PEAR DISEASES 



1645 



of the crowns and roots below the ground 

 showed the presence of hold-over blisht in 

 certain trees. 



In the case of the Newtowns, which are 

 quite resistant under average conditions, 

 I have found the most serious holdovers 

 in the roots (stock). Here, then, is an 

 important factor in the control of blight. 

 Not only should the part above the ground 

 be examined, but the crown and roots of 

 a tree should be bared so as to be sure 

 that no hold-over exists there. There is no 

 mystery about crown and root infection; 

 certain insect agencies work as readily 

 under ground as they do above. Further- 

 more, in cases of severe blossom, twig or 

 limb infection, infection may be carried 

 down to the roots from above by rain. I 

 have been able to demonstrate the pres- 

 ence of blight germs in droplets of rain- 

 water trickling down the trunks of trees. 

 For many years I have advised the 

 use of sticky bands in the control of in- 

 sects which are known as blight carriers. 

 In this connection it may be said that 

 water-sprouts are not necessarily the only 

 entrance points for root infection. Of 

 course many root infections may be 

 traced directly to infected water-sprouts 

 coming from the crown and roots, but 

 many infections are brought about by 

 direct crown and root infection. The en- 

 trance directly Into the crown and root 

 is usually effected through growth cracks 

 and by means of punctures made by eat- 

 ing, boring and sucking insects carry- 

 ing the germs. Such insects may be 

 caught by the use of sticky bands. 

 Aphides should also be kept under good 

 control, as they are notable carriers of 

 Infection to the succulent growths. 



Tree medication has always been a fav- 

 orite hobby with many people. Theoretic- 

 ally, there may be some basis for work 

 of this kind, but the practice of con- 

 trolling blight by the use of the hypo- 

 dermic needle has proven unsatisfactory. 

 In my investigation work covering a long 

 period of years, I have used all sorts of 

 chemicals and chemical combinations 

 both externally and hypodermically, but 

 so far no promising results have been 

 forthcoming. It is said that a drowning 



man will grasp at a straw; we have 

 grasped at everything, whether it showed 

 promise or not. 



The work of pear blight control must 

 depend, at least for the present, upon the 

 methods which have been worked out, 

 namely, careful eradication of hold-over 

 blight, thorough disinfection, and last, 

 but not least, the control of insect 

 agencies. Of course, certain insects, 

 such as bees, are necessary for pollina- 

 tion, but the time over which they work 

 is very short as compared with the grow- 

 ing season following the blossoming 

 period, and during which period the most 

 serious infections are produced. During 

 the growing season, blight should be re- 

 moved whenever it appears; any living 

 infection should always be considered a 

 center for further spread of infection. 



In future planting we should demand 

 at least resistant roots for our commer- 

 cial varieties of apples and pears. Al- 

 ready many nurserymen are growing 

 commercial varieties worked on resist- 

 ant roots, and many have even gone so 

 far as to grow resistant varieties for top- 

 working. The control of blight is not so 

 difficult when the framework, body and 

 roots are all resistant to blight to the ex- 

 tent that hold-overs will rarely occur in 

 them. 



The development of commercial varie- 

 ties equal to our well-known varieties 

 and at the same time resistant to blight 

 is an ideal we have been striving to- 

 ward for many years. Many European- 

 Oriental hybrids of considerable resist- 

 ance have been produced, but their qual- 

 ity does not compare with our well- 

 known commercial varieties. Breeding 

 and selection will In time solve the ques- 

 tion of blight control, but for the present 

 we must adopt the best practice known 

 to save the pear and apple orchards now 

 growing. Experimentation should go on, 

 but in a dangerously infectious disease, 

 such as pear blight is, all experimenta- 

 tion should be taken out of the hands of 

 the amateur. Much of our trouble In the 

 control of this infectious disease is due 

 to a desire to experiment on the part of 

 those wholly unfit for work of this kind. 



