Grass damage has become an important factor restricting foxtail millet production; chemical weeding can help resolve this issue. However, special herbicides in foxtail millet fields are lacking. Penoxsulam has a broad weed control spectrum and a good control effect. In this project, Jingu 21 was used as the test material, and five different concentrations of penoxsulam were used for spraying test in the three–five leaf stage. In this experiment, the effects on the growth of foxtail millet were discussed by measuring the agronomic characters and antioxidant capacity of foxtail millet after spraying penoxsulam. The results showed that: (1) penoxsulam is particularly effective in controlling Amaranthus retroflexus L. (A. retroflexus) and Echinochloa crus-galli (L.) Beauv. (E. crus-galli), but is ineffective in controlling Chenopodium album L. (C. album) and Digitaria sanguinalis (L.) Scop. (D. sanguinalis); (2) the stem diameter, fresh weight, and dry weight of the above-ground parts decreased with the increase in spraying amount; (3) as the spraying dosage increased, the superoxide (SOD), peroxidase (POD), and catalase (CAT) activities in the foxtail millet initially increased and subsequently decreased; the malonaldehyde (MDA) content increased. Our experiment found that 1/2X and 1X spraying dosages had certain application value in controlling gramineous weeds in foxtail millet field. Other spraying dosages are not recommended as they may harm the crops. Our findings provide reference for identifying new herbicides in the foxtail millet field.

Foxtail millet planting has a long history and profound role in agricultural civilization. However, weeds have become one of the obstacles restricting the development of the foxtail millet industry. Penoxsulam, as an early post-emergence herbicide for controlling gramineous weeds in paddy fields, is effective for some broadleaf weeds. In this study, six different doses (CK, 0.5X, 1X, 2X, 3X, 4X) of penoxsulam were sprayed at the 3–5 leaf stage of the conventional variety Jingu 21 to study its effect on the growth and development of foxtail millet, in order to screen out the appropriate spraying concentration. The main results are as follows: Within 15 days after spraying penoxsulam, the plant height and leaf area of foxtail millet decreased with the increase in spraying dose, and gradually recovered 15–25 days after spraying, but there were still significant differences compared with CK. The photosynthetic pigment content, net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), the maximum photochemical efficiency (Fv/Fm), photosynthetic system II actual photochemical efficiency (Y(II)), and photochemical quenching coefficient (qP) of foxtail millet decreased with an increase in the penoxsulam spraying dose, while the intercellular CO₂ concentration (Ci) and non-photochemical quenching coefficient (NPQ) showed an upward trend. There was almost no significant difference in each index between the spraying dose of 0.5X and 1X and CK, but the photosynthesis of foxtail millet leaves was still significantly inhibited under a spraying dose of 3X and 4X. Penoxsulam had certain growth-inhibiting effects on Echinochloa crus-galli (L.) Beauv. (E. crus-galli), Digitaria sanguinalis (L.) Scop. (D. sanguinalis), Chenopodium album L. (C. album), and Amaranthus retroflexus L. (A. retroflexus) which increased as the spraying dosage increased. Our study found that spraying dose groups of 0.5X and 1X penoxsulam were safe for foxtail millet growth and could be used to control gramineous weeds in fields. Other spraying doses are not recommended in the field due to their serious phytotoxicity to foxtail millet, which provides a new measure for weed control in foxtail millet fields.

Foxtail millet is a characteristic miscellaneous grain crop with many benefits in current agricultural production and is crucial in the adjustment of the planting structure and the sustainable development of dry farming. However, the harmful effects of weeds have become a critical challenge, restricting the modern production of foxtail millet. The effect of penoxsulam on the chlorophyll metabolism pathway of foxtail millet and its physiological mechanism was studied. Spraying penoxsulam on foxtail millet leaves significantly reduced the content of chlorophyll synthesis precursors (5-aminolevulinic acid (ALA), Porphobilinogen (PBG), Protoporphyrin IX (ProtoIX), Mg-protoporphyrin IX (Mg-ProtoIX), and Protochlorophyllide (Pchlide)). Moreover, the activities of key synthetic enzymes (magnesium chelatase (MgCh) decreased compared to control, while the activities of degrading enzymes (pheophorbide a oxygenase (PAO) and pheophytinase activities (PPH) increased significantly. The study revealed the mechanism of penoxsulam inducing crop phytotoxicity by interfering with the dynamic balance of chlorophyll metabolism, which provided a theoretical basis for the scientific application of herbicides and the study of foxtail millet drug resistance.

The specific objectives include three points: (1) to clarify the dynamic change laws of the contents of three key endogenous hormones, namely, indole-3-acetic acid (IAA), gibberellin (GA), and abscisic acid (ABA), in foxtail millet leaves after penoxsulam treatment, and their correlations with drug dose and treatment time; (2) to analyze the effects of different doses of penoxsulam on the antioxidant system of foxtail millet, specifically including the change characteristics of hydrogen peroxide (H₂O₂), superoxide anion (O₂⁻), reduced glutathione (GSH) content, and cell membrane permeability (MP); and (3) to reveal the correlation between endogenous hormone changes and antioxidant system indicators through correlation analysis so as to provide a direct experimental basis for the screening of safe doses of penoxsulam application in foxtail millet fields and the research on the herbicide stress resistance mechanism of foxtail millet. Using Jingu 21 as the test material, four penoxsulam dose levels were set through pot and field experiments. The changes in endogenous hormone content, antioxidant system indexes, and phenotypic indicators of foxtail millet were determined at different periods after treatment, and the correlation between endogenous hormones and antioxidant systems was analyzed. Compared with the control (P₀), the contents of IAA and GA in foxtail millet showed a “first increasing and then decreasing” trend, while the content of ABA showed a continuous increasing trend. With the increase in penoxsulam concentration, the contents of H₂O₂, O₂⁻, GSH, and MP in foxtail millet gradually increased. A correlation analysis showed that there was a significant correlation between leaf endogenous hormones and the defense capacity of the antioxidant system. After penoxsulam treatment, foxtail millet leaves showed dynamic changes of “first increasing and then decreasing” in IAA and GA contents, and a continuous increase in ABA contents. At the same time, H₂O₂, O₂⁻, GSH content, and MP increased significantly with the increase in the drug dose. It is speculated that foxtail millet may indirectly regulate the defense ability of the antioxidant system by regulating the content of endogenous hormones to alleviate the damage of herbicide stress.

Weed infestation severely impairs foxtail millet growth, while new herbicide development faces long cycles and high costs. This study examined cyhalofop-butyl (effective against Echinochloa crus-galli (E. crus-galli) in paddy fields) to assess its effects on agronomic traits, antioxidant enzyme activities, malondialdehyde (MDA) content of Jingu 21, and weed control efficacy in foxtail millet fields, aiming to screen safe, effective concentrations. Results showed that sole cyhalofop-butyl inhibited foxtail millet growth: high-dose treatments retained significant agronomic trait inhibition 30 days post-spray. Early post-spray, superoxide dismutase (SOD) and peroxidase (POD) activities showed a “first increase then decrease” pattern, catalase (CAT) a “first decrease then increase” trend, and MDA content rose; index differences from the water control narrowed over time, though 90 g a.i./hm² still caused higher leaf SOD activity and MDA content in later stages. For weed control, cyhalofop-butyl effectively controlled E. crus-galli (control effect “first increase then decrease,” 90 g a.i./hm² optimal) and Digitaria sanguinalis (D. sanguinalis) (control effect rising over time) in foxtail millet fields. On the whole, 22.5 g a.i./hm² and 45 g a.i./hm² of cyhalofop-butyl are safe for Jingu 21, and 67.5 g a.i./hm² is also a safe concentration, so 45–67.5 g a.i./hm² can be preferred for comprehensive weed control.