Originally Posted by phasthound
That's a good point.
Here is the reply I received from Rich Buckley at the Rutgers Plant Diagnostic Lab regarding break though with Merit.
I have not heard anything specific for this year, but I don't doubt there were control failures. Merit will not control asiatic garden beetles. It is known that they will invade areas as a secondary pest once the oriental and japanese beetles are removed by the product. I also suspect that due to the dry mid-summer period that egg-hatch was delayed until late-August when the rains started again. If you applied Merit as per the label in May, then it was probably used up by then. I think it best to use Merit when the adults fly in late-June or July so it lasts through late-summer into fall.
This is put perfectly. Going back a few years ago I had breakthrough and suspected this was the case. Since that time I have been applying very late June, early July with no problems. Other than a more plentiful naturally occuring watering-in, there really isn't any reason to apply Merit so early anyway. Apply later and get protection deeper into the season where the problem presents itself anyway! Good stuff.