The book is military Science Fiction. Our protagonist is a retired Marine general (still in excellent physical shape) now living on a farm planet. Alien plants invade. The climactic scene we're seeking for the cover should show:
1) a giant plant creature (humanoid with the following differences):
*legs flowing down and out into ambulatory roots (as opposed to feet)
*arms with the appearance of tendrils and branches
*extra arms, both sprouting from the traditional point but also trailing down the torso a bit
*no ears, mouth, eyes, nostrils (can have the suggestion of a nose)
*all in all, think of a human-shaped topiary or ivy daikaiju as a starting point)
The giant plant creature is tearing apart a massive metal structure used to launch payloads into space (think of a long and curving section of a roller coast, but beefed up).
2) Our hero (the retired Marine general) stands in the foreground looking determined. He should be showing carrying/using a flame-thrower. FWOOSH!
3) Standing beside him is a golden retriever.
The ruins of a few warehouses and concrete bunker-like administration building lay all around but these are minor elements at best. Everything else should be rows and rows of farm land where all the crops have been trashed.