I forget where I've found it, but nano-particles do sometimes have significantly different health effects than larger particles.<p>And personally, while I LOVE glass bottles / glazed ceramic things, as it's nigh-tasteless and doesn't have nastiness in it, spraying plants with this makes me worry about <i>ingesting</i> it in (relatively) large doses.  I doubt people have been eating glass to see what health effects it's had, so it's probably going to fall into new research... and if it's that effective, I'd be willing to bet companies will cover up research that would be bad for their business.