Answer: When flowering shrubs won't bloom it usually means they're not getting enough sunshine or they're being pruned at the wrong time. If the leaves are drying up and falling off, and you have a whitish coating on the leaves, it's a sure sign of powdery mildew, due to lack of sufficient sunshine and poor air circulation. I'd prune the shrubs way back to remove the fungus and to open them up to better sunlight penetration. If they're not getting all day sunshine, you may want to move them this winter so they can get a good start next spring. Once they're in the proper exposure to sunshine, they should bloom and they should be more resistant to fungal diseases.
Best wishes with your lilac shrubs!
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