8 



method should be employed in all cultural operations of prun- 

 ing, choice of soils, fertilisers, stocks and the like, just as it 

 should be in the destruction of pests. All these cultural factors 

 immensely affect the incidence of disease, and every mycologist 

 would admit that sound cultivation does more than anything 

 else to reduce outbreaks. Approved methods of culture for fruit 

 trees will be found in Sectional Volume No. 4 (Fruit Cultiva- 

 tion), to be published shortly. 



One of the chief weapons of this nature at the disposal of 

 the grower is the use of disease-resistant varieties. The breeding 

 and raising of new varieties is a slower process with fruit trees 

 than with many other crops, but with the large number of 

 varieties already in existence much may be done by judicious 

 selection. In substituting resistant varieties for those pre- 

 viously grown, it is first of all necessary to ascertain whether 

 they are suited to the soil and climate of the district. This 

 being assured their employment in the orchard will not only 

 save endless labour but may mean the difference between 

 success and failure. In most of the leaflets notes are given 

 on the relative susceptibility of varieties. It is sometimes 

 found, however, that when good growth and resistance to the 

 disease in question have been obtained, the variety suddenly 

 falls a victim to another pest. Early and prompt attention is 

 then essential and if given will often prevent the new fungus 

 from becoming firmly established. 



In spite of the very best culture and the most suitable 

 varieties certain diseases invariably appear, and it is here that 

 the most accurate knowlege and the most recent results of 

 scientific inquiry will be of most value. No disease has yet 

 been exhaustively investigated, and it is only by further re- 

 search that the many problems can be solved and effective 

 measures of control discovered. 



A. D. COTTON, 



(Mycologist, Ministry of Agriculture and Fisheries). 



London, S.W.I. 



October, 1921. 



