My thoughts are off the cuff.....not to be considered as 'carefully thought out, backed with evidence'...because they are not.

But I have made your mistake, in prior years. In one sense frustrating, in another sense, it seemed not to matter.

That chemical (and I don't know that one. I only know Grub-X, which I assume to be similar) is persistent, and will stay in the soil. It kills larvae (we call them grubs) when the larvae are zero to four weeks old. At that stage, the larvae (grubs) are weak, but later they will become stronger. If, (and it's a big IF) the grubs make it, survive, to five weeks old, the grubs will in fact become moths, and those moths will fly away, and those moths will lay eggs, at the same time every year.

You put your stuff down four weeks late. Maybe only three weeks late. Maybe (it could happen) only two weeks late. In any event, you were late, as far as this year's crop of larvae was concerned: they were already big enough that the chemical won't kill them. Every one of them will become moths.

All is not lost: that chemical (if you don't core-aerate) will stay with the soil, and will prevent any LATER crops of larvae from maturing: those larvae will be killed, when they are very young. That chemical is claimed to last for a year: in my experience, it will last for two years.

So you lost this crop of larvae: they will become moths. But later crops of larvae will die. The moths floating around now will surely lay eggs. Those eggs will hatch, but the larvae will die, rather than become grubs, and then later, moths. All because you put that chemical down on the lawn. Nice work, btw, my compliments.

But this very first crop of moths? You were a tad late.

Don't worry about it.

Keep us advised, let us know how it turns out.

Philes21 - Your explanation makes perfect sense - thank you so much for taking the time to write that out.

I won't enter "panic mode" just yet!

Best -
Brad in MA.

I hate to disagree with Philes, but the insecticide that you applied was not directed at grubs, but rather some more common insects, and will kill off your moths very soon. Yes, grub control products have a small range of effectiveness, but what you applied does not. So don't worry about the moths! You haven't made any mistake, and they will all be gone soon.

Cheers,
Paul