Is your infestation light or more severe? If it's somewhat light to moderate, I would say do the best you can to just reduce numbers if their natural predators (lacewings, ladybugs etc) are not doing their job.

While it should never be your first line of defense, if the infestation is severe and you cannot get the lace bugs under control, you have the option of using a systemic chemical, absorbed through the leaves into the plant.
A systemic insecticide works from the inside out instead of only on the exterior surface of the treated plant - total coverage of all leaf surfaces isn't necessary.

I had never seen lace bug here, I thought our climate not right for them, but I bought acephate and sprayed for a heavy infestation of lace bug at my SILs last weekend. Five 6'+ and wider than tall rhododendrons all in the same rear area of her back garden, live adults and nymphs were present and in huge numbers, I noticed the off color of the shrubs from some distance inside the house and went out to see what might be wrong.

effie, I just noticed you said lace wing damage - make sure you know what you are targeting with your controls:

lace wing.... good guys
lace bug.... bad guys

Bayer Advanced Tree and Shrub treatment will control lace bug systemically through the roots, although it may be too late this year to use it. The Bayer product is based on Merit insecticide and is expensive, but probably worth it if you have not too many plants to treat. If you control lace bug for 2 years or so, infestation will be greatly reduced. Once the lace bug population reaches a certain level, damage can be quite serious - rhododendrons are not killed outright, but are seriously weakened over time.