Starf

Starf is a type of Berry that can be planted in the Farm. It can be obtained by having at least 1 empty plot while encountering a shiny wandering pokemon. The Salac or any later berry must be unlocked to unlock this berry. It emits an aura that increases the Shiny Chance.

Possible Planting Formations
You can fill your Farm in the following way to obtain this berry. Note that the setup omits a 24th Roseli as that would allow the mutation of the Custap which would occupy the empty plot.