246 EXPERIMENTAL FARMS 



2 GEORGE V., A. 1912 



fungus causing this disease. These ruptures are rarely absent and at the proper time 

 they contain ripe spores of the fungus which, at later periods, may no longer be found 

 therein. So any careful observer can, by means of a pocket lens, easily determine 

 whether an injury is due to frost or to the fungus. This confusion, no doubt, accounts 

 for some of the unsuccessful attempts in combating the disease by sprays. 



Apple-tree Anthracnose manifests itself on branches of apple trees by clearly 

 defined, depressed, dark-brown areas of more or less large dimensions. If the disease 

 is allowed to make unchecked progress, it will completely girdle the attacked branch, 

 which will consequently die. There may be a large number of separate infections on a 

 single tree. During the winter months, the progress of the fungus is almost at a 

 standstill, but early in the spring it becomes active again, which may be noticed by the 

 increase in circumference of the dead areas. In May or June small ruptures appear 

 in the bark where the fungus produces a large number of single-celled colourless 

 spores of the genus Glceosporium. . These spores germinate and reproduce the disease 

 when they encounter favourable conditions for their development. 



From the life-history of the fungus, we would suggest the following means of con- 

 trol : Remove all branches that are girdled or very nearly girdled by the disease 

 and burn them. All trees should be sprayed with lime sulphur in autumn, not later 

 than when all leaves are off the trees. Early in spring, this spray should be repeated 

 to be followed shortly before the unfolding of leaves or flowers by Bordeaux mixture. 



black rot (Sphceropsis Malorum, Peck). 



Although this disease has been found on pears and quinces, our records of its 

 occurrence in this country are confined to the apple. It may appear on the leaves, 

 fruit, or woody parts of the tree, producing more or less characteristic effects. 



On the fruit. — This is perhaps the best -known form and its appearance has led to 

 the name ' Black Rot ' being applied to it, a name now used for the disease in general. 

 The apples are infected through some injury (wasps, curculio, hail, etc., etc.) The 

 diseased flesh becomes discoloured, but remains firm and, later, its entire surface 

 becomes covered with minute black pustules. Each of these black bodies is a fruiting 

 body or pycnidium, inside which spores are produced. This phase of the disease is 

 comparatively unimportant, rarely causing an appreciable loss. 



On the leaves. — Here a characteristic spotting is produced. The spots vary 

 from I to £ inch in diameter, and are of a brownish hue surrounded by a well-marked 

 purplish border. The pycnidia do not, as a rule, develop till the leaves have fallen to 

 the ground. 



On the limbs and trunk. — It is here that the most serious effects are produced, 

 the growth of the fungus giving rise to ' cankers ' of the large limbs of old trees and of 

 the trunk as well in the case of young trees. These differ from the cankers due to 

 ' fire blight ' in being raised rather than sunken, and in having the surface cracked 

 and roughened instead of smooth. Later, the surface becomes covered with the little, 

 black fruiting bodies previously referred to as occurring on the fruit. These cankers 

 are perennial and often have a zoned appearance as a result of the growth in succes- 

 sive seasons. They may extend for considerable distances up and down the limb and 

 finally work right round it, girdling it and causing its death. The damage done by 

 this ' black rot canker ' has recently created considerable alarm in certain districts 

 in Ontario, particularly in Prince Edward county. 



Control. 



Prevention of the disease largely resolves itself into general care of the apple 

 orchard and the selection of varieties hardy enough to be proof against winter injury 

 ir the locality under consideration. 



