Herbicide resistance to pyrazosulfuron-ethyl of gooseweed (Sphenoclea zeylanica Gaertn.) in Thai paddy fields

Abstract

Gooseweed (Sphenoclea zeylanica Gaertn.) is a problematic weed in paddy fields. Most farmers use herbicides to control gooseweed such as acetolactate synthase enzyme (ALS) inhibiting herbicides and auxin mimics herbicides. The farmers reported that pyrazosulfuron-ethyl cannot control suspected resistant gooseweed populations in the rice field. This study aimed to survey the occurrence of pyrazosulfuron-ethyl resistant gooseweed in 100 populations across Thai rice fields, investigate the level of pyrazosulfuron-ethyl resistance, and evaluate alternative chemical control of pyrazosulfuron-ethyl resistant gooseweed populations. Pyrazosulfuron-ethyl-resistant gooseweed was identified in 52 rice fields (52%). Across different regions, the cluster of pyrazosulfuron-ethyl-resistant was greater observed in Central region of Thailand than the North and the Northeast areas. GR₅₀ based on plant dry weight for pyrazosulfuron-ethyl-resistant from Ang Thong (P22) and Phra Nakhon Si Ayutthaya (P43) provinces were 33.36 and 19.18 g ai/rai which were 111.2 and 63.93 times greater than for the susceptible population from Surin province (P54; GR₅₀ = 0.3 g ai/rai), respectively. Cross resistance to other ALS-inhibiting herbicides was found to bispyribac-sodium in P22 and P43 populations. However, propanil, carfentrazone-ethyl, and 2,4-D provided effective control of the two pyrazosulfuron-ethyl-resistant gooseweed populations. It could possibly suggest these herbicides in combination with other non-chemical weed control methods to manage pyrazosulfuron-ethyl-resistant gooseweed populations in rice fields.