| Parthenium hysterophorus L. of the family Asteraceae is an exotic noxious weed from Central America. It has caused serious health, environmental and agricultural hazards in Southeast Asia, and now widely distributed in the tropical and subtropical regions in China. In this paper, the main biology and ecology of the weed were examined systematically in order to explore the invasion mechanism of the plant, which could provided some reference for scientific and effective control on P. hysterophorus, and a set of techniques of chemical control on P. hysterophorus were established. The main results were summarized as follows:1. P. hysterophorus had epidemic spread and strong reproductive potential. The weed could produce 7500-10000 seeds during its lifetime. The mature seeds had the characteristics of abscission and dormancy. The length of the seed was 1.0-1.5mm and the thousand-grain weight was 0.74-0.76g only.2. The seedlings emergence rate of P. hysterophorus had a close relationship with the burial depth of the seeds. The seeds which laid at the soil surface had the highest seedlings emergence rate, and the seeds could not emergence at all when the burial depth of the seeds was over 1.5cm.3. P. hysterophorus developed easily to be a dominant population in its invaded area, and had inhibitory effect on the growth of local plants by its allelopathy, which affected the biodiversity of invaded area. In the environment which P. hysterophorus had planted, the Indices of Species Richness, Dominance and Evenness were only 1.91-2.31, 0.54-0.63 and 0.56-0.62, respectively.4. P. hysterophorus had allelopathic potential which may serve as an important invasion mechanism of the weed. The allelopathy of the aqueous extract from P. hysterophorus on Raphanus sativus L., Cucurrds sativus L., Digitaria sanguinalis (L.) Scop, and Bidens pilosa L.were determined by measuring the seed germination and seedling growth of the plants. The results indicated that the aqueous extract showed someway stimulating effects on seedling growth of R sativus and C. sativus at a concentration of 0.01 g·mL-1. But at a concentration of 0.05 g·mL-1, the aqueous extract got inhibitory effect on the seedling growth of R sativus and C. sativus. The aqueous extract significantly inhibited the seed germination and seedling growth of D. sanguinalis and B. pilosa at four concentration (0.01,0.05,0.15 and 0.50 g·mL-1) . The exudates from the root of P. hysterophorus had inhibitory effect on the seed germination and seedling growth of D. sanguinalis and B. pilosa.5. Six kinds of herbicides were screened on the toxicity against P. hysterophorus through pre-emergence application and foliage application. The results showed that bensulfuron, atrazine and ametryn had a good control effect on P. hysterophorus with pre-emergence application, and metaxon, ametryn and atrazine showed well-controlled activity on this weed with foliage application in early post-emergence period.6. Field test results showed that the pre-emergence and early post-emergence were the most suitable periods for control on P. hysterophorus. The best control effect on the weed was attained by appling bensulfuron at a dose of 30-40 g·ai/ha, or (acetochlor+atrazine) at a dose of 500-600 g·ai/ha +21 g·ai/ha, or (acetochlor+atrazine) at a dose of 405 g·ai/ha +150-450 g·ai/ha at pre-emergence period. Besides, the best control effect on P. hysterophorus was attained by spraying metaxon at a dose of 840-1260 g·ai/ha, or ametryn at a dose of 1200-1920 g·ai/ha, or (acetochlor+atrazine) at a dose of 405 g·ai/ha +150-450 g·ai/ha on the weed at 3-4 leaves stage.
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