Weeds compete with rice for nutrition and other resources, causing yield and economic losses. Herbicides serve as an essential tool for weed management in rice. However, with repeated use of herbicides with the same site of action (SOA), herbicide-resistant weed biotypes have evolved in rice production systems in the U.S. Limited information was available on the herbicide resistance status in Texas rice fields. A paper-based survey was conducted in 2016-17 among the stakeholders to understand their perspective on herbicide use and herbicide-resistance issues. Further, field surveys were carried out to map the distribution of herbicide-resistant Echinochloa spp. and weey rice (Oryza sativa). Fifty-four Echinochloa populations collected from the surveys were planted in a field to understand the evolutionary changes in their morphological and physiological characteristics. Field surveys indicated that junglerice (E. colona), weedy rice, and Nealley's sprangletop were the dominant weed species in Texas rice production. In general, barnyardgrass and rough barnyardgrass ecotypes were tallest and exhibited wider flag leaves and longer panicles when compared with the junglerice. Plant height, flag leaf length, seed shattering and seed germination were the highest contributing factors to the diversity of Echinochloa ecotypes. The qualitative trait, stem color was highly correlated (0.81) with canopy structure. The Echinochloa ecotypes (e.g. E. colona) with purple stem color had open geometry with shorter stature compared with other ecotypes (e.g. E. cruss-galli and E. muricata) with green stem. Surveyed populations (Echinochloa spp.) exhibited resistance to imazethapyr, quinclorac, fenoxaprop and propanil, and some populations even exhibited multiple- resisance to more than one herbicide SOAs. However, no significant association was observed between multiple resistance and 13 morpho-physiological traits of characterized Echinochloa ppopulations. The findings of this study can help in identifying and characterization of Echinochloa spp. in general and devising an alternate herbicide program to control herbicide-resistant weeds.
