Efficacy and Safety of Soil-sealed Herbicides in Next Generation Dryland Rice Fields

Purpose This study aimed to investigate the efficacy of pre-emergence soil treatments with herbicides including butachlor, pendimethalin, and penoxsulam with clomazone, bensulfuron-methyl, and pyrazosulfuron-ethyl against major weeds in next generation dryland rice (NGDR) fields in Yunnan Province, evaluating their safety on rice growth, and to screen the optimal herbicide formulation suitable for soil sealing treatment in NGDR fields.

Methods The field efficacy trials were conducted to comprehensively evaluate the safety of the aforementioned six herbicides on the plant height, biomass, and other indicators of NGDR variety Dianheyou 615, as well as their control efficacy against five weeds (Digitaria sanguinalis, Eleusine indica, Bidens pilosa, Ageratum conyzoides, and Galinsoga quadriradiata).

Results At 14 days after application (DAA), rice leaves yellowing and plant stunting were observed in treatments with penoxsulam and its mixtures; slight recovery occurred at 28 DAA, but phytotoxicity symptoms remained. After 14 days of treatment with a mixture of clomazone, the rice leaves bleaching was observed, but leaves recovered by 28 DAA without affecting rice growth. Other treatments were safe to rice. The plant control efficacy of single applications of butachlor and pendimethalin reached 63.95% and 76.89% at 28 DAA, respectively; and their mixtures with bensulfuron-methyl or pyrazosulfuron-ethyl significantly increased weed control efficacy. Compared with bensulfuron-methyl, pyrazosulfuron-ethyl provided excellent control against B. pilosa.

Conclusion Due to phytotoxicity risks, it is not recommended to use penoxsulam and clomazone as soil treatment agents. For weed control in NGDR fields, 450 g/L pendimethalin or 60% butachlor mixed with 15% pyrazosulfuron-ethyl is suitable. In fields with low B. pilosa infestation, mixtures with bensulfuron-methyl can also be used for soil-sealed.