Buffelgrass leaf blight is a disease caused by the fungus (Pyricularia grisea), which reduces the quantity and quality of the foliage and the amount of seed produced by the grass. The study was conducted during 2016 and 2017 in three ranches located in the central region of Sonora, Mexico. The objective was to determine the effect of leaf blight on seed production and the economic impact associated with its presence. Pastures damaged with the pathogen were selected. The evaluated variables were: number of affected juvenile and adult plants, density of plants, production of raw seed, production of clean seed, percentage of shrinkage in the harvested seed, cost of seed, net gain for sale of seed and economic loss due to damage of the fungus. The evaluations were carried out in three ranches using 10 quadrants of 10 x 20 m distributed randomly by site. The data was analyzed by ANOVA. Precipitation was 10 to 40% above the average in all sites and years of the study. The blight caused damage to the grass in all the properties and years evaluated. The results show that, on average, between 46 and 59% of the buffel plants showed some type of damage. Null to very light damage was found in 31.5-36.6%, slight in 21.3-42.8% and moderate in 25.7-42.1% of the adult plants in the 3 ranches and similar affectations were evident in juvenile plants and seedlings. The production of raw seed was affected by the damage of the fungus and varied from 61.4 to 81.8 kg/ha when the damage was null to very light and from 46.2 to 53.8 kg/ha when the damage was light and from 28.6 to 36.9 kg/ha when the damage was moderate. The production of clean seed was also affected by the damage of the fungus and varied from 36.2 to 44.1 kg/ha when the damage was null to very light and from 26.7 to 36.5 kg/ha when the damage was light and from 14.6 to 19.2 kg/ha when the damage was moderate. The seed loss was similar between intensities of damage and averaged 42.1, 37.8 and 47.9% in the buffel seed with null to very slight damage, light and moderate damage, respectively. The cost of clean seed at the average sale $90.00 during 2017 and 2018 and the clean seed of buffel grass produced was 41.27, 30.9 and 17.3 kg/ha for areas with null to very light, light and moderate damage, respectively; which represented a net gain from seed sales of $3,714.3, $ 2,781.0 and $1,557.0/ha., in areas with zero to very light, light and moderate damage, respectively. Consequently, the loss, due to the effect of the fungus damage was $933.0 in the areas where the damage was light and $ 2,157.3 in the areas where the damage was moderate. It is concluded that the leaf blight affects the production of buffel grass seed, so the necessary measures must be taken to reduce its damage.