The Influence Factors And Control Techniques Of Apple Tree Valsa Canker

Apple tree valsa canker, caused by valsa mali, is one of the main disease of the apple. Itoccurs widly in all major apple production areas in our country. As the disease occurrencedegree is related to the tree vigor, so we selected some factors such as defoliation, water stressand nutritions to determine their affects to valsa canker of apple. Besides, we did somescreening of chemicals and bio-control to the pathogen. The results as follows.1. Effects of defoliation stress on the development of lesions:4levels of defoliation(100%,75%,50%and0%defoliation, respectively) were designed It was found that thecanker sizes of4levels were12.87±0.23cm、7.08±0.13cm、6.08±0.17cm and4.56±0.08cmand the disease indexs were78.1、46.9、37.5and33.3, respectively. This result indicated thatcanker size was positively related to defoliation stress, in other words, the defoliation stresscan aggravate the development of valsa canker sizes.2. Effects of soil water content:4levels of water content, including high huminity(30.52%～33.48%), medium huminity (17.62%～21.23%), low huminity (11.25%～13.45%)and dry (≤8.0%), were designed.The result indicated that the canker sizes in the drought stress(low huminity and dry) were significantly larger than normal water (high huminity andmedium huminity) condition. Therefore, the soil water stress can aggravate the developmentof valsa canker sizes.3. Effects of nitrogen, potash, humic acid fertilizers: Different amount of nitrogen,potassium and humic acid fertilizers were used on the soil and leaves of apple trees. Theresults showed that the canker size and apple leaf K content has significant negativecorrelation (R2=0.72, P<0.05), and has significant positive correlation with N/K ratio.4. Effects of bio-control bacteria on apple tree valsa canker:4bacterial strains screenedshowed inhibeted effects to Valsa canker in vitro, and some protective effects on detachedbranches.5. Effects of chemicals: the effects to Valsa canker were measured to the fungicide(Coumoxystrobin), chemical agents (Humic acid, Calcium Chloride and Calcium Nitrate),and plant growth regulator (Thidiazuron). It indicated that Coumoxystrobin showed higher inhibition activity than others both in vitro and in field.