Carbamate 2 gallons per acre plus wetting agent will knock them down. You need to apply it with lots of water 5 gallon per k or more.
Carbamate will kill everything including earth worms. it has the broadest label of all pesticides. It is also one of the more environmentally unfriendly chemicals.
Stay with Merit if it doesn't work Bayer will give you Dylox for free. But you have got to sign up on there program on the web.