We've noticed that our mature silve maple tree is raining this sticky mist of sorts. We can't see it happening but the lower leaves and ground around it are covered in this stuff... any thoughts, suggestions or advice would be appreciated.
Aphid infestation can cause this. Take a look at this site and scroll down to the third paragraph of page 4. It is recommended not to spray and let the predatory insects take care of the aphids.
If you feel you need to spray, take a look at these sites for environmentally friendly ideas.