Some of my azaleas have dull, silvery colored leaves. What is causing this discoloration and what should I do about it?
"Thrips are characterized by a silvery white discoloration on the leaf's upper surface and silvery on the bottom with small black frass specks. The damage is similar to that from lace bugs. Thrips are a problem in warm and dry climates like California and New Zealand. Most of the standard insecticides and insecticidal soaps can be used. Control for thrips whether an insecticide or insecticidal soap is a contact control and must be applied on the adults. This is most likely done in May when they are visible. "
"Whitish specks on the upper surface of leaves and dark spots varnish-like on the bottom are symptoms of rhododendron lace bugs, small insects with transparent wings on under-surface of leaves.. They are more prevalent on certain varieties and on plants grown in sunny areas. When damage first appears, it may be controlled by any of a number of contact insecticides. Care must be taken to spray the lower surfaces of the leaves where the lace bugs live. Moving a plant to an area with more shade by aleviate the problem."
My Northern Lights azalea also got to looking really bad from about Aug. I don't thnk it was an insect problem, though; more like powdery mildew. The whole plant now appears silver/white/gray. Not pretty. I planted mine last summer (late), so this was the first growing season in my garden. Next year I'll have to do something about it. Any ideas on specific treatment?
Mildew on the deciduous types is really common here in this coastal location...
Do not overwater or overfertilize plants, as the fungus prefers succulent new growth.
Hand-pick and destroy mildewed leaves to control small amounts of infection.
Hose diseased plants with water when mildew first appears when practical(mornings, do not do this at night). This can help remove fungus and prevent new infections.
Prune and space plantings to allow good air circulation. Do not plant in extremely shaded or damp areas.
And, always practice good sanitation - Rake and destroy fallen leaves year-round to reduce infection source. Do not compost diseased materials.
Chemical control is possible, although I personally prefer to limit my spraying to roses only, spraying not being one of my favorite garden chores. Begin applications when you first notice the disease on current-year leaves.