Shrub Dies Suddenly means Improper Cultivation
Daphne shrubs in general and fragrant daphnes in particular are extremely sensitive to their surroundings. They have the disconcerting tendency to up and die suddenly for no apparent reason. Often the cause is a subtle change in their environment--too much water or fertilizer, exposure to rapid temperature change, the proximity of another plant. Usually the cause is not known.
Leaves Curled, Discolored due to Aphids
Aphids are spindly-legged, pear-shaped insects little bigger than the head of a pin. Also called "plant lice," they attack tender branches and flower clusters on shrubs. These pests suck sap from leaves and stems, causing the foliage to curl, pucker, and turn yellow, while reducing the plant's vigor. Sometimes ants, attracted by the aphids' honeydew secretions, wander over the plants and protect the aphids from natural predators. Check under the daphne leaves for small groups of aphids.
To dislodge light infestations, spray the undersides of the leaves vigorously with water three times, once every other day, in the early morning. Spray insecticidal soap every 2 to 3 days for heavier infestations. As a last resort, use pyrethrum spray, spraying it directly on the aphids. Take care to use pyrethrum late in the day to minimize killing honeybees and other beneficial insects nearby. Destroy nearby ant nests by breaking them open and pouring boiling water on them. On evergreen shrubs like fragrant daphne, apply a "light" horticultural oil spray on the foliage in the early spring to suffocate over wintering eggs.
For more information see file on Controlling Aphids.
Cottony Masses on Plant Parts indicates Mealybugs
Mealybugs are 1/5 to 1/3 inch long, with oval, flattened bodies. They are covered with white waxy powder and adorned with short, soft spines around their edges. These insects sometimes gather in cottony white masses on daphne roots, stems, branches and leaves, sucking sap and reducing the plant's vigor. Infested daphne leaves look yellowish; severely infested plants are unsightly, do not grow well, and may die. Honeydew secretions from the insects' feeding encourage mold growth on the shrub foliage and attract ants.
Control mealybugs by spraying them with an alcohol-insecticidal soap spray every 2 to 3 days until the pests disappear. Mix 1 cup of rubbing alcohol and with one pint of insecticidal soap mix. To kill over wintering mealybug eggs spray daphne foliage and stems with a light horticultural oil in March or April, just before new growth starts.
Leaves And Branches Encrusted With Small Bumps because of Scale Insects
Scale insects are covered by hard, rounded waxy shells, which may be colored white, yellow, or brown to black. These small bumps are found ranged along stems and twigs of infested daphnes. They are about 1/10 to 2/5 inch in diameter. The first sign of a scale attack is often discoloration of the tops of the leaves, followed by leaf drop, reduced growth, and stunted shrubs. 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. Heavy scale infestations may kill daphnes.
Handle mild scale infestations by simply scraping the telltale bumps off plant surfaces with a fingernail, or a cotton swab dipped in rubbing alcohol. Heavy infestations require spraying. Use a mixture of alcohol and insecticidal soap every 3 days for 2 weeks. Mix 1 tablespoon of alcohol in a pint of ready-to-use commercial soap spray. Light horticultural oil sprayed on dormant plants in late winter or early spring will smother over wintering scale. Apply insecticides when the young larvae (or "crawlers") have hatched and before they start forming their new scales.
For more information see file on Controlling Scale.
Sudden Wilting; Death due to Southern Blight
This fungal disease of many types of woody plants thrives in hot weather and acidic soil. Although it is most common in the southeast, it appears sporadically in the north. It tends to attack young shrubs that have not yet developed corky bark on their stems. The infection starts near the soil line, appearing as a dark, discolored area covered by a webbing of fungal threads, eventually girdling the stem. The disease can kill a daphne shrub in less than 1 month. Because the fungus lives in soil and plant debris, it is important to collect and discard in the trash all weeds and plant parts near infected shrubs. Dig up and get rid of soil near sick plants. In the North kill this blight fungus by pulling off the mulch around the daphne shrub to expose the soil to winter frost. Researchers are developing an antagonistic fungus that can some day be used to control this disease.
For more information see file on Controlling Fungal Disease
Brown Spots On Leaves means Leaf Spot
Some types of fungi cause thick brown spots to develop on both sides of daphne leaves. These leaves then turn yellow and wilt, eventually dying. Treat infected shrubs by promptly picking off all leaves and twigs that show symptoms and discarding them in the trash. Spray affected shrubs with copper fungicide according to directions on the package.
For more information see file on Controlling Fungal Disease.
Branch Tips Turn Brown; Die Back due to Twig Blight
A blight disease caused by a fungus occurs on daphne through the Northeast out to the Pacific Northwest. It causes branch tips to turn brown then die back until the entire branch, or even the entire shrub, is killed. Shrubs over 5 years old are usually not seriously affected. In late winter, prune and burn affected twigs and branches.
Spray plants with copper fungicide or lime sulfur fungicide when symptoms first appear and then every 10 days in wet seasons. Avoid overhead watering. Daphnes do not respond well to pruning even under the best of circumstances, but this is the best way to attempt to control this disease. Prune to increase air circulation around shrubs, taking care to sterilize pruning tools by dipping them in household bleach to prevent the disease from spreading. Because the fungus spores collect on the mulch beneath the shrubs, removing the old mulch and replacing it with fresh material may help prevent an outbreak from recurring.
For more information see file on Controlling Fungal Disease.
Foliage Burned because of Dog Urine
Dog urine will discolor daphne branches and foliage, and kill them. Spray vulnerable foliage with anti-transpirant spray to protect it. Where there are chronic problems, screen the shrub or spray its lower branches with pet repellant. Given daphne's delicate constitution, these measures may be as harmful as the original problem, however. For more information see the file on Dogs and Cats