Allelopathic potential of Ageratum conyzoides at various growth stages in different habitats

Allelopathic potentials of volatiles from Ageratum conyzoides were studied at four growth stages (4-leaf, pre-flowering, peak flowering and mature growth stages) in plants growing in three habitats [cultivated field (no shading), roadside (no shading) and under the citrus canopy in orchard (50% shading)]. The allelopathic potentials of A. conyzoides were stronger on weeds and pathogens at peak flowering than at other growth stages. Its allelopathic potential was very strong on roadside, but very weak under the citrus canopy in orchard. Thus, its allelopathic potential varied significantly at different growth stages and in various habitats. Its volatiles were analyzed and their components were identified, which varied at different growth stages and habitats. Further, the inhibitory effects of volatiles and its major components (precocenes, beta-caryophyllene, (beta-bisabolene and (beta- farnesene) were evaluated on weeds and pathogens. The combined strong effects of these components indicated synergism among the allelochemicals.