Synergistic effect of composite microbial bioactive metabolites in the control of rice diseases and pest insects under reduced-dosage chemical pesticide application

To advance green strategies for rice protection, this study developed a microbial bioactive formulation (TMB) from Trichoderma asperellum, Metarhizium anisopliae, and Bacillus subtilis metabolites, demonstrating its synergy with chemical pesticides at reduced doses. In vitro antifungal assays determined the optimal TMB ratio as 1:1:1 (v/v/v), with inhibition rates of 85.3% and 67.4% against Curvularia plantarum and Fusarium fujikuroi, which is significantly higher than those of single-strain metabolites. The biochar-based TMB coating agent, when applied as a seed treatment, suppressed rice sheath blight (Rhizoctonia solani) by 75.56% and significantly improved seed germination rates under co-infection by C. plantarum and F.fujikuroi (p < 0.05). The co-application of TMB and 30%–50% reduced dosage of 75% trifloxystrobin · tebuconazole resulted in higher inhibition rate against C. plantarum than equivalent-dose chemical pesticides alone , reaching a level comparable to that of full-dose chemical pesticides. Field trials demonstrated that TMB combined with 30%–40% reduced chemical pesticides achieved excellent synergistic effects against rice sheath blight, rice spikelet rot , rice grain black spot, and rice pest insects such as brown planthopper (Nilaparvata lugens), and rice leaf roller (Cnaphalocrocis medinalis), with control efficacy generally reaching or surpassing full-dose chemical treatments. Specifically, TMB combined with a 40% reduction in chemicals achieved more than 60% control efficacy against N. lugens and 80% against C. medinalis; TMB combined with a 30% reduction in tebuconazole · azoxystrobin doubled the control efficacy against rice kernel black spot in terms of reducing diseased incidence compared to full-dose chemicals, representing an 87% improvement over conventional applications. This study confirms that the synergistic use of TMB with reduced chemical pesticides provides a feasible and effective strategy for high-efficiency green control of rice diseases and pests while significantly reducing by 30% in chemical inputs.