Studies On Occurrence Regularity And Chemical Control Of Walnut Anthracnose

Walnut (Juglans regia L.) is significant ‘woody grain’ strategic species. Walnutanthracnose caused by Colletotrichum gloeosporioides is the serious diseases of walnutorchards in Shandong Province. In this study, based on the investigation of overwinteringplaces and states of C. gloeosporioides and walnut anthracnose disease dynamics in ShandongProvince, the occurrence regularity of walnut anthracnose in Shandong Province was studied.The aboratory toxicity of eight fungicides to walnut anthracnose pathogen was determinedwith both mycelial growth rate test and conidial germination assay. The toxicity of prochlorazand tebuconazole to four selected strains of C. gloeosporioides under different temperatureswere determined，and the sensitivity to prochloraz and tebuconazole of all seventeen strainstested were screened with mycelial growth rate test. Meanwhile the protective and curativeeffects of prochloraz and tebuconazole were evaluated at the same time. Following theoccurrence regularity of walnut anthracnose, different fungicides compositions and timecombinations of field trials to developing the effective chemical control programs of walnutanthracnose in Shandong Province. The study results are as following.1.Occurrence regularity of walnut anthracnose in Shandong ProvinceThis study is based on national food safety standards "maximum residue limits forpesticides in food"(GB2763-2012) and the agriculture industry standard "green guidelines forthe use of pesticides"(NY/T393-2000), selection of safe, efficient, fungicides-prochloraz,tebuconazole, iprodione, triadimefon, mancozeb, combined with walnut anthracnoseoccurrence regularity, to developing prevention measures: dormant for trunks painted white,March before budding spraying lime sulfur, prevention against pathogens overwintering; lateApril to mid-May, spraying iprodione, mancozeb and streptomycin protecting walnutanthracnose and other diseases; late June to mid-July, spraying prochloraz and triadimefon,early August sprayed tebuconazole on Walnut incidence for therapeutic controlling. Sporesdiffusion and disease dynamics, are closely related with temperature changing, withcharacteristics of continuous accumulation and explosive.2. Fungistasis of eight fungicides to C. gloeosporioidesThe higher toxicity to mycelium growth of C. gloeosporioides belonged to prochloraz,tebuconazole and triadimefon with EC50values of0.070,1.448,3.038mg/L respectively, and iprodione, mancozeb and prochloraz to conidial germination with EC50values of21.07,25.14,25.18mg/L under28℃. Carbendazim showed larger difference on both mycelium growthand conidial germination between four strains. The highest sensitivity to carbendazim of fourstrains is6814.69times to the lowest. The fungistasis of prochloraz and tebuconazole to C.gloeosporioides increased when the temperature decreased and the two fungicides showedefficiently protective and curative activities. Prochloraz, tebuconazole and iprodione could beadopted as the effective fungicides for walnut anthracnose management.3.Sensitivity of C. gloeosporioides to fungicidesSensitivity of C. gloeosporioides to fungicides showing large differences, sensitivity tofungicide from different strains also different. The highest sensitivity belong to prochlorazwith the average EC50value of0.08±0.05mg/L, the highest is the minimum8.33times;followed by tebuconazole, the average sensitivity EC50value of1.09±0.11mg/L, the highestis the minimum3.3times; the last is iprodione with the average EC50of18.06±4.91mg/L.4. Chemical control technique of walnut anthracnoseReference to the agricultural industry standard "green guidelines for the use ofpesticides"(NY/T393-2000), combined with walnut anthracnose disease patterns and efficacytrial results, the development of walnut anthracnose control measures: March to beforebudding, spraying liquid of lime sulfur for killing the overwintering pathogens; Late April tomiddle May, at the initial stage of the disease, spraying protective fungicides andstreptomycin by protecting walnut trees and preventing early diseases of walnut. Sprayingiprodione mancozeb mixed with streptomycin liquid for prevention. Late June to August is thepeak of walnut anthracnose incidence. In order to reduce the residues of each fungicide in thewalnut, blending or alternatively applying therapeutic fungicides such as prochloraz,tebuconazole and triadimefon for integrated control of walnut anthracnose. With theagricultural management, regulate the growth and enhance resistance to disease. LateSeptember to October,clearing the diseased twigs and litter layers, falling fruits, deepplowing surface soil reduce amounts of overwintering pathogen.