118 



The fungus infects not onlj^ the fruit 

 but also the leaves and the young shoots. 

 On the dark brown spots which appear 

 on the leaves numerous spores are pro- 

 duced which, falling on the fruit, cause 

 infection of the crop. When the young 

 shoots are attacked the fungus lives 

 within the tissues through the autumn 

 and winter, and in the following spring 

 bursts through the bark as small cushion- 

 like pustules. This rupturing of the bark 

 causes the twigs to have a roughened 

 cankered appearance, which is a charac- 

 teristic feature of this disease. Spores 

 are formed on the surface of the pustules 

 and these under favourable conditions 

 reproduce the disease on the new season's 

 leaves and fruit. It is evident therefore 

 that the fungus is able to persist from 

 year to year on the infected twigs, and 

 when practicable these should be pruned 

 off and burnt. 



A closely related fungus, Venturia 

 Pyrina is the cause of a similar disease 

 of pear trees, the fruit, leaves and shoots 

 becoming affected; the fruit is, as a result 

 of this disease, very frequently malformed 

 and cracked. 



As a preventive against infection by 

 the scab fungi, a protective spray should 

 be applied to the trees. Bordeaux Mix- 

 ture and Lime-sulphur are both effective 

 washes for use in the control of this 

 disease. Bordeaux Mixture of the for- 

 mula 8:8: 100 is safe for use on pear trees 

 and some varieties of apples, but on 

 others a scorching of the leaves and fruit 

 occurs, and Lime-sulphur is preferable. 

 In the case of certain varieties which are 

 very susceptible to spray injury, e.g.. 

 Cox's Orange Pippin, Lime-sulphur at 

 half the usual summer strength, i.e., S.G. 

 1.005 (one gallon of the concentrate at 

 S.G. 1.3 to 59 gallons of water) must be 

 used to avoid scorching. 



The first spraying should be carried out 

 on the young foliage just before the 

 flowers open, and a second as soon as the 

 fruit has formed; where the disease has 

 been severe in previous years a third 

 spraying may be necessary. 



Apple Mildew. 

 When the young apple shoots are 

 elongating in spring it is frequently found 

 that the leaves on some of the shoots are 



checked in growth, and coated with a 

 white powder which consists of the spores 

 of the Apple Mildew (Podosphaera 

 leucotricha). The flowering shoots may 

 also be attacked, the flowers in conse- 

 quence becoming deformed, and fail to set 

 into fruit. The disease may also extend 

 to the very young fruit, and occasionally 

 it occurs on older apples. On some 

 varieties the leaves may be so severely 

 affected that many are killed and fall off, 

 leaving a number of bare twigs. 



Fig. 2.— Apple Mildew. 



In addition to the powdery summer 

 stage this fungus (in common with 

 other powdery mildews) produces fructi- 

 fications which persist through the winter 

 and disperse their spores in spring; these 

 winter fructifications in the apple mildew 

 are, however, of infrequent occurrence, 

 and its usual mode of surviving the winter 

 is by the development of hibernating 

 mycelium (non-fruiting fungal threads) in 

 the buds of the young twigs. The leaves 

 which grow from such infected buds again 

 give rise to the powdery summer stage, 

 and the spores, on being blown about, 

 start new infections. 



All infected shoots should be pruned 

 off and burnt ; these may be distinguished 

 in spring and summer by their white, 

 mealy leaves (Fig. 2), and in winter by 

 the grey or whitish appearance of the 



