Balancing Crop Safety and Weed Control: Integrated Application of the Safener Metcamifen and Pretilachlor for Weedy Rice Management in Wet Direct-Seeded Rice

Wet direct-seeded rice (WDSR) is a resource-efficient cultivation system gaining global popularity, but its sustainability is severely threatened by weedy rice (Oryza sativa f. spontanea). Due to the high genetic and physiological similarities between weedy and cultivated rice, selective chemical control remains a formidable challenge. This study evaluated an integrated chemical control strategy utilizing the safener metcamifen (applied as a seed coating) to protect cultivated rice from the pre-emergence herbicide pretilachlor in a simulated WDSR system. Indoor bioassays and outdoor mock-plot trials revealed that metcamifen seed coating alone (up to 560 mg a.i. kg−1 seed) significantly promoted early seedling vigor in cultivated rice (‘Jia 67’) without exhibiting phytotoxicity. Conversely, soil application of pretilachlor at 375 g a.i. ha−1 provided effective initial herbicidal activity, suppressing weedy rice emergence to merely 7.0%. Under this severe herbicide stress, metcamifen seed coating at an effective dose of 480 mg a.i. kg−1 seed significantly mitigated phytotoxicity. However, this protection was partial; crop emergence was maintained at 63.8%, substantially preserving seedling biomass compared to the non-safened control (28.3%), but still reflecting a clear emergence penalty. We hypothesize that this moderate reduction in initial crop stand could potentially be compensated by proportionally increasing the initial seeding rate—a potential agronomic compromise that warrants future empirical validation in the field. In summary, this study provides a preliminary, controlled-environment evaluation demonstrating that the protective application of metcamifen with pretilachlor offers a potential framework for mitigating weedy rice infestations, subject to further field-scale verification.