Effects of the application of herbicides mixed with safeners on weeds control efficacy and the safety to proso millet

To evaluate the effect of herbicides mixed with safeners on weeds control efficacy and the safety to proso millet (Panicum miliaceum L.) at high- and low- dosages of herbicides, Sigma broad (mesosulfuron-methyl + iodosulfuron-methyl-sodium 3.6% WG) and Quelex (halauxifen-methyl + florasulam 20% WP), were mixed with safeners, brassinolide (BR) or gibberellic acid (GA), and sprayed on the leaves and stems of ‘Yumi-2’ cultivar at three-leaf stage. Meanwhile, artificial weeding (control check 1, CK1) and tap water (control check 2, CK2) were included. The phytotoxicity index, control efficacy of weed, relative chlorophyll content, and active oxygen metabolism in leaves, shoot biomass, and seed yields were measured. The results showed that: BR eliminated the phytotoxicity of Sigma broad herbicide at low dosage, and 11.5% reduction of phytotoxicity index at high dosage; GA eliminated the phytotoxicity of low-dose Quelex herbicide and 40.9% reduction of phytotoxicity index of high-dose Quelex herbicide. However, the control effect of weed decreased 1.7%-18.0% in the treatments of herbicides and safener combinations. Application of herbicide plus safener increased the activity of superoxide dismutase (SOD) and chlorophyll content to some extent and decreased the content of malondialdehyde (MDA) significantly in proso millet leaves. Compared with the single application of herbicide, the SOD activity in the leaves of proso millet increased in the treatments of low- and high-dose Sigma broad herbicide mixed with BR at 7 d and 28 d after heading stage, and in the treatments of Quelex herbicide mixed with BR or GA at 7d after heading stage. Compared with the single application of herbicide, the shoot biomass of proso millet increased significantly in the treatments of Sigma broad herbicide mixed with BR or GA at 21-28 d after heading stage, and low-dose Quelex mixed with BR at 14 d after heading stage, and high-dose Quelex mixed with GA at 28 d after heading stage. The treatments with the mixture of herbicides and safener increased the seed yield of proso millet. The maximum yield was gained in the treatments of 600 g/hm² Sigma broad herbicide mixed with 0.015 g/hm² BR and 100 g/hm² Quelex herbicide mixed with 14.7 g/hm² GA, with 26.1% and 27.9% higher than the control of CK2, and 4.6% and 11.6% higher than the herbicide application only, respectively. The results could provide a scientific basis for the safety application of herbicides in broomcorn millet field and the use of plant growth regulators to alleviate herbicide phytotoxicity.