out and discard all branches bearing galls.
Dead Blotches on Leaves caused by Leaf Spot
Various leaf spot fungi cause yellow, brown or black dead blotches on the leaves that frequently run together. Heavily infected leaves turn yellow or brown and fall prematurely. Cool, moist weather favors these diseases, especially when new leaves are developing. Shake out all fallen and diseased leaves from the center of the viburnum shrubs and destroy them. Remove all dead branches in the center of specimen plants or hedges to allow better aeration. Mulching helps prevent the disease from splashing up from the ground and infecting plants. Spray at weekly to 10-day intervals with sulfur or Bordeaux mixture or other copper fungicide, particularly in rainy weather. Cut down and discard seriously infected shrubs together with the soil ball.
(Note: Sulfur-based fungicides may harm some viburnum varieties. Test the sensitivity of your particular Viburnum by treating one branch and watching it for 3 days to see if any discoloration occurs. If the branch and leaves seem to be unaffected after that time, you should be able to use sulfur on the plant.)
For more information see file on Controlling Fungal Disease
Leaves Covered With White Powder due to Powdery Mildew
Powdery mildew, caused by a fungus, develops mostly on the upper surfaces of viburnum leaves and appears as whitish blotches. In late summer, bushes in shady spots may be badly infected. If the disease is serious, spray thoroughly with wettable sulfur once or twice at weekly intervals, starting as soon as the whitish coating of the fungus is visible. Collect and discard all plant refuse in the fall.
For more information see file on Controlling Fungal Disease
Rust Colored Spots on Leaves means Rust
Rust infections usually appear as numerous rust-colored, orange, yellow or white, powdery, raised localized spots. Infected leaves wilt and wither and the plants may be stunted. Rusts are caused by various fungi that attack leaves and stems and sometimes flowers. Remove infected leaves as soon as possible. Remove and destroy diseased plants and all debris before growth starts in the spring.
For more information see file on Controlling Fungal Disease
Foliage Burned indicates Dog Urine
Urination by dogs may discolor foliage and even kill branches. Spraying foliage with an anti transpirant gives some protection. Screen the plants or spray with an aerosol pet repellant. For more information see the file on Dealing With Dogs and Cats
Bark of Trunk and Roots Gnawed because of Rodent Injury
Small rodents gnaw bark off trunks, causing injury that allows disease organisms to invade. Rake mulch away from tree bases during the winter; keep the area clear of weeds and grass; and wrap the trunk base with a guard of 1/4-inch hardware cloth.
For more information see files on Dealing With Mice and Dealing With Rabbits and Dealing With Voles
