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In vitro studies using detached inflorescences with peduncles were conducted to investigate flower abscission agents in North American ginseng (Panax qulnquefolius L.). Of the nine compounds studied only three, ammonium thiosulphate (ATS), abscisic acid (ABA) and ethephon induced abscission. Anilazine, benzyladenine, carbaryl, gibberellic acid, napthaleneacetic acid and thidiazuron did not induce abscission. ATS dip treatments did not induce abscission but the spray treatments induced 60.5% abscission at 1500 ㎎·L-¹ and 33.1 % at 3000 ㎎·L-¹. Severe chlorophyll loss occurred on all inflorescences treated with ATS. Both ABA dip treatments and a 250 μmol·L-¹ spray treatment caused abscission (40%) without adverse effects, and timing of ABA application was important. Because ABA was only significant in the dip treatments, ABA may not be a practical option for field use on ginseng. Ethephon sprays induced more abscission as the season progressed and as the concentration increased. As the dip concentrations of ethephon increased, the abscission rate decreased and the health of the inflorescences declined. The 1500 ㎎·L-¹ spray of ethephon gave consistent abscission results over the growing season with little phytotoxicity. Treatment with the competitive ethylene inhibitor 1-methylcy-clopropene (1-MCP) suggested that flower abscission was due to the liberation of ethylene from the breakdown of ethephon.
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