Methods, systems, and controllers for detecting and mitigating well screen outs may include a controller configured to operate a fracturing pump to supply fluid at a discharge rate to a wellhead at a fracturing well site. The controller may also operate a blender positioned to deliver a blend of proppant and fluid to the fracturing pump. The controller may compare a fluid pressure increase rate to a preselected increase rate indicative of a potential well screen out. The controller may incrementally decrease the discharge rate of the fracturing pump and a flow rate of a blender when the fluid pressure increase rate of the wellhead exceeds the preselected increase rate and the fluid pressure is within a preselected percentage of a maximum wellhead pressure until the fluid pressure of the fluid supplied to the wellhead is stabilized.