Around the same time, GK decided he hated vegetables because all the other kids at school hated vegetables.
*sigh*
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?"
The Bargain
If you eat X number of vegetable pieces (read X number of pages), you can play X minutes on the Xbox.
Reverse Psychology
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.
Substitutions
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."