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Objective. To isolate and identify the causal agent of leaf spot (LS) in Cocos nucifera L. var. Brazilian green dwarf (BGD) and to evaluate the in vitro effect of biorational products in inhibiting the growth of the phytopathogen. Materials and methods. The causal agent was isolated from leaves with LS symptoms and identified morphologically. Five biorational products (Jaque Mate®, Fullkover®, Hongo cero®, Sigatoxx®, and Timorex Gold®) were evaluated in vitro at doses of 2.0, 1.0, 0.5, and 0.25% v/v added to the PDA culture medium. In the center of Petri dishes, 5 µL of a conidiospore solution (9.2×104 conidiospores/mL) of the phytopathogen was inoculated. Colony diameter (CD) was measured, the percentage of mycelial growth inhibition (MGI) was calculated, and the LD50 and LD90 were obtained. Data were analyzed by analysis of variance and Tukey multiple comparisons of means (P=0.05). Results. Bipolaris sp. was diagnosed as the causal agent associated with LS in C. nucifera. Jaque Mate® at all doses, Sigatoxx ® at 2.0 and 1.0%, and Timorex Gold® at 2.0% prevented the growth of Bipolaris sp. with 100% MGI. The lowest LD50 was for Sigatoxx ® (3.67%). Conclusion. Jaque Mate®, Sigatoxx®, and Timorex Gold® were the most effective extracts in inhibiting the growth of Bipolaris sp. isolated from C. nucifera BGD. [ABSTRACT FROM AUTHOR]