What about some noise-maker, like a cap gun, that you can fire in the evening as they're settling in? Maybe that will get them nervous about the area and they'll find another roost. Luckily I don't have any experience with large roosting flocks.

Get a couple of those lifesized looking owls and perch them above the grove on poles.

Kt

I've used a motion-activated sprinkler (type in "Scarecrow sprinkler" on Amazon) to keep deer out of my yard, and they work for smaller critters and birds. The main problem for you would be that you would need to mount it high enough so that the birds' movements triggered the sprinkler and they got doused. Here is a video of one in action...

Here is a link that might be useful: Scarecrow vs. pigeons

I have the same problem in my 20x50 grove of yellow groove bamboo and we just cut it down. We are going to kill it out where it's growing and relocate some of it down to a remote location on our property down by the highway about 4 acres away. If the birds roost there, we really don't care. We have cut it all down with pruners, burned most of it and saved some of the poles for projects.

I would see that as a blessing because you can have your grove fertilized for free.

sandy-
You do realize that you can't easily "kill" bamboo? Chemicals don't work. Digging out the root system is the most reliable method. With the size of your grove, I hope you have some large mechanical equipment.