Both sport the exact same ingredients, but the 992 is much darker in color than the Mecamine, and they even smell different. So -- 1) Mecamine-D is a more "clear" product that tends not to stain (as much) when spraying on siding & foundations. 2) Trimec 992 is much darker, so it tends to leave stains on the sides of buildings. I figure the difference must be in the way they manufacture their stuff. On the other hand, neither of the above herbicides kill difficult weeds for sh$t, so we spike with Chaser ester. Anybody have opinions? rscvp, thanks.