Stoner,
You can buy a product called "Seven" , it comes in either a thick liquid concentrate or a Powder it is a white product, Mix to recommended strentgh and spray.
From what I have researched about the Earworms , you must spray the Stalk when the first leaves are coming off the stalk that will eventually produce the Cob. And keep it sprayed (After Rains) until the shoot is completely closed and silk is hanging. During this stage is when the moths lay the eggs of the larvae. If the stalk is sprayed later once the Leaves have rolled up to start producing the Cob it is to late the larvae are already protected and inside the "COB" spraying may help a little but you will still have alot of wormy corn.
Dan