Thank you for reaching out to ask2.extension.

The top picture looks like lilac bacterial blight as you said and the middle is powdery mildew.  Both are factors of the really wet spring/early summer we’ve had.

Powdery mildew is really common on lilacs, especially when the weather is wet.  It will not hurt you bushes, just doesn’t look great.  You can thin the branches out to promote air movement.  No treatment necessary.

If your lilac bush does have infection, prune and burn all infected parts as soon as you notice them. A spray of a copper-based pesticide, which is organic, during the early spring each year should help prevent the problem before the buds begin to break.

I’m not sure that treating them now will help.  The copper based solution has temperature requirements.  Pruning out and getting rid of the infected branches may help with control.  Be sure to disinfect your tools before moving on to another plant as it can spread.

Good luck!