Abstract: An applicator assembly for applying hot melt adhesive to a substrate such as the end flaps of a sift-proof carton includes slot nozzles employing elongated, wear-resistant doctor blades formed with a fluid discharge slot. The doctor blades, preferably in the form of hardened steel plates, are releasably clamped to the body of the applicator in communication with the outlet of an internal passageway in the applicator body which receives adhesive from a flow control device such as an adhesive gun. The plates forming the doctor blades are separated by a shim to define the fluid discharge slot into which the adhesive flows from the internal passageway. The lowermost ends of the doctor blades are formed in various configurations to spread the adhesive in the desired pattern or thickness on the substrate depending upon the type of adhesive employed or the requirements of a given application.