DISEASES OF FRUIT TREES

Press, Volume XC, Issue 27404, 17 July 1954, Page 5

DISEASES OF FRUIT TREES

RESEARCH INTO VIRUSES Viruses are responsible for both Moorpark mottle of apricots and ring spot of apples (formerly known as Henderson spot). This has recently been discovered by the Fruit Research Station and the Plant Diseases Division, branches of the Department of Scientific and Industrial Research working in co-operation on fruit virus problems. This information is given in a statement issued by the department. The raising of healthy nursery stock is considered by research workers to be the most effective method of combating fruit tree virus diseases. Virus diseases of fruit trees are widespread and as yet no remedial treatment for them is known. While viruses are very quickly spread by grafting and budding with infected wood, their natural transmission by insects is relatively slow. Thus trees raised from virus-free stocks are likely to remain healthy. Since there is still no known method of curing virus diseases once they are established, the only effective method of control lies in propagating virusfree nursery stock. Accordingly efforts are being concentrated on finding healthy trees as a source of budwood and on removing diseased stock from nurseries. Considerable progress along these, lines has been made in one important i nursery. Effective control of plum mosaic has been achieved simply by removing infected cuttings from stock beds. Six years ago about one third of the cherry plum cuttings in a large nursery were infected but this season only one plant in 9000 showed infection. Since there is some eveidence that viruses restrict the growth and yield of infected trees throughout their life, a double saving is achieved by destroying stocks showing virus symptoms. The nursery is saved failures that follow attempts to bud certain varieties On to infected stocks and crop losses resulting from the establishment of diseased trees are also avoided.