324 



The Canadian Horticulturist. 



-^ (D^^c^tioi) ^Pd^bC^P. ^ 



SHOT HOLE FUNGUS. 



494. Sir, — My plum tiees made a rapid growth during the first part of tlie season 

 and were heavily laden with fruit, but, about the latter end, 6th .July, the leaves appeared 

 as if scorched and have since dropped, leaving the trees almost bare The fruit, however, 

 still remains on the trees, but has grown very slowly. Can you tell me the cause and cure? 



R. Tkotter, Oiven Sound, Ont. 



The leaves enclosed by our correspondent are riddled with small, round 

 holes, as if made with small shot, for which reason this disease has been called 

 the shot hole fungus. It is known to scientists as Septoria Cerasina. It attacks 

 the foliage of both the plum and the cherry, and, though not usually so 

 serious as in the case before us, inflicts considerable injury by interfering with 

 the proper function of the leaves, or by causing them to drop prematurely. The 

 leaves attacked first show dark purple spots, visible on both sides, from one 



Fig. 83 — Shot Hole Fungus. 



twenty-fourth to one-eighth of an inch in diameter. The tissue covering these 

 spots soon becomes dead brown in color and finally drops off from the leaf 

 entirely, leaving numerous clear-cut, round holes, such as are well shown in 

 Fig. 83. 



Under the microscope we may detect, upon the under surface, very minute 

 black spots. These spots are the fruit of the fungus-like capsules in which the 

 spores of the fungus are produced in great abundance. These are very slender, 

 many times longer than broad, and (juite transparent. Each spore is divided by 

 cross walls into two or more cells, each of which is capable of producing a new 

 parasite. The spores live through the winter on the old leaves, and thus serve 

 to propagate the fungus in early spring. 



In Vol. XIII, J). 316, may be seen an illustration of an highly magnified 

 section through the leaf, including one of the spore capsules above described, 

 and at a above are shown some spores still more highly magnified. 



Nothing can be done at this season beyond destroying in some way, if 

 possible, the old leaves. The best treatment, however, will be a preventive one. 



