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In the United Arab Emirates (UAE), royal poinciana (<i>Delonix regia</i>) trees suffer from stem canker disease. Symptoms of stem canker can be characterized by branch and leaf dryness, bark lesions, discoloration of xylem tissues, longitudinal wood necrosis and extensive gumming. General dieback signs were also observed leading to complete defoliation of leaves and ultimately death of trees in advanced stages. The fungus, <i>Neoscytalidium dimidiatum</i> DSM 109897, was consistently recovered from diseased royal poinciana tissues; this was confirmed by the molecular, structural and morphological studies. Phylogenetic analyses of the <i>translation elongation factor 1-a</i> (<i>TEF1-&#945;</i>) of <i>N. dimidiatum</i> from the UAE with reference specimens of Botryosphaeriaceae family validated the identity of the pathogen. To manage the disease, the chemical fungicides, Protifert^&#174;, Cidely^&#174; Top and Amistrar^&#174; Top, significantly inhibited mycelial growth and reduced conidial numbers of <i>N. dimidiatum</i> in laboratory and greenhouse experiments. The described &#8220;apple bioassay&#8221; is an innovative approach that can be useful when performing fungicide treatment studies. Under field conditions, Cidely^&#174; Top proved to be the most effective fungicide against <i>N. dimidiatum</i> among all tested treatments. Our data suggest that the causal agent of stem canker disease on royal poinciana in the UAE is <i>N. dimidiatum</i>.