134 FRUIT CULTURE. 



however, may be left much closer, but should not in any 

 case be crowded in bunches. 



Pests and Diseases. The pear is less liable to insect 

 pests than any other fruit tree. It is, however, occasion- 

 ally visited by red spider and green aphis. The insecti- 

 cides, as before recommended, may also be applied here. 

 The bark scale, canker and other diseases are treated in 

 Part I. 



Cracking in pears is a frequent and troublesome occur- 

 rence, and in many cases the cause is beyond control, as 

 it is induced principally by sudden changes in tempera- 

 ture. Some varieties, however, suffer much more than 

 others. A sudden fall in the temperature causes the 

 skin to stop swelling and become hardened, with the 

 result that when the temperature again rises, and the sap 

 flows freely, the fruit recommences to swell and the skin 

 cracks. Continuous rains often cause cracking, as the 

 ground becomes sodden and cold. Therefore keep the 

 soil porous and open with good drainage, and if the 

 weather is dry, mulch the surface, which will keep it cool 

 and moist and at an even temperature. 



Plums, Fan-Trained. 



The treatment described for pears as to pruning and 

 root-pruning also applies to plums. 



Thinning. In some seasons plums will set immense 

 crops of fruit, in which case it will become necessary to 

 thin considerably. It is a good plan to go over them 

 twice, commencing when they are no larger than a small 

 hazel-nut, and thinning severely if they are thick. Go 

 over them again when the fruit is about half-grown, when 

 it may be used for cooking. The smaller varieties, such as 

 Green Gage, may be thinned to about three or four inches, 



