Dead Knockout Rose Bush
I have a knockout rosebush that completely died almost overnight. There was no obvious indication of disease and the knockout rosebush right next to it is fine. It appears to be firmly rooted - does not pull out. I am wondering if it might have been sprayed with something.
There is a good deal of weed competition at the base of the shrub. Is there any chance that an herbicide was applied to them? There is a piece of creeping charlie/ground ivy that looks like it's browning within the rose on the left side.
It does look like it could be a root issue. Is the area well-drained? Any chance it's been sitting in a wet area? There are root rot diseases that can take plants down pretty fast, though not usually overnight.
Otherwise, we don't have a good answer for you.
No, I have been pulling the weeds by hand. I don't use any herbicides. At all. What my concern is that someone sprayed my rose bush with herbicide, but was running it by you guys to see if there could be any other reason this might happen. I have a problem with a neighbor who consistently lets his large dog(s) pee and poop on my plants and shrubs and I have been having to go to extreme lengths to keep them from being able to get to them. Some bad blood between he and I, and him and some other neighbors. Thinking he might have done this, but have no proof, and am trying to rule out any other cause. Most of the weeds look fine and appear to be growing well :-(. I pulled on the bush to see if it was loose in the ground and/or would pull out, and it wouldn't. It is firm. I have cut it all the way back, as far as I could and am hoping it will come back. Area is well drained and it hasn't been sitting in water.
The only other possibility we can think of might be physical damage to the base of the plant or roots (e.g., vole chewing). If an herbicide had been applied on the rose bush, it would be killing the weeds on/near it as well. If you saw healthy green growth/stems at the base of the plant when you cut it back, it should regenerate.