I think that borers are still active into August when they pupate and turn into little brown cases in the soil. I have not seen any so far in that stage. That is why digging around to share or divide in August is good for finding those if you know what to look for. I think late August and September is when the moths emerge and lay eggs.
I am still finding some borer activity even though I have put down chemicals several times. You have to be vigilant.
