A novice farm boy cultivates the friendship of a scarecrow to save his farming heritage from a witches brewing scheme and win the farmers cup.

The logic employed in the concept is unclear. Has the scarecrow been animated by an external force? Is it a magical scarecrow? What kind of Scarecrow is this that the boy will be able to communicate with it?

I would change it to “…friendship of a magical scarecrow…” this way you’re stating genre as well and as a result justifying the super natural elements.

The wording of “…cultivates the friendship of…” feels wrong if this was a business relationship or coworker etc… the verb cultivates can work but if it is a boy and a magical (or what ever type it is) scarecrow then it feels wrong. Perhaps just name a spade a spade and say the boy befriends a magical scarecrow? The semi humorous connection between cultivate and farming is not enough to justify using it either.

Lastly saving the farm seam much higher stakes than winning an obscure farmers cup, cup in what competition exactly to that matter? Best to describe one main goal rather than two unrelated ones of differing stakes.

I put in an inciting incident as the logline was lacking one:
After a witch destroys most of his parents farm a novice farm boy befriends a magical scarecrow to help him kill the witch and save his family home.

Hope this helps.