A STUDY ON THE INFECTION REGULARITY AND CHEMICAL CONTROL OF APPLE BOT ROT.(BOTRYOSPHAERIA DOTHIDEA) IN YUNNAN

The canker disease initially observed on the trunks and fruits of apple trees was shown to be caused by Botryosphaeria dothidea,which was not reported previously in Yunnan,and which caused the wood cankers and fruit rot.The occurrence of the disease continued in apple trees all the year round.The fungus overwintering in diseased trunks and stems served as the primary source of infection in the following year,and the conidia produced in the next spring played most role as source of primary infection.The disease began to occur in early March in Kunming and became severe from mid-June to early July,and the peak of disease development occurred from mid-August to mid-September.The occurrence of the disease indicates that it is closely related to rainfall and temperature,particularly in April and May.In addition,it is also connected with the soil texture,water content,varieties and age of the tree.Examinations showed that resistance was different among varieties of apple to the fungus.The varieties of HuaNa-1 and Qinguan were the most resistant.The varieties of Fuji and Early McIntosh were fairly resistant,and Gold Delicious and Red Delicious were most susceptible.Experiments showed an effective control by painting 5° Bé lime sulphur and rockalum-rust mixture was the most effective fungicide against the disease for control.