Answer: Wilting leaves are not necessarily a sign of insect or disease problems so I'm concerned that you gave your shrub two doses of insecticide without seeing any evidence of insects. Spectracide Triazicide is a Soil & Turf Insect Killer and is not registered for use on rhododendrons so you may have done more harm than good by applying it. Malathion is registered for use on rhodies, but again, if you do not see any insects, it's a waste of time, money and energy to apply the product.
I'd look a little further down on the plant to discover the cause of wilting. The stem, where it attaches to the main trunk, may be damaged, which may have stopped the flow of moisture to the affected leaves. Or, there may be some root damage that is causing the distress to show up on the branches. I'd prune off the affected branches and destroy them. Then watch for additional symptoms. If more branches exhibit the same symptoms, dig the plant up and inspect the root system. The roots may be girdled, the soil may not drain well which could cause root rot, or there may be damage from gophers or moles. Herbicides used in the area may have leached into the adjoining soil and affected the roots. There are many possible causes; not all of them are obvious, so do a little investigating.
Hope your rhodie recovers!
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