Vegitable oil serves more to create a barrier than to kill the ants, but, they will be killed by suffocation but, that takes a few days. As for keeping weeds down, I just keep my bees about 8 inches off the ground on cinderblocks and, I actually layed concreate below the hives but, the ones which I couldn't (land doesn't belong to me) I just put some old fallen shingles from the last hurrican for the two feet infront of the hive. That keeps the weeds and grasses down just fine.