Pineapple is among the major export commodities in the Philippines. A species of Fusarium was found for the first time to be consistently associated with diseased leaves collected from MD2 'Super Sweet' pineapple plantations in South Cotabato and Davao City. Test of proof of pathogenicity of the fungus following Koch's postulates and bioassay test of FosetylA1 products against the fungus were conducted. For the bioassay, the treatments used were the following: 1) untreated; 2) Fosetyl-A1, Brand X at 2.25 and 5g/L water; and 4) Fosetyl-A1, Brand Z at 2.25 and 5g/L water. The experiment was laid out in Completely Randomized Design with three replications at three plates per replicate. The data was analyzed using Analysis of Variance and treatment means were compared using Tukey's Honest Significant Difference. Symptoms of the disease included lesions, which later turned into brown, necrotic tissues at the base of infected pineapple leaves, while advanced symptoms showed infected tissues with dark brown to black margins, later dried up and became soft-rotted. The fungus produced cottony white aerial mycelia on the cut surface of the tissues planted on Potato Sugar Agar (PSA) medium. Mycelia were hyaline and septated. Macro-conidia were single-celled, slightly curved, and sickle-shaped with three or more septates. Pure cultures turned light purple after eight days of incubation in full strength PSA. Chlamydospores formed after two months of incubation. Based on cultural and morphological characteristics, the fungus was identified as Fusarium sp. Bioassay results showed that Fosetyl-A1 Barnd X and Z at 5.0 g/L water significantly inhibited the growth of Fusarium sp. infecting pineapple leaves from 97.9 to 100%, respectivel, after 9 days of incubation.