248 EXPERIMENTAL \FARMS 



2 GEORGE V., A. 1912 



apple rust and cedar ' apples/ (Gymnosporangium Macropus, Link). 



Many observers are familiar with the woody galls so frequently found on the 

 Red Cedar (Juniperus virginiana) but probably few are aware that these 'cedar 

 apples,' as they are called, are connected with the ' rust ' of apple trees. Yet such 

 is the case, and although ' apple-rust ' is, in this country, rarely reported as a serious 

 disease, it may be of interest to briefly outline the life-cycle of the fungus which gives 

 rise to two such widely different effects. 



In the spring time, after rains there will be noticed protruding from the cedar- 

 apples a number of orange-coloured, gelatinous, and usually horn-like outgrowths, pro- 

 duced by the swelling of the masses of resting spores inside the gall. On the surface 

 of these protuberances, vast numbers of minute spores are formed and, as the gelatin- 

 ous mass dries, these spores are scattered by the wind. If blown on to certain parts 

 of an apple or crab tree, such as the leaf or young fruit, or occasionally the young 

 twigs, they produce infection of this new host, and the green colour of the healthy 

 tissue becomes changed over the infected area to a yellow or orange tint. Later on, 

 there will be found arising from this spot small, tubular outgrowths of a yellowish or 

 cinnamon colour, inside which are produced spores of another kind. This is the 

 apple ' rust ' and corresponds to the ' cluster-cup ' stage of the common grain rust 

 found on the Barberry leaf with the rim of the cup prolonged into a tube. The spores 

 now borne can only produce a further development if carried to the Red Cedar where 

 they give rise again to the cedar-apples, a process which occupies two seasons. 



Control. 



The only satisfactory means of preventing the disease on one of the alternate 

 hosts is to avoid growing the other in the immediate neighbourhood. . Since the apple 

 tree is the important one, except in very exceptional cases, neighbouring red cedars 

 should be cut down and destroyed. A certain amount of infection may still take place 

 by spores carried from a distance but this will be found of negligible amount. In 

 cases where it is desired to keep the red cedars for ornamental purposes, something 

 may be done by cutting off and burning all cedar apples before the horn-like out- 

 growths have appeared in spring. Spraying has not yielded good results. 



SOOTY MOULD (Capnodium, Sp.) ON APPLE TWIGS. 



During the year, an interesting communication was received asking if a ' Black 

 Knot ' disease, similar to that on plum and cherry trees, is found on the apple. The 

 inquiry was accompanied by a number of twigs encrusted with a black, irregular warty 

 growth, somewhat resembling the excrescence of the familiar ' black knot.' Examina- 

 tion, however, showed this growth to be quite superficial in its nature; the fungus — 

 a species of Capnodium — having developed and produced its fruit bodies around the 

 twigs, but not having entered the tissues of the host. Such fungus growths are not 

 uncommon on various plants and are usually observed in association with aphis 

 attacks, the ' honey-dew ' excreted by these insects on the leaves and branches forming 

 a medium very favourable to the development of the fungus. Such growths are of 

 no particular importance, as a rule, apart from their somewhat unsightly appearance, 

 but at times may cover the surface of the leaves to such an extent as to interfere with 

 their functions. Where insect pests are systematically combated, the conditions neces- 

 sary for such a result are not likely to be found. 



