Azaleas are generally healthy plants when their basic cultural requirements are met. However, they are subject to a number of problems caused by infectious agents, insect pests, weather and nutrition deficiencies.
A few common problems and their control measures are mentioned here, organized by the affected parts of the plant. A more complete list of azalea problems is at azalea diagnosis.
Warning: Horticultural chemicals tend to work because they are harmful. Follow their label safety precautions such as gloves and other protective measures to avoid personal harm, and follow their label rates of dilution and application to avoid harm to the plants and environment.
Flowers first appear spotted, and collapse and appear water soaked in a few days. Dead flowers turn brown and cling to the plants instead of falling to the ground. Petal blight is more severe in cool, moist springs.
Petal blight is caused by an airborne fungus which over-winters on the spent flowers. Remove old mulch and replace with new in early spring. Drench soil area under plants with Terraclor in January. Spray with Thylate or Benomyl when blooms begin to open. Continue at 7- to 10-day intervals during bloom period. Good coverage is essential. Bayleton may be used when the buds show color. See ovulinia petal blight for a more detailed discussion.
Upper surface of leaves has a gray, blanched, or coarse-stippled appearance. The undersides of the leaves become discolored by excrement and cast skins.
Spray undersides of the leaves with Malathion, dimethoate (Cygon), or acephate (Orthene). Repeat application every 10 days until control is obtained.
Leaves turn light green to yellow, then creamy white between the veins, while the veins remain green. Chlorosis is usually caused by the soil pH being too high, making iron unavailable to plants.
The soil pH may be lowered by adding ferrous sulfate, finely ground sulfur or iron chelate. Spraying the foliage with iron chelate has a dramatic but temporary effect. See mineral nutrient deficiencies for a more detailed discussion.
Various insects may feed on the leaves, typically notching the edges.
Spray the leaves with Diazinon or acephate (Orthene).
Pale green or whitish fleshy galls, often quite large; leaves are curled or deformed. Leaf gall development is favored by cool, moist weather.
Handpick and destroy the affected leaves. Spray leaves with Bayleton, Ferbam, Captan, or a fixed copper fungicide. Start spraying at end of bloom period and continue at 2- to 3-week intervals until mid-June. See more details at leaf and flower gall.
Brown or bronzed leaves, with tiny black fruiting bodies on the dead tissues. Irregular and colored spots on leaf.
Use Maneb, Ferbam, or Bayleton beginning at the end of the bloom period. Continue at 2-week intervals through growing season or as long as young leaves are present. Refer to the Bayleton label for application intervals.
Leaves become yellow-flecked with stippled areas. Fine webs on leaves may be visible with close observation.
Spray undersides of the leaves with acephate (Orthene) or dimethoate (Cygon). Repeat the application in 7 days to take care of egg hatch.
Leaves turn yellow and plants are stunted. They do not respond favorably to water and fertilizer applications.
No chemical control is available. Other conditions mimic nematode injury; collect a soil sample from root zone for nematode analysis. Check with your County Extension agent for more details, and check plant root rot for other root-related problems.
Usually found on twigs or branches. They can appear in various colors and shapes. Some look like bits of white cotton; others are brownish.
Malathion or acephate (Orthene) can be used as spray during crawler stage. Dimethoate (Cygon) can be used.
Entire branches turn brown and die during the growing season. Look for evidence of bark splitting near base of limbs or at ground.
Use recommended cold-hardy varieties for your area. Keep the plants in good thrifty condition. Avoid fertilizer and cut back on water during late summer to avoid stimulating growth, then water heavily after the first hard freeze to provide moisture during the winter.
azaleas (parent page)