All four of our 50' high Swedish Columnar Aspens have, for the 2nd year, lots of "floppy" branches that are, well, flopping over. In a couple of sections near the tops, there's a long patch with no leaves or branches and then a bunch of leaves creating a puff of leaves effect. There's no borer disease, thank God. But why the floppy branches? Growing too fast?
Growing too fast, or storm damage. Don't fertilize it. Cut back on water starting in August. Given that most of the fertilizer that reaches it will be excess from your lawn, you may have to reconsider your priorities.
Poplar, if they get a heavy snow load (massive wet snow) will bend. Cells on the inside of the curve are crushed, and the tree/branch won't straighten out.
Treatment: You can either temporarily tie the branch in place or cut it off. Both require ascending the tree to get to the affected branch. A good extension ladder, light weight, and slow movement.
To remove the old branch you only need to reach the base of the branch. Cut it off about a foot from the trunk. It may sprout new twigs which will fill the space.
To salvage the branch ascend to about the mid point of the branch and tie it to the trunk using women's nylons or a section of panty hose. This has the following characteristics:
- It distributes the force over a large area and doesn't cut into the bark.
- It's stretchy enough to accommodate branch movement.
- It doesn't hold water, dries quickly after a rain, so it doesn't foster rot.
- Sunlight degrades the plastic and it falls apart after a few months, so you don't have to make a second trip up the tree to retrieve it.