Foxtail millet is one of the important minor cereal crops and is highly valued for its nutritional quality and drought tolerance. With the continuous expansion of the foxtail millet industry, the harm caused by foxtail millet blast has become increasingly severe. In this study, 53 samples of foxtail millet leaves symptomatic of foxtail millet blast were collected from a foxtail millet base in Dingxiang County, Shanxi Province, from June to October 2023. Isolation, culture and identification of the pathogen were carried out, yielding a total of 16 pure isolates, and preliminary studies on the growth inhibition and control effects of the fungus were conducted by determining the plate inhibition rate, scanning electron microscope observations and indoor potted plant experiments. The results showed that based on the morphological characteristics of the isolated strains and the combined analysis of ITS-RPB1-ACT sequences, all 16 pure isolates obtained were identified as Pyricularia oryzae. The results of the antifungal test showed that Bacillus velezensis YQH had the highest inhibition rate of 57.93% against the pathogen of foxtail millet blast; among chemical fungicides, 9% Pyraclostrobin Suspension Concentrate, 45% Prochloraz Emulsifiable Concentrate and 32.5% Difenoconazole–Azoxystrobin Suspension Concentrate had strong inhibitory effects on the fungus, with EC₅₀ values (95% confidence intervals) of 0.328 (0.262–0.400) μg·mL⁻¹, 0.848 (0.578–1.219) μg·mL⁻¹ and 0.310 (0.197–0.484) μg·mL⁻¹, respectively. The results of the potted plant experiment were in accordance with the in vitro antifungal results, and scanning electron microscopy showed that the mycelia in the treatment groups of these three chemical fungicides showed developmental deformities, breakage or surface shrinkage. In conclusion, B. velezensis YQH and the three chemical fungicides (especially 9% Pyraclostrobin Suspension Concentrate and 32.5% Difenoconazole–Azoxystrobin Suspension Concentrate) are effective candidates for controlling foxtail millet blast.

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.

Cyhalofop-butyl is a gramineous herbicide with good control effect, but it causes some damage when used in foxtail millet fields. Brassinolide (BR) is a type of plant growth hormone that can enhance the stress resistance of crops and plays a crucial role in eliminating and alleviating herbicide damage. To investigate the alleviating effect of BR on cyhalofop-butyl damage in foxtail millet, a study was conducted using Jingu 21 as the test material, combining pot experiments and field experiments. All test treatments were sprayed with cyhalofop-butyl at a concentration of 67.5 g a.i./ha. Three BR spraying times were set: the same day as cyhalofop-butyl spraying (D1), one day later (D2), and three days later (D3). Four BR concentrations were set—0 mg/L (C0), 0.05 mg/L (C1), 0.1 mg/L (C2), and 0.2 mg/L (C3)—resulting in a total of 12 treatments. The results showed that after BR spraying, all agronomic trait indicators of Jingu 21 in both pot and field experiments were alleviated. Compared with the control treatment, the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) increased to varying degrees, the malondialdehyde (MDA) content decreased, and the drug damage level was alleviated to different extents. In addition, spraying BR can increase the yield of Jingu 21 under cyhalofop-butyl herbicide damage. The results of all indicators indicated that spraying BR one day after cyhalofop-butyl spraying had the best effect. Therefore, spraying BR at a concentration of 0.1 mg/L can effectively alleviate the damage of Jingu 21 plants. It is recommended that when using BR to alleviate damage in foxtail millet, the application should be spaced one day apart from the herbicide spraying.

Giant foxtail is a common weed in foxtail millet fields, and continuous cropping of foxtail millet increases its occurrence. Rotating foxtail millet with sorghum is a major practice in the dry farming regions of northern China. Given this situation, this study combined Petri dish germination tests with pot experiments to clarify the allelopathic effects of water extracts from different sorghum parts on giant foxtail. Distilled water (SCK) was used as the control, and treatments included stock solution (S1), as well as 10× dilution (S2), 50× dilution (S3), and 100× dilution (S4) of water extracts prepared from sorghum roots, stems, leaves, and rhizosphere soil. The results showed that water extracts from all sorghum parts exhibited promotion of giant foxtail seed germination at higher dilutions and inhibition at lower dilutions. The S3 treatment of rhizosphere soil extract achieved a germination rate of 62.22%, which was significantly higher than that of the SCK by 40.00%. The germination energy of root extract S1 was only 4.00%, which was significantly lower than that of the SCK by 86.67%. The S3 treatment showed the strongest allelopathic promotion effect. All dilution treatments promoted the plant height, stem diameter, and above ground fresh and dry weight of giant Foxtail, and these effects increased initially and then stabilized over time. The root extract exhibited higher allelopathic activity than the other extracts. The activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) first increased and then decreased as the dilution factor increased, while the S1 treatment inhibited enzyme activities and caused an imbalance in the antioxidant system. Sorghum root water extract had a significant effect on CAT activity in giant foxtail, with an increase of 98.82% under the S3 treatment compared with the SCK at 40 d. Malondialdehyde (MDA) content increased with decreasing dilution factor, and the undiluted extract induced membrane lipid peroxidation damage. In conclusion, the allelopathic effects of sorghum extracts on giant foxtail were closely related to the dilution level. Higher dilutions activated the antioxidant defense system and promoted growth, while lower dilutions disrupted enzyme system balance and exacerbated membrane damage. These findings provide basic data and theoretical support for the development and utilization of sorghum allelochemicals and for the green control of giant foxtail.

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.

Sethoxydim, a cyclohexanedione herbicide inhibiting acetyl-CoA carboxylase (ACCase), is widely used for post-emergence control of graminaceous weeds in foxtail millet (Setaria italica (L.) Beauv.) fields. This study investigated under field conditions the effects of sethoxydim on root morphology and rhizosphere microecology using two cultivars with contrasting tolerance: the relatively tolerant hybrid Zhangzagu 10 and the relatively sensitive conventional Zhonggu 19. Previous studies on sethoxydim in foxtail millet have focused primarily on shoot physiology, whereas integrated assessments of root morphology, soil enzyme activity, and rhizosphere microbiome remain scarce. Sethoxydim was applied at 112.5, 225.0, or 337.5 g a.i./hm² (0.5×, 1×, and 1.5× the recommended dose), with water as control. Root morphology and rhizosphere enzyme activities were measured at 0, 7, 14, 21, and 28 days after application, and bacterial and fungal communities were analyzed by high-throughput sequencing. Sethoxydim inhibited root growth in both cultivars, but Zhonggu 19 was consistently more sensitive. At 337.5 g a.i./hm², root length, surface area, diameter, and volume were markedly reduced in Zhonggu 19, whereas Zhangzagu 10 showed milder inhibition and even slight stimulation at lower doses. Rhizosphere urease, sucrase, and catalase activities initially decreased then recovered. Sethoxydim altered α-diversity and community structure of rhizosphere bacteria and fungi. These preliminary findings suggest that sethoxydim may be tentatively applied at or below the recommended dose (≤225.0 g a.i./hm²) under similar field conditions, particularly for tolerant cultivars such as Zhangzagu 10, though confirmation through multi-year trials is required.