Introduction. 3 



the field was first and is still too often stimulated and helped by 

 them. Full use has been made of the many valuable notes not only 

 of how we may check these enemies, but of their various ways, sent 

 by many correspondents. The writer knows of several growers who 

 could better have written this thesis, and probably many others have 

 gone before who could have done the same. 



The subject of spraying has not been dealt with at any length in 

 this volume, but where it is of some, or even possible benefit it has 

 been referred to and a general summary of the various washes in use 

 is given in an appendix.* The author cannot help suggesting this 

 advice look upon the washing of fruit trees as only a small adjunct 

 in fruit-growing. First, because we know as yet very little of any 

 definite use ; secondly, because great sums of money are too frequently 

 wasted on washing healthy trees ; thirdly, because so many of the 

 washes used are harmful to the trees. What is the object of dosing 

 a man with this or that drug as a remedy if he is well, unless it 

 is to prove a " certain cure " to advertise some quack preparation. 

 If one looks over any number of unhealthy fruit trees one can see at 

 once very many unhealthy signs, many forms of actual disease, many 

 sequelte of diseases. How many of these are due to insect and fungoid 

 enemies ? There are probably just as many pathological diseases, 

 stages and degrees of unhealthiness in plants as in man, and yet all 

 we think of, all we try to cure with wonderful washes are the purely 

 parasitical diseases. 



Parasitology is most interesting, of enormous importance in 

 human and animal as well as in plant disease, but we must not lose 

 sight of the fact that it is only one factor in disease when we deal 

 with fruit trees, as the doctor does with man and as the veterinary 

 surgeon with animals. 



With man and animals two things we notice in connection with 

 parasites : first, dirty, unsanitary and unhealthy conditions encourage 

 the unbidden guests ; secondly, a weakened or diseased condition of 

 the host predisposes it to these baneful enemies. So it is with our 

 fruit trees ; every grower knows that certain trees or varieties will 

 not grow on certain lands, they become unhealthy and then they 

 become cankered ; he knows under certain other conditions they 

 fail and become diseased. 



An old, neglected, dirty orchard may often swarm with insect, 

 mite, bacterial and fungoid pests. So do clean orchards when the 



* For fuller information on various insecticides the reader is referred to 

 ' Fruit Trees and their Enemies, with a Spraying Calendar,' by Spencer U. 

 Pickering, M.A., F.R.S., and Fred. V. Theobald, M.A. (1908). Price Is. 6d. 



B 2 



