Playing fetch

If anyone could help me with this it would be much appreciated and thank you in advance.....

My doodle, Jacoby, is five months old and a very loyal and obedient puppy. He knows all if his commands and he listens very well when he is off leash, even around other dogs.
The one thing I have trouble training is playing fetch outside. Outside is key here, becuase he will play fetch for an hour, with any toy I throw, inside the house. The commands I use are "go get it", "bring it back", and "drop it". He loves to play this game and half the time I dont need to use any commands.
When he goes outside, he loses all interest in playing fetch, or for that matter, any toys at all. He wont even chase a ball if I throw it. The only thing he will chase outside are sticks.
Currently, I am trying to use a ball that is only his "outside ball" and a frisbee. He shows excitement when I show him the toys, but very little interest in playing once the ball or frisbee leaves my hand. He will just pick up a stick right infront of him and give it to me.
I tried using sticks as a fetch toy, but, living in a wooded area with so many things on the ground, he will just pick up another stick that is on the ground.
I tried having him play ball around other dogs who play fetch, but he just wanted to play with the dogs.
It seems he is just not interested in fetch or interested in any toy unless its played inside.
I think that he associates toys and chewable items with being inside. However, I dont want to take toys away from him inside the house, as he is a puppy and needs things to chew. If anyone has experience with this or any ideas, feel free to share.