Abstract
Paraquat resistant plants of Erigeron philadelphicus L. were detected in mulberry fields located on the riverside land of the Arakawa river in Fukiage, Saitama Prefecture, where paraquat had been applied 2 or 3 times annually during the preceding 8-11 years. These paraquat resistant plants were killed by generally recommended dosages of bentazon, glyphosate and MCPA, and were considered non-resistant to these herbicides. It would seem that the resistant plants appeared approximately 5-6 years after paraquat was introduced to these fields. It may be concluded that, for control of Erigeron philadelphicus which has developed resistance to paraquat, the concentration of paraquat should be maintained at a level 50 to 100 times higher than that for common susceptible plants.
