You're totally correct, Agnetha. If end is understood to be a noun and the object of the verb agrees, then it needs a preposition before it -- "Moscow agrees on end to vegetable ban" would be the best choice in this case.

(On the other hand, you could also construct the sentence with end functioning as an infinitive verb: "Moscow agrees to end vegetable ban" -- so it's not clear which construction the headline-writer intended to use. But in any case, someone f*&ked up in the editing process!)