It's the time of year when I begin highly discouraging the use of pruners, loppers, saws, or any other implement used to cut woody plants. I usually tell people to just forget about pruning trees or shrubs from about the middle of August through leaf drop.
The why, if you think about it, is quite logical. Pruning sort of re-invigorates the plant. Makes the plant want to send out new shoots. If a little new shoot emerges below a pruning cut that's made September 1, it usually won't have time to produce wood and harden off completely before our first frost (about October 15). That makes for a dead little shoot.
Unfortunately, this dead shoot can then be the entryway for rotting organisms, like fungi or bacteria. Once they're in, they're in. And the rotting will begin.
The link above is UK's publication called 'Pruning Landscape Trees'. Here's the link to another called 'Pruning Landscape Shrubs'.