Maggie wrote about treating lacebug infestation and nesting birds. Since no
one else has responded, I'll contribute what little I can.
First, I think the young birds will fledge and leave the nest pretty soon,
leaving the place vacant. Then you can spray whatever you want.
Second, I also wonder what other course of action you could take to stop this
yearly cycle of trouble with the bugs. Maybe a very good cleanup at fall,
disposing of infected debris completely? If it is a smudge that smothers the
leaves as you wrote, could you spray them down with a weak, soapy solution
through the season?
I hope someone more knowledgeable will respond. I'd like to know too!