3 year old Japanese Lilac trees
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That same late spring frost that browned your leaves, probably killed off your flower buds as well. Since Japanese Lilacs are early bloomers, they are prone to this type of damage. This has been a very prevalent problem across the state this year primarily due to the unusual weather.
You can verify frost damage by cutting into a bud. Brown on the outside, green on the inside=frost damage.
There's nothing to be done this year, just hope for a more normal spring in the coming year.