Bamboo tar as a novel fungicide: its chemical components, laboratory evaluation, and field efficacy against false smut and sheath blight of rice, and powdery mildew and Fusarium wilt of cucumber

The application of agricultural and forest residues can benefit the environment and the economy; however, they also generate a large amount of by-products. In this study, bamboo tar (BT), a waste product of bamboo charcoal production, was dissolved in natural ethanol and the surfactant alkyl glucoside to manufacture a 50% (wt/wt) BT emulsifiable concentrate (BTEC) biopesticide. BTEC was screened for fungicidal activity against pathogens. The greatest activity was seen against Ustilaginoidea virens with an EC50 (half-maximal effective concentration) value of 6 mg/L. Four phytopathogenic fungi, Podosphaera xanthii, Rhizoctonia solani, Fusarium oxysporum, and Botrytis cinerea, showed EC50 values of 2- or 4-ethylphenol > 2- or 4-methylphenol > phenol > 4-ethylguaiacol > dimethoxyphenol > 4-methylguaiacol > 4-propenyl-2,6-dimethoxyphenol > 2,4-dimethylphenol. Some of the phenolic compounds identified from the tar might be fungicidally active components. BT is a biochar waste, which has potential as a biofungicide and has promise in organic agriculture. The value of this tar may not be due to any fundamental physical differences from other synthetic fungicides, but rather due to reduced production expenses and more efficient utilization of waste products.