i'll 2nd the 3 weeks waiting period. i spot sprayed some generic sethoxydim in my clover. after one week the grass looked just like it did the day i sprayed it. i presumed that the stuff was old or that i had done something wrong since when i use gly on grass i can tell a difference after a few days, let alone a week. but about 3 weeks later i checked it and the grass patches were very brown.