MAINE AGRICULTURAL EXPERIMENT STATION. I9IO. 4OI 



The chief loss caused by these diseases is in injuring the ap- 

 pearance of fruit and thereby lowering its market value. Neither 

 sooty blotch nor fly speck is of so common occurrence in Maine 

 as they are farther south. Where thorough spraying is done, 

 these diseases are effectually controlled. 



SpJiacropsis leaf spot. Leaf spot is a common and widely 

 distributed disease of the apple in oMaine. With some varieties 

 and under certain weather conditions a spotting of the leaves is 

 caused by spray injury, see p. 390. It is a matter of common 

 observation, however, that orchards or trees which have never 

 been sprayed are often affected with a spotting of the leaves 

 which in some cases is quite serious. 



Affected leaves show little spots of dead tissue, usually some- 

 what circular in outline. The dead portion is not quite so thick 

 as the surrounding green tissue and takes on a brown color. 

 On the dead spots little black bodies are frequently found which 

 are the fruiting portions of the fungi associated with the spots. 

 The dead spots often show concentric rings. 



Leaf spot of the apple has been discussed by a large number 

 of writers and the cause attributed to a number of different 

 fungi. In many cases the fact that a certain fungus was very 

 frequently found on the spots was taken as sufficient evidence 

 that it was the cause of the disease. Of recent years it has been 

 questioned whether the presence of a fungus on a leaf spot, no 

 matter how constantly it occurred there, should be taken as evi- 

 dence that the fungus caused the disease. It has been held that 

 i1 is necessary to isolate the fungus in pure culture and then pro- 

 duce the disease by inoculation under control conditions before 

 the matter could be definitely settled. In the summers of 1906 

 and 1907 Scott and Rorer* made a study of the disease in the 

 Ozarks in which they isolated fungi from leaf spots and carried 

 on inoculation experiments. Of the various fungi isolated 

 Sphaeropsis malonnn Pk., the same fungus which causes a de- 

 structive fruit rot (p. 404) and limb canker (p. 414) in Maine 

 was the only one capable of causing the disease when its spores 

 were sprayed on the leaves. 



On account of the importance of the fungous leaf spot in 

 Maine it was thought desirable to make a thorough study of the 



*Scott, W. M., and Rorer, J. B., Bureau PL Ind., U. S. D. A.. Bui. 

 121. Part V, pp. 47-54, 1908. 



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