140 Commercial Gardening 



delicate white bloom, resembling the bloom on a grape. This bloom con- 

 sists of myriads of spores of the fungus growing in the tissues of the leaves, 

 These spores are conveyed by wind and other agents to neighbouring young 

 leaves and shoots, and by such means the disease is spread. In some in- 

 stances the leaves only are attacked, and usually form a sort of rosette 

 at the end of the shoot. In many instances, however, the shoot is also 

 attacked, which is indicated by a more or less pronounced swelling or 

 thickening near the tip. Now when a shoot is attacked the mycelium or 

 spawn becomes perennial in the tissues; that is, it lives in the tissues from 

 year to year, and each season passes into the new leaves, which become 

 infected. The injury caused by this disease is a loss of foliage which im- 

 poverishes the tree, and tells very materially on the quantity and quality 

 of fruit, also on the general growth of the tree, as when shoots become 

 infected they never form any more wood. 



So far as preventive methods are concerned, my advice is to prune all 

 shoots showing leaf curl about 6 in. behind the point where the leaves are 

 produced. The mycelium of the fungus present in the shoots never extends 

 backwards towards older wood, but invariably advances along with the new 

 shoots, where the richest store of food is present to supply food for the 

 growth of the new shoot, into which the mycelium of the fungus passes. 

 Where the disease has existed the trees should be sprayed the following 

 spring with self-boiled lime-sulphur mixture, first just when the leaf buds 

 are expanding (see p. 50). 



Peach Mildew (Podosphcera oxyacanthce). This destructive mildew 

 attacks Apple, Peach, Quince, Cherry, and various other fruit trees belong- 

 ing to the Rose family, but the Peach suffers most, as the fruit is so fre- 

 quently attacked. When the fruit is about half-grown, one or more 

 whitish patches appear on its pale-green surface. These patches gradually 

 increase in size and present a powdery appearance, as if sprinkled with 

 flour. These patches represent the summer fruit of the mildew, arid this 

 is the stage in which the disease is first noticed by the grower, judging 

 from the numerous examples received for identification during an experi- 

 ence of twenty-five years. Nevertheless, in ninety-nine cases out of a 

 hundred, the mildew first appears on the young leaves and shoots, and 

 from thence passes on to the fruit. If a careful watch is kept soon after 

 the leaves are developed, and the mildew arrested on its first appearance 

 on the foliage, by spraying with sulphide of potassium, the fruit would 

 be saved from attack. On the other hand, if the fruit once becomes 

 infected, spraying is practically useless, as the dense mat of down on the 

 surface of the fruit protects the fungus from the fungicide (see p. 51). 



" Die-back" Of Peach Shoots (Ncemaspora crocea). Practically every- 

 one concerned in the cultivation of plants has grasped the fact that fungi 

 can cause diseases. This mostly accounts for the statement repeatedly made, 

 that diseases are much more prevalent now than in times past. There is 

 no evidence to show that such statements are correct. They certainly 

 prove that more attention is being paid to the subject than heretofore. 



