126 EXPERIMENTAL FARMS 



9-10 EDWARD VII., A. 1910 



all aphis at one application ; indeed, it is almost impossible to spray them all with the 

 mixture when the leaves are curled. 



DISEASES OF THE NATIVE PLUM (PRUNUS NIGRA). 



Diseases of fruit were not as troublesome in 1908 as in some years, doubtless 

 owing to the warm, dry season. There are, however, two diseases to which attention 

 should be drawn, as they have proved so injurious to the native plum (Prunus nigra), 

 and have in many places in eastern Ontario and Quebec ruined the crops of that 

 fruit, which, where the European varieties of plums cannot be grown, is of consider- 

 able importance to settlers over a wide area of country. 



Spot or Blight of the Native Plum (Cladosporium carpophilum V. Thumen). — 

 The almost complete absence of native plums during recent years in the Ottawa 

 district and elsewhere in Eastern Ontario and the province of Quebec, is due in a large 

 measure or almost entirely to the disease known as blight. The fruit forms and 

 reaches more than half its size, but colours prematurely. When affected by the disease 

 it shrivels and falls to the ground without ripening. If the fruit is examined when 

 half grown or later, small pale green or yellow patches will be noticed. These gradu- 

 ally enlarge until finally they are about half an inch in diameter, at which time the 

 blotches are darker in colour, of more irregular outline and are raised on the skin. 

 The Americana plums are not, as a rule, seriously affected with this disease, which is 

 principally confined to the Nigra varieties. 



Eemedy. — This fungus is nearly related to the apple spot, and can be satisfac- 

 torily treated in much the same way. The trees should be sprayed with Bordeaux 

 mixture just after the blossoms fall, again two weeks later, and a third time two 

 weeks after the second application. It is also advisable to spray a fourth time with am- 

 moniacal copper carbonate just when the fruit is beginning to colour. The native 

 varieties ripen early, and if the ordinary Bordeaux mixture were applied the last time, 

 the fruit might remain stained. The ammoniacal copper carbonate does not leave a 

 noticeable stain on the fruit. This remedy has been very satisfactorily used by one 

 grower in particular near Ottawa, who has thus been able to grow native plums very 

 profitably, and at the Experimental Farm spraying with Bordeaux mixture has kept 

 the disease under perfect control. The Americana varieties may be top grafted on the 

 native ones, with the result that there will be less disease as the former are not as much 

 afl'ected as the native. All other plum trees not looked after or bearing poor fruit 

 should be burned; also all fruit which is. diseased. 



Plum Pockets (Exoascus pruni Fckl.). — The disease known as plum pockets has 

 been recently very injurious to the native plum (Prunus nigra), the entire crop of 

 fruit in many cases being ruined by this disease. The mycelium of the disease which 

 causes the pockets is able to live for more than a year in the tree, and although the 

 pockets may not be produced one year the disease may be in the tree, and if conditions 

 are favourable the next year the tree may be covered with them. It is thus not neces- 

 sary for the disease to start from spores every year. The fruit is affected soon after 

 tlie tree has blossomed, and is indicated by the unnatural swelling and bladder-like 

 appearance of the fruit and by its unusual yellow colour. There is no stone in fruit 

 affected by this disease. When the spores of the disease which has been working in- 

 side the fruit appear on the surface they give the pockets a grey appearance. Later 

 on the pockets turn almost black and fall to the ground. The leaves and twigs are 

 also noticeably affected with this disease, the former becoming curled and unhealthy 

 looking and the twigs swelling unnaturally. There is no known thoroughly tested 

 remedy for this disease, but as it is closel.y related to the peach leaf-curl, which is 

 controlled by early spraying with Bordeaux mixture (4 lbs. bluestone, 4 lbs. lime and 



