APPLE AND PEAR SCAB. 



91 



APPLE AND PEAR SCAB. 

 By M. C. Cooke, M.A., LL.D., A.L.S., F.R.H.S., V.M.H. 



This disease is the most universal and destructive of any which hitherto 

 has attacked the Apple and Pear. It may be treated as one disease on 

 both fruits, although the fungus which produces it is slightly different in 

 the two cases, it being known scientifically as Fusicladium dendriticum 

 when occurring on Apple, and Fusicladium pirinum when attacking the 

 Pear. There are slight differences in the sporules or conidia of the two 

 species, which account for the difference in the name. The habit, 

 external appearance, life-history, development, and remedies are the same 

 in both cases. 



The black mould which causes the disease appears sometimes on the 

 young twigs before the leaves have expanded, on the young or mature 

 leaves, and on the fruits, even in their earliest stages and in their more 

 mature condition. It is sometimes called the Apple or Pear Scab, and 

 sometimes Black Spot. Not only is it known throughout Europe, but it 

 is one of the greatest pests in North America and in Australasia, being" 

 found wherever these fruits are cultivated. 



The Illinois Horticultural Society has estimated the loss of fruit from 

 this disease in each county of the State in Apples alone to be 20,000 

 bushels, or a value of 400,000 dollars for the entire State. In Missouri 

 the loss is estimated at half the crop, in Kansas one-fourth of the crop, 

 and in Indiana about one-sixth of the crop. In America it is most severe 

 in seasons when damp cold weather prevails at the time the fruit is 

 forming. In dry warm springs there is a marked absence of the disease. 

 It is more prevalent in heavy soils, where drainage is poor, than in light 

 well-drained lands. 



In Australia the Department of Agriculture, Victoria, estimated in 

 1902 that over eight thousand acres the sum of £40,000 may be taken 

 as roughly representative of the annual losses in Victoria on Apples 

 alone. The Agriculture Gazette of Tasmania states that " this disease 

 does more damage and occasions more loss than all the other pests 

 combined." 



On the leaves there first appear small dark olive patches with a 

 rounded outline. As these increase in size their surface appears velvety, 

 and the margins become more irregular, and sometimes two or more spots 

 are confluent. Although most frequently on the upper surface of the 

 leaves, spots sometimes appear on the under side and upon the petioles, 

 occasionally on the young twigs. 



On the fruit the development of the spots is similar. They appear to 

 start from a centre of infection preserving a rounded form. The sp 

 increase in size, the cuticle cracks, and forms a light-coloured ring about 

 their margin, the greatest vigour remaining about the margin where the 

 fruit seems stimulated to the production of a sort of corky layer m its 

 effort to throw off the disease, which results in the formation of a kind of 



