A replaceable tray for inserting into an exit path of a bee hive includes: (a) a tray body having a base and at least one side wall extending upwardly from the base and surrounding a periphery of the base, the base and the at least one side wall defining an interior of the tray body, and the at least one side wall having an upper end defining an upper rim of the tray body; (b) a removable top bonded to the upper rim for sealing the interior of the tray body; and (c) a powdered plant treatment agent in the interior of the tray body and supported on the base when the tray body is upright.