Polymorphism-Dependent\nHerbicidal Activity of Pyraquinate

Manipulation\nof solid states is a promising method to\nenhance the\nperformance of contact insecticides. However, its applicability to\nherbicides, which control weeds instead of insects, remains unknown.\nRealizing that herbicides exist as microcrystals on the leaf after\napplication, we are prompted to investigate the polymorphic landscape\nof the same herbicides with the purpose of boosting herbicidal performance.\nHerein, we report for the first time that the bioactivity of herbicides\nis highly dependent on polymorphism, using a newly developed herbicide\npyraquinate as a model substance. Five novel polymorphs of pyraquinate\nwere discovered. Their crystal structures, thermodynamic stabilities,\nand solubilities were evaluated. Bioassays in greenhouse and field\ntrials show that the newly developed metastable Form II is significantly\nmore effective than commercialized Form I against resistant barnyard\ngrass (Echinochloa crusgalli). Moreover,\nForm II exhibits significant kinetic stability in both water- and\noil-based suspension concentrates, promising its practical application.\nThis work emphasizes the necessity of polymorphism investigation for\nthe development of herbicide products and highlights the great potential\nof crystal engineering to enhance herbicidal efficacy.