THE CAUSES AND SIGNIFICANCE OF DYING APPLE TREE BRANCH AND CROWNS 



George N. Agrios 

 Department of Entomology and Plant Pathology 



In almost every apple orchard, some trees have a few branches with 

 sparse foliage and small leaves, or have branches on which the leaves 

 suddenly turn yellow and die. A whole tree might show similar symptoms 

 and may die, either quickly or after a relatively long period of decline. 

 In many orchards the number of branches or trees showing these symptoms 

 is not great and they are removed, as a matter of course, during the 

 growing season or at the time of pruning. In an increasing number of 

 orchards, however, more and more branches and trees of all ages are dying 

 and their removal is not only time-consuming and costly, but also is re- 

 ducing total yield appreciably. 



Although a number of unfavorable conditions may result in branch 

 or tree death, the most common cause is infection by fungi. The latter 

 penetrate the bark through pruning wounds, bruises or other openings, 

 and cause a collapse of tissues, resulting in girdling and death of the 

 crown beyond the ring of collapsed tissues. 



Several fungi have been found associated with dying apple branches 

 and trees in Massachusetts. Cytospora is the fungus most commonly iso- 

 lated from infected trees of most ages. It is argued, and there are 

 good reasons to believe, that this fungus attacks branches already dead 

 or about to die; but its widespead occurrence in our area on trees of 

 various ages and degree of vigor seems to demand a closer examination 

 of the preferences of this pathogen. Sphaeropsis is the next most com- 

 monly found fungus on apple and it not only kills branches but also 

 causes fruit rot (black rot) and leaf spots (frogeye leaf spot) . Other 

 fungi isolated from apple cankers include Phomopsis (rough bark) , Phoma 

 (Brooks fruit spot) , Cytosporella , Botryosphaeria , Gloeosporium (apple 

 tree anthracnose) , and Fusarium. 



These fungi usually persist on infected apple branches and prunings, 

 sometimes on infected fruits or leaves and, in a few cases, on other 

 kinds of trees near the orchard. All of them produce spores on the in- 

 fected tissues. In most cases the spores are contained within dark or 

 amber-colored fruiting bodies which can be easily seen on the bark of 

 affected tissues at certain times of the year. The fruiting bodies of 

 the various fungi mature at different times during the growing season; 

 thus, some of them release their spores in the spring, others in the 

 summer or early fall, and some produce spores throughout the growing 

 season. The spores are carried from branch to branch and from tree to 

 tree by rain, wind, insects, birds, and by man and his tools. 



Whether or not new infections will take place in an orchard depends 

 on the presence of fungus spores in the area, the condition of the trees, 

 temperature and moisture at the time the spores land on the trees. The 

 presence of large cuts or wounds on branches seems to promote the onset of 

 infections , and many infections begin at very small wounds made by the 



