| Summary: | In this study, rapid resistance in-season quick (RISQ) tests were developed for detecting the resistance in <i>Echinochloa</i> spp. to penoxsulam, metamifop, and quinclorac, which are widely used in rice fields to control <i>E.</i> spp. biotypes. Seedlings in 1–2 leaf stages from nine biotypes of <i>E. crusgalli</i>, <i>E. crusgalli var. zelayensis,</i> and <i>E. glabrescens,</i> with different susceptibility to the three herbicides tested, were transplanted to plates containing nutrient agar and different rates of herbicides. The survival rates were recorded at 8 days after treatment when no more new roots emerged for all the treatments. By comparing the results from RISQ tests and whole-plant pot bioassays statistically, discrimination rates could be determined to distinguish resistant plants from susceptible plants. For penoxsulam, metamifop, and quinclorac, the discrimination rates were 0.3, 0.6, and 2.4 µmol/L, respectively. Two additional biotypes of <i>E</i>. <i>crusgalli</i> collected in rice fields were used to confirm the validation of the RISQ test and the obtained results by the RISQ test were consistent with that of the whole-plant pot bioassay. Therefore, the developed RISQ test would be a possible alternative method to determine the susceptibility of <i>E</i>. spp. to certain herbicides.
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