LEAF SPOT-. 11 



the fruit buds in late summer, especially on Limbertwig, Missouri, 

 and Ben Davis trees, and suggested thai possibly the apple-blotch 



fungus was also responsible for this trouble. An investigation 

 showed that both the apple-blotch fungus and the black-rot fungus 

 {Sphaeropsis malorum Peck) were present in the diseased bud-. 



Observations in the orchard and culture work in the laboratory 

 showed that the apple-blotch fungus extended down from diseased 

 leaf petioles into the twigs at the base of the buds, which were soon 

 killed. It was found that Sphaeropsis soon invaded the diseased buds 

 and perhaps assisted in killing them. This trouble begins to show 

 about midsummer and becomes more pronounced as the season 

 advances, sometimes injuring the fruit buds of a few varieties to 

 such an extent that the crop the following year i< almost a failure. 

 During 1907 a similar diseased condition of Winesap buds was 

 found to be common in Arkansas and Mis>ouri. As this variety 

 i- practically immune from the Phyllosticta disease, some doubt was 

 thrown on the conclusion given above. Cultures from these diseased 

 Winesap buds nearly always developed Sphaeropsis malorum, but 

 failed to show the presence of Phyllosticta. It would seem, therefore, 

 that at least in the case of the Winesap the black-rot fungus i> 

 capable of killing the buds without the aid of the apple-blotch 

 fungus. However, a further investigation of the cause of this 

 trouble is desirable. 



LEAF SPOTS. 



The spots on the leaves caused by the apple-blotch fungus are irreg- 

 ular, light brown, yellowish, or whitish, and quite small, measuring 

 one-sixteenth inch or less in diameter. Each spot bears one to several 

 small black pycnidia. These diseased areas are scattered promiscu- 

 ously over the surface of the leaf, and frequently occur on the veins, 

 midrib, and petiole. (PI. I. fig. 5.) They are so minute that several 

 dozen may occur on a leaf without attracting attention and perhaps 

 without material injury, but in severe ca>es they become conspicuous 

 by their number-, several hundred frequently occurring on a 

 single leaf. The badly affected leaves may drop prematurely 

 or die and turn brown on the tree. The latter condition results from 

 a girdling of the petiole by the fungus, and often in midsummer 

 such susceptible varieties a- the Missouri and Limbertwig show tufts 

 of brown leave- involving half or more of the foliage. This results 

 in a weakening, and in many cases the death, of the fruit buds for 

 the following year'- crop. However, a- a Leaf-spot disease it i- of 

 comparatively minor importance, the common leaf-spot being caused 

 by Sphaeropsis malorum Peck, which produces much larger spots. 



144 



