Biomass production and essential oil yield in Ageratum conyzoides L. - Asteraceae in different stages of development

An experiment was carried out at Sao Manuel Experimental Farm, FCA-UNESP, B otucatu-SP? in 1994 and 1995, aiming to determine the biomass production an d essential oil yield of "mentrasto" (Ageratum conyzoides L. - Asteraceae) in different stages of development. The statistical design used was a complete randomized block with 8 replicat ions and 3 treatments (pre-flowering, flowering and post-flowering). The sp acing was 70 cm between rows and 50 cm between plants, with 70 plants/parce l. The seedlings were transplanted 40 days after sowing. After harvesting, the fragments (roots, stems, leaves, flowers) and whole plants were washed, se parated and weighted. The extractions of essential oil were done by hydrodi stillation, using Clevenger apparatus, for two hours. There were statistic differences (Tukey 5%) in fresh weight of all vegetal parts when harvested in different development stages. About essential oil y ield, statistic differences were not verified among the treatments.