Around the same time, GK decided he hated vegetables because all the other kids at school hated vegetables.
Threats do not work with GK. They never have. I've had to use a lot of stealth techniques in the areas of both vegetables and reading to maintain his appropriate growth rate.
The Bait and Switch
I pretend I can't find X vegetable or book. "Why don't you do Y instead to fulfill your requirements?"
If you eat X number of vegetable pieces (read X number of pages), you can play X minutes on the Xbox.
We take GK to see X movie ("Hey, there's a book about X movie, but don't read it"). Or we order X vegetable at a restaurant and say he can't have any. GK will partake because thinks he's getting away with something.
Since GK loves the Halo video game and Strawberry Pop-Tarts, I'll say, "Why don't you read a Halo novel while snacking on fresh strawberries."