Mango Plant Health Initiative Act This bill establishes a research and extension grant program for a mango plant health initiative. Specifically, the bill authorizes the Department of Agriculture (USDA) to provide competitive grants for studying potential resistance and tolerance of mangos to native and nonnative disease and insect pests; conducting research for treatment of pests that affect mangos; conducting field studies to evaluate cultivars of mangos with enhanced resistance to diseases and pests; educating growers on best practices to promote the safe production of mangos; and establishing area-wide integrated pest management programs in areas affected by, or at risk of being affected by, specified pathogens or pests. The bill also extends the authority for several existing USDA high-priority research and extension initiatives through FY2028.