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Greenhouse tests showed that 0.2% camptothecin emulsifiable concentrate (EC) has strong contact toxicity to three agricultural pests, with LC50 and LC90 values of 0.1-0.6 and 0.4-5.0 mg liter(-1), respectively. The descending order of susceptibility was Nilaparvata lugens (Ståhl) > Brevicoryne brassicae (L.) > Chilo suppressalis (Walker). Field tests showed that the corrected mortality of B. brassicae and N. lugens was 94.6 and 69.1%, respectively, which was not significantly different from that with 10% imidacloprid WP at 98.4 and 63.4%, respectively. The corrected mortality of C. suppressalis was 85.8%, which was not significantly different from that with 5% Regent SC at 93.0%. Camptothecin EC showed no acute oral toxicity to the mouse (LD50 > 5000 mg/kg) nor acute dermal toxicity (LD50 > 2000 mg/kg).

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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 < 60 mg/L. Greenhouse tests in vivo showed 2,000 mg/L BTEC had a 78.4% protective effect against U. virens, and replicated treatments had an 80.6% protective effect. In addition, replicated two-year field trials were conducted in two geographical locations with four plant diseases; namely, false smut (U. virens), rice sheath blight (Thanatephorus cucumeris (Frank) Donk), cucumber powdery mildew (P. xanthii) , and cucumber Fusarium wilt (F. oxysporum). Results showed that 1,000–2,000 mg/L BTEC significantly inhibited these diseases. GC-MS analysis showed that the total phenolic mass fraction of two BT samples were 45.39% and 48.26%. Eleven components were detected and their percentage content was the following order (from high to low): 2,6-dimethoxyphenol > 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.

No abstract