No. 6. DEPARTMENT OF AGRICULTURE. . 593 



PEAR BLIGHT. 



This disease, which is caused by a bacterial germ, occurs on the 

 pear, apple, quince, and other plants of the Pome family. It has 

 been one of the stumbling- blocks in orchard diseases for years, but 

 during the last few years through the careful working out of the 

 life history of the bacillus which produces it, we are now able to 

 control this trouble. It is only a question of careful thorough work. 

 This disease is transmitted by insects on the blossoms, not only the 

 common honey bee, but flies, wasps and other insects carry it from 

 flower to flower and from orchard to orchard. It is also occasionally 

 carried long distances by birds. This disease is infected mainly 

 through the blossoms, but it is also infected to a large extent 

 through the tender tips of growing twigs and occasionally through 

 the fleshy bark of twigs and branches. Most of the germs die out 

 in the tree shortly after they are produced, but occasionally the dis- 

 ease is able to continue in the tree until autumn. Along the ad- 

 vancing margin of the trees the germs keep alive and if they can 

 keep on multiplying until the tree goes into a dormant condition in 

 the winter, they are able to live through the winter and begin to 

 grow again the next spring. When root pressure gorges the tree 

 with sap in the spring this causes the blight to start off with re- 

 newed vigor. A gummy substance exudes unto the bark under cer- 

 tain weather conditions and this gummy exudate is the virus of the 

 disease, is carrier onto the opening blossoms and thus the disease 

 spreads. These hold over cases become the new infection centres 

 each spring. The blight has no other means of living over winter. 

 Such cases therefore constitute the key to the whole pear blight 

 situation. Cutting them out and destroying them puts an end to 

 the disease so far as any orchard is concerned. The cutting out has 

 to be skillfully and thoroughly done. A disinfectant has to be car- 

 ried when doing this cutting and the knives and saws kept thor- 

 oughly wiped sterile to avoid spreading the disease. It is also nec- 

 essary to wipe off the wounds after each cut. For this purpose cor- 

 rosive sublimate solution with the strength of 1 to 1,000 in water is 

 the best material. 



PEACH YELLOWS. 



This disease has attracted a great deal of attention in past years. 

 In fact, it has been considered one of the most obscure and difficult 

 diseases in the whole category. It still remains in this class as far 

 as its cause is concerned. 



Pathologists have been wholly unable to find out the cause of the 

 disease. On the other hand when it comes to the remedy this dis- 

 ease is the easiest to control and is the most economically combatted 

 of any of our serious orchard troubles. The method of control con- 

 sists of a thorough inspection of each tree in the orchard during its 

 fruiting period and the prompt removal of the tree by digging it up. 

 The safest plan is to burn the tree on the spot. As' a rule the dis- 

 eased trees can best be found by inspecting them at the time of the 

 ripening of the fruit, but as a general method of procedure it is well 

 to inspect them tree by tree and row by row, three or four times dur- 

 ing the season, once in July, once in August and once in September. 

 38—6—1905 



