Characteristic and Management of Sulfonylurea-Resistant Scirpus planiculmis Confirmed in Reclaimed Paddy Fields, Korea

A suspected biotype of Scirpus planiculmis (S. planiculmis)to be resistant to sulfonylurea (SU) herbicides was identified in Seosan reclaimed paddy fields in Korea. The fields have been cultivated for mono-cultural rice production with wet-direct seeding method and continuously treated with SU-based herbicide mixtures for thirteen years since 1990. The apparent SU resistance observed in S. planiculmis was completely confirmed in greenhouse tests. The GR50 values of 6 SU herbicides for SU-resistant biotypes were 47 to 100 times higher than those for SU-susceptible biotypes. The I50 values of pyrazosulfuron-ethyl to acetolactate synthase (ALS) extracted from SU-resistant and -susceptible S. planiculmis were 409 nM and 0.8 nM, respectively. The I50 value of the resistant biotype was 511 times higher than that of the susceptible biotype. The germination and growth rate from corm and seed of SU-resistant S. planiculmis under growth chamber were high with the rise of temperature, and the degrees of those were greater in corm than seed. In the interspecific competition according to SU-resistant S. planiculmi density in constant the rice 3 plants under wet direct seeded rice, the growth of rice decreased with the increase of S. planiculmi density and significant differences were from 6 plants of S. planiculmi density. Several herbicides having different mechanism of action from SU herbicides, such as benzobicyclone and HAR had excellent controlling effects on the SU-resistant S. planiculmi in the pot and paddy rice field experiment.