Study And Screening On Plant Extracts Against Powdery Mildew Of Cucumber

The protective and curative effects of 102 species of plant extracts made by 80% ethanol were tested against powdery mildew of cucumber in vive. 11 species of the extracts showed strong preventive activity and 2 species showed strong curative control. They significantly reduced the severity of powdery mildew compared to control plants and their efficacy reached to the same significant level as chemical fungicides (Triademefon and Myclooutanil) at a concentration of 2%. TS-86 and TS-109 were selected to be further studied according to their high efficacy, low cost and easy making characters. Their fungitoxity to powdery mildew were tested. The results demonstrated that Ec50 of TS-86 was 688.68 times and Ec90 was 386.53 times. While the Ec50 of TS-109 was 1398.50 times and Ec90 was 1051.21 times.The protective activities of TS-86 and TS-109 were tested after being treated at different temperatures, illumination and pH values. Results showed that the efficacy of TS-86 was not stable at different temperatures and pH values. The efficacy was better in pH6~8 and the best after treated at 100'C for one hour. But its light stability is very good. At the same time, the efficacy of TS-109 was very stable at different temperature (from -20癈 to 80癈), or pH values (from 2 to 10) and its efficacy enhanced with the length of the illuminated time (the efficacy of TS-109 which was illuminated 0 h and 72 h were 90.20% and 97.96%, respectively).The duration of the protective efficacy of TS-86 and TS-109 were tested by spraying these extracts at a concentration of 1% one to six days ahead of inoculation. In addition, TS-86 extract treated in 100癈 for an hour was added. Great difference was found between the treated and untreated TS-86 extract at 100癈. The effectivity could reach for up to 6 days with high temperature treated TS-86 at a concentration of480.2% and 5 days with untreated TS-86 at concentration of 1 %. The protective duration of TS-109 was up to 6 days at least with the efficacy over 90%.Inhibitory effects of TS-86 and TS-109 to other fungi were tested by means of mycelial growth inhibition method. The inhibitory spectrum of TS-86 was more extensive than TS-109. TS-86 inhibited the mycelial growth of Botrytis cinerea, Cochliobolus sativus, Exserohilun turcicum and Verticillium dahlias up to 90% at 100 times dilution. While TS-109 only inhibited C. sativus and E. turcicum up to 80% or so at the same concentration.The efficiencies of TS-86 and TS-109 extracts from different shaking time were asle tested. The results showed the appropriate shaking time of TS-86 and TS-109 was 7 d and 2 d, respetctively.The standard samples of Chrysophanol and Rhein were used for comparison, by HPLC. Results showed that Chrysophanol was one of the active fractions of TS-109.