3DO MAINE AGRICULTURAL EXPERIMENT STATION. IQIO. 



This fungous leaf spot causes a considerable amount of loss 

 in Maine orchards and this loss is not always realized by the ap- 

 ple growers. The dead spots in the leaves interfere with their 

 function, and, in addition to this, large numbers of the diseased 

 leaves fall prematurely, thus seriously interfering with the nutri- 

 tion of the trees. 



As has already been mentioned the fungus causes the canker 

 of the wood and the black rot of the fruit, therefore preventative 

 measures must be directed toward all 3 forms of the disease. 

 Since inoculation experiments indicate that in Maine infection 

 must take place before the middle of July spraying as recom- 

 mended for apple scab would do much to control the disease. 

 This should be supplemented with the removal and destruction 

 of limb cankers and decayed fruit. 



From their observations the writers are convinced that leaves 

 of trees which are well fertilized, cultivated and generally well 

 cared for are not so susceptible to the disease as the leaves of 

 neglected trees. It must be borne in mind, however, that a sim- 

 ilar spotting of the leaves of susceptible varieties may occur as 

 the result of spray injury. 



Rust. This disease of apple leaves and fruit which does great 

 damage in some apple growing districts does not seem, accord- 

 ing to the observations of the writers, to be of very common 

 occurrence in Maine. The fungi* which cause this trouble pass 

 a part of their life upon the apple and related plants and a part 

 upon the red cedar where they cause the abnormal development 

 of small brown knots on the twigs which are known as "cedar 

 apples." In the spring these knots produce thread-like tubes 

 which when wet with rain swell up, become gelatinous, are 

 orange-yellow in color, and throw off large quantities of spores. 

 These spores are capable of infecting apple leaves and are pro- 

 duced when the latter are young and most susceptible to infec- 

 tion. 



On the apple leaf there is first a thickening of the tissues in 

 small spots at the points of infection. Later in the season these 

 thickened places become ruptured on the under side and short, 



* Apple rust may be produced by Cymnosporangmm inacrocarpus Lk., 

 or G. globosum Farl. It is not known which species is responsible for 

 the rust in Maine but probably it is the latter. The red cedar, Juni- 

 perus virginiana L. is the alternate host for both. 



