Paraquat resistance in the broadleaf weed Crassocephalum crepidioides (Benth.) S.Moore from the Cameron Highlands, Malaysia

B.S. Ismail, T.S. Chuah and K.H. Hussin, School of Environmental and Natural Resource Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM, Bangi, Malaysia.


A paraquat-resistant broadleaf weed, Crassocephalum crepidioides infesting tomato and cabbage fields in Tanah Rata, Cameron Highlands, Malaysia was identified in a greenhouse study. Paraquat dichloride at 1 kg ha-1 had been applied twice a year to the affected fields for 10 years. Dose-response tests were conducted, using 6- and 9-week-old plants that had received repeated exposure to paraquat and those that had no history of paraquat application. The estimated ED50(paraquat dose required to reduce shoot fresh weight by 50%) of both biotypes was lower for the 6-week-old as compared to the 9-week-old plants. Furthermore, the ED50 of resistant (R) biotypes was approximately three times higher than that of the susceptible (S) biotype for both the growth stages studied.


Plant Protection Quarterly (2001) 16 (1) 44-46.