A Study Of The Cause Of Valsa Canker And Control Techniques

China is the country which has the biggest both planting area and the total output of apple.But its yield per unit is still lower than the average level in the world,which is mostly caused by valsa canker.Valsa canker generally occurs in north China apple producing areas and causes serious harm.This disease always harms the fruit trunks and limbs,meanwhile,twigs,young trees and fruits also can be harmed.There are a variety of speculations of the causes of valsa canker although,but no test evidence was found,so no prevention countermeasures have found in the production effectives.Leaf samples were collected from Fuji orchards which are 15～25 year-old in Baishui County,Fuping County,and Yangling in Shaanxi Province,according to canker occurrence degrees and orchard management levels.Then the contents of mineral nutrient elements were analysed,and the canker occurrences were investigated.The relationships between the contents and the disease incidences and disease indexes were analyzed,and found that there are relationships between leaf K between later July and earlier August and both the disease incidences and disease indexes in the same year and next year.That feaf K is much too low could be the cause of valsa canker.Because of the outcome of the experiment,there are a couple of suggestions:K level should be increased to higher than 1.00%,while N level should be reduced and keep it at about 2.00%,keep N/K ratio at 2 or so,and keep P/K ratio at 0.18,so the tree nutrition level can be balanced,the resistance of trees can be enhanced and,the disease can be prevented.The 6 sold fungicides like benziothiazolinone were tested in dish efficacy trials,conidium germination test,and excised branches inoculation test,and then tested in a field test in Baishui County.Result:benziothiazolinone is the best,its EC50 is 11.00μg/mL,excised branch test can prove it.1.6%benziothiazolinone(made by Shaanxi xidahuate technology industrial Co.,LTD)diluted to 1/400,sprayed once in February,March,April,and May,the percentage of inhibition next year is 71.3%.The functionalities of 19 wound protectants sold were tested by seal tests in pruning wounds and scraped wounds,and then healing and control effects were surveyed in July 2011.3 best protectants were screened.The 4 homemade wound protectants were tested by wound coating,proved that 2 of them are good at wound healing and on wound expaned.The 2 are worthy popularized.