Maybe our chem salesman is churning my account. I think it has to do with the cycle of the insects and grubs that are hatching out at different times. They don't get killed unless they munch on the turf and I'm sure the residual is much lower by the end of summer so you need a second app. But hey I do what my salesman tells me to because there is no way I could keep up with all the new products and do my job.
Bad thing is I have birds drilling in the greens for something and I may have to use some old Dylox I have in between apps of Arena. After all the money I spent.