Roads are not plantable space.
Can not ban a player for planting in the wild no matter if it might be used as means to stop players from moving goods by shortcuts.
Only bannable offenses are blocking NPC's, Points of Interest, Bridges and other resources at peace you would otherwise have no ways to counter.This has been said at lenght, as well as that several screenshots are needed in different span of time, to determine longetivity of the block being done.So that it can be seen if someone has been there with their cart for several in-game hours, or just for a short while.