THE MONTHLY BULLETIN. 511 



Resume. 



It becomes evident that the amount of injury insects are capable of 

 inflicting in the spread of pear blight, depends directly upon the amount 

 of blighted material that is available to them in their search for food. 

 This is true from the very first transmission of winter blight into the 

 spring growth to the end of the infection period, and throughout the 

 range of insect life from those which search out and feed upon blight 

 to those Avhich come upon it unwittingly and thus become factors in its 

 distribution. Through the agency of the former class, however, the 

 amount of infection increases so rapidly that this does not always seem 

 to be true. An orchard from Avhich a few evident cases are removed 

 on a certain day may in the course of another week contain many times 

 more than were at first removed from it. This is due to the fact that it 

 requires from four to six days after inoculation, even when the sap is 

 most active, for the disease to become evident. Several days before they 

 are evident, however, these cases are in a condition to distribute infec- 

 tion; indeed, by the time they have blackened sufficiently to be easily 

 found tlicy have passed their prime as factors in the spread of the 

 disease. This is especially true of flowers, which may contain nuich 

 blight exudate while still appearing fresh and healthy. Twigs are often 

 found to bear lieads of lateral exudate before th(>y have wilted sufficiently 

 to attract attention. These cases especially attract insects which inten- 

 tionally make blight exudate a part of their diet. Adding to this the 

 number of these insects that have received the germs from blight already 

 removed, it will be seen that there is a perpetual source of infection 

 and that the progression is an enormous one. It is not as great, however, 

 when these cases are removed as fast as they appear as when they are 

 left to continue down the limbs, gnnuning as they extend and thus event- 

 ually necessitating the removal of more and larger Avood. meanwhile 

 serving as perpetual sources of infection to swell the percentage. 



Within the second class of insects it is especially true that profuse 

 infection greatly increases their capacity for inflicting injury. A tree 

 in which 50 per cent of the growth is blighted contains one chance out 

 of every two for further contamination from it by every insect that feeds 

 upon it; so while summer cutting may be discouraging on account 

 of the pei'petual reappearance of blight, and while it is never successful 

 as eradication, it is certainly a most important aid, when properly done, 

 in minimizing the ravages of this disease. Its danger lies in improper 

 or incomplete methods, namely: short cutting, lack of disinfection and 

 negligence in biuming infected parts when removed. The growers who 

 cut too short or fail to disinfect are doing exactly Avhat the insects are 

 doing, and are capable of far more damage than they. 



