Fungicide and insecticide activity of Justicia procumbens extracts

Justicia procumbens is traditional Chinese medicine herb. To confirm fungicidal and insecticidal activity of J. procumbens extracts, methanol, chloroform, acetone, ethyl acetate and hexane extracts were obtained from J. procumbens by the combined method of cold-soaking and ultrasonic extraction. Extract inhibitory effects were studied using the inhibition zone method involving five species of plant pathogenic fungus-Colletotrichum gloeosprioides, Phomopsis asparagi, Pyricularia grisea, Fusarium graminearum and Botrytis cinerea. Methanol extract toxicity against four species of plant pathogenic fungus and bacteria (C. gloeosprioides, P. asparagi, B. cinerea and Xanthomonas campestris) and three species of insects (Aedes albopictus, Musca domestica and Pieris rapae) were also assayed. Results showed that 8 mg?mL^-1 extracts of J. procumbens with different polar solvents had some inhibitory effects on five species of plant pathogenic fungus. The inhibition rates of methanol extract against C. gloeosprioides, P. asparagi and B. cinerea were over 50%. Methanol extract from J. procumbens had better fungicidal and insecticidal activity. EC₅₀ of methanol extract against mycelium growth of C. gloeosprioides, P. asparagi and B. cinerea were 5.94 mg?mL^-1, 4.61 mg?mL^-1 and 5.27 mg?mL^-1, respectively. The corresponding EC₉₀ were 63.69 mg?mL^-1, 58.01 mg?mL^-1 and 54.57 mg?mL ^-1, respectively. Methanol extract at 0.25~1.00 mg?mL^-1 showed strong inhibitory activity against X. campestris. The resultant extract at 0.125 mg?mL^-1 showed moderate inhibitory activity. Methanol extract MIC was 0.062 5 mg?mL^-1. Methanol extract LC₅₀ against A. albopictus, M. domestica and P. rapae were 0.195 8 mg?mL^-1, 0.351 4 mg?mL^-1 and 0.287 7 mg?mL^-1, respectively. The corresponding EC95 were 0.988 4 mg?mL^-1, 3.053 2 mg?mL^-1 and 2.584 4 mg?mL^-1, respectively. This suggested that J. procumbens extracts had better application prospects as a biological pesticide in agricultural production.