I think I cut down these trees in April, since they were blocking one of the highbush blueberry bushes. Blocking as in growing right through the thing. As you can see, they're doing their best to make up for lost time - these shoots are about 3 feet high already.
I've told several people about all the work I did this spring to eliminate all non-blueberry trees from the blueberry bushes(like that worked - hah). One old-timer told me that what I should have done was just cut everything down about a foot above the ground. The blueberries would love it, and it would give me a better chance of actually getting rid of the bad guys.
I recently got a book (Backyard Homesteading) that says the same thing. For old blueberry bushes that haven't been maintained, cut them entirely down a little above the ground. I think I'll try that this fall or next spring on a few of my bushes to see how it goes. Just need to figure out if I have to dig out the invaders or if there's something else I can do to get rid of them.