144 



PRINCIPLES OF FARM PRACTICE 



the fruit so that it will be borne on the stronger branches 

 near the trunk, thus reducing the possibility of branches 

 being broken by the weight of the fruit. 



Insects and diseases. Each kind of tree has its own 

 difficulties with insects and diseases. For example, the fruit 

 of the apple tree is injured by a disease known as apple rot 

 and by an insect called the codling moth. Apple production 

 is interfered with by many other diseases and insects, but 

 these are mentioned as important examples. Control of 

 insects and diseases is absolutely necessary for successful 

 fruit -raising. In general, spores which may develop into 

 fungi and cause disease are destroyed by means of chemical 

 mixtures known as fungicides, and insects are killed by means 



of poisons. Both are applied in 

 the form of a solution by means 

 of sprays. Usually the application 

 of a fungicide for control of plant 

 diseases is made in the spring 

 before the buds open, but in some 

 cases it may be made when the 

 tree is in full leaf. In either case 

 the spray is intended to kill the 

 Diagrams showing successive spores of the disease-producing 



stages in making a graft. (Cal- fungus. For example, if peach 

 ifornia Agr. Exp. Station.) trees are sprayed before the buds 



swell, with the Bordeaux mixture, the spores of the fungus 

 which causes leaf curl will be destroyed, and this injury 

 controlled. The control of insects by the application of 

 poisons depends upon the habits of the insects. For example, 

 it is the habit of the plum curculio to make a hole in the 

 plum and deposit eggs. She may be injured before egg laying 

 is accomplished if a poison, such as arsenate of lead, is 



