That's the handiwork of the Azalea Lace Bug. If you look on the underside of a leaf, you may see the adult of the culprit species, a 1/8" long insect with transparent wings marked with a lacy pattern in a grayish brown. The suck sap from the leaf, causing light stipple marks, and a heavy infestation will pretty much suck the color out of the leaves. If you don't see an adult, you're sure to see lots of diagnostic black dots which are either cast of skins of the larvae or excrement deposits. Evergreen azaleas are their main target, although they will attack deciduous types, too. Azaleas planted in sunny sites are victimized much more than those in shade.
HOW TO CONTROL:
Control consists of using repeated foliar sprays containing acephate, horticultural oil, a pyrethoid like bifenthrin or cyfluthrin, imidacloprid, or disulfoton. (Don't get scared by all that jargon!) The last two have a systemic action, which means they're absorbed by the leaves into the plant's system to give longer protection. Pesticide containers always list the active poison on the front label, so look there for any of these chemicals alone or in combination.
Spraying should begin in early spring when the overwintered eggs start hatching (around the first week of April is a good rule of thumb for Middle Tennessee), followed by another application about 10 days later, and then once a month or so to catch any interlopers that come in on the breeze.
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