That looks like an artillery fungus. It's called that because it shoots masses of spores through the air, sometimes for several feet. The wind can pick them up and carry them further. It likes decaying wood, e.g. shredded wood mulch, and helps the rotting process along. It's a natural part of the cycle, and if that's what it is I doubt it's the cause of your plants' deaths.
You can help the HubPages community highlight top quality content by ranking this answer up or down.