Phenology of four poisonous Senecio (Asteraceae) species in southern Rio Grande do Sul, Brazil

This Study aimed to determine the phenology of Senecio brasiliensis, S. oxyphyllus, S. heterotrichius and S. selloi, and their relationship with cattle poisoning in the southern region of the State of Rio Grande do Sul, Brazil. The phenology was studied during two years in the rural area of the municipalities of Bage and Capao do Leao. These phenological observations were made at monthly intervals during the vegetative phase, and every 15 days during the reproductive period. The plants were observed from emergence until the dispersal of seeds, considering their vigor and their relationship with environmental factors. The results indicate that whenever the environmental conditions, like moisture and light, were favorable, Senecio spp emerge. The vegetative phenophases are practically constant during all life cycle of the plant and the whole year. Unfavorable environmental factors like water stress, soil management and damage by insects, associated or not, can alter the cycle of the plants and determine their permanence in the environment. The majority of the species studied behaved like annual and monocarpic plants. According with the permanence during the two years of observation, the most persistent species in the environment was S. heterotrichius (15% of the plants persisted during the two year period), followed by S. selloi (2,8%) and S. brasiliensis (0,9%). S. oxyphyllus did not persist for more than one year.