When the horse has kicked its way out of the barn, you do what you have to do. :-)

Neem oil is an effective but pretty wide spectrum control for leafhoppers. You can get it at your local big box store in most cases--Bonide makes a concentrate that I remember seeing at my Home Depot. Plus it's organic and relatively harmless to humans and pets.

That having been said, most insecticides are going to wipe the deck of beneficial insects as well (Neem oil will do that too). It's not a great idea to do that too often, and it would be better if you could manage natural controls in your lawn.

Ladybugs are leafhopper hunters so encouraging their populations would help. There's plenty of resources online for ladybug habitats and whatnot.