In La Laguna and Daza small towns Pasto – municipality, placed from 2.600 to 3.000 masl on Freziera canensces have been appearing alterations characterized by circular foliar spots with a white center, black eminent points and a nechrotic halo that spreads over the whole foliar area causing with time a reddish color, in its final stage turns into a brown color and later the tree defoliation. Field observations indicate a wide distribution of the disease. The objective of this investigation was to determine the causal agent of the disease; for it, samples of necrotic tissues present in the affected plants leaves in field were collected. The corresponding PDA cultures were realized in the microbiology laboratory of the Nariño University, achieving to isolate two k i n d o f colonies. The first one was characterized by being cottony of white color with yellow or salmon – pink center and black back, in the center with yellow haloes and white at the edge, and the second one of white color and gray center and cottony aspect. Also at microscope observations were found pycnidiums, with thin and elongated conidias structures characteristics of Septoria genus. The patho- genicity test with plants of seven months of age, to a concentration of 1x105 conidias.ml-1, they allowed the recovery of similar field symptoms, which it verifies that Septoria sp. is the motilón (Freziera canensces) ash spot causal agent.