The Occurrence And Fungicides Screening Of Grape Downy Mildew In Hengyan

Grape downy mildew is one of the most important diseases of grapes, was caused by Plasmopara viticola, mainly harmed leaves, shoots and other organizations of higher incidence, thus lower the grape's quality and production. The method to control grape downy mildew was using chemical, but long-term continuous use of chemicals will cause the drug resistance of Plasmopare viticola. This study surveys Hengyang area's grape downy mildew occurrence situation and to analyze the impact of weather factors on grape downy mildew damage occurred, the establishment of disease epidemics prediction model. By testing the resistance of different varieties of grape to Plasmopara viticola to select the test variety. Using leaf disc method to test the toxicity of five fungicides and azoxystrobin, dimethomorph mixtures to Plasmopare viticola, to find the efficiency ratio to provide the basis for production use, and the field experiment of screening chemical.(1) The investigation of grape downy mildew in eight vineyards in Hengyang was conducted, and the results showed that the incidence of grape downy mildew was different, which was in different varieties and different cultivation conditions. The phenomenon shows that planting conditions and grape downy mildew has some relevance. The control effect of rain shelter cultivation of grape downy mildew was compared to open-air cultivation mode was significantly enhanced, and disease resistant ability of the Euro-American hybrid grape varieties than Eurasian hybrids.(2) The grape caused by Plasmopare viticola was investigated in Hengyang City, Hunan Province in 2013,2014,2015 and the influence of the relevant meteorological factors on the occurrence of disease was analyzed based on investigative data. The results showed that the grape downy mildew occur in 3-29? and the more serious disease occurrence is in the range of 20 to 25?. The disease will be occurred when the relative humidity reaches 65%, continuous rainfall to downy mildew epidemic has played a significant role. The region grape downy mildew prediction model was established by analyzing the influence of meteorological factors on grape downy mildew in the area.(3) Using leaf disc method to test the grape's varieties of Hutai No.8, Vitoria, Drunk Jinxiang, Xiahei, Vitis davidiifoex. It was found that the disease resistance of grape downy mildew was not the same. The disease index of Hutai No.8, Vitoria, Drunk Jinxiang, Xiahei, Vitis davidiifoex were respectively:45.56,31.67,29.63,19.81,10.37, the highest disease index is Hutai No.8, which is the most susceptible.(4) In order to screen more effective fungicides against grape downy mildew, by using leaf disc method, the toxicity of mancozed, chlorothalonil, metalaxyl, azoxystrobin, dimethomorph and the mixture of azoxystrobin, dimethomorph were test against Plasmopare viticola. The result showed that the EC50 of 95% azoxystrobin,98% dimethomorph and their five ratio (1:1,1:2,2:1,1:4,4:1) was respectively 7.9003,1.7656,1.454,1.685,1.0117, 1.9688,3.2009 ?g/mL. The mixtures of azoxystrobin with dimethomorph at ratio of 2:1, it had very strong inhibiting effect on Plasmopare viticola.(5) Through field test,50% dimethomorph-azoxystrobin acetate suspension agent of grape downy mildew control effect better than the single agent control effect, especially to dilution the 50% dimethomorph-azoxystrobin at 2000-1500times is more better.