Attempted to use it for spider mites and fungus gnats in indoor weed plants. Spider mites were unaffected and fungus gnats may be dropped down a bit in activity initially, but once watered they were back. More application of the DE to the soil restricted water flow considerably from the top, especially as more DE was applied. The yellow sticky traps were very effective for the fungus gnats, as were predatory nemotes. As far as outdoor goes, I used it to attempt control just about everything, but didn't see any real difference, so I applied pest specific products which gave immediate results like BT, Captain Jack's Deadbug, pyrethrin, Dr. Doom, Azamax and a few others that are escaping me. One summer I was getting tons of ants inside, so I thought I'd try out the ever failing DE to see if that did anything to them. I dusted it around baseboards to make a barrier, and those fuckers just walked right over it like ain't no thang. In theory DE seems like a great product, but in field use it failed miserably, in my experience.
No, it won't kill plants, just like it doesn't seem to kill bugs. Might have better luck with chalk, imo.