This two years study investigates a severe diseases outbreak causing heavy economic and environmental losses in a public park at Kurukshetra, Haryana (India), where a virulent strain of the white-rot fungus Ganoderma species caused a heavy mortality rate of 75 % of Albizzia lebbek (siris) trees. Field survey revealed that the hyphal colonization targets the lignin and cellulose within the root xylem and vascular cambium, disrupting water and nutrient translocation. This leads to progressive crown wilting, bark splitting at the collar region, and eventual tree's mortality. This fungal pathogen is identified a new species of Ganoderma (stipitate, varnished, kidney- to fan - shaped, reddish- brown shiny cap with concentric zones, a lateral small stipe, and creamish underneath), infecting exclusively A. lebbek population, revealing host specificity. This taxon is distinct than other species reported on A. lebbek and is named Ganoderma lebbekicola sp nov. The disease can be treated by using chemical fungicide (e.g., hexaconazole, propiconazole, or Bavistin), myco-fungicide (Trichoderma harzianum or T. viride), or integrated applications of both, and preventing the dispersal of conks in the fields.