LITTLESEED CANARYGRASS (PHALARIS MINOR) RESISTANCE TO ISOPROTURON IN INDIA

The response of littleseed canarygrass biotypes to isoproturon, pendim ethalin, and diclofop-methyl was evaluated in India, in pot studies an d the field during the winters of 1991 to 1999 and 1992 to 1993. Some biotypes of littleseed canarygrass were resistant to isoproturon but c ross-resistance to pendimethalin and diclofop-methyl was not confirmed . The resistant biotype required a higher dose of diclofop-methyl than the susceptible biotype. Variations in the response of littleseed can arygrass biotypes were not due to isoproturon formulation, Resistant b iotypes required 2 to 8 times more isoproturon than a susceptible biot ype for the same level of control. Diclofop-methyl at 1.0 kg ai/ha app lied at the 2- to 3-leaf stage of littleseed canarygrass in pot experi ments and PRE pendimethalin at 1.5 kg ai/ha in field trials controlled resistant biotypes. Field surveys of the affected areas revealed that resistance in littleseed canarygrass is more prevalent in rice-wheat rotations compared to other crop sequences. Control of littleseed cana rygrass with isoproturon dropped from 78 to 21% from 1990 to 1993.