272 STATE BOARD OF AGRICULTURE. 



the tree by some scratch or bruise in the protecting bark which has exposed 

 the susceptible growing layer beneath to the visits of germ laden Insects. 



Thus we see that pear blight is caused by a germ to which the name Bacillus 

 amylovorus (Burril) has been given, the meaning of which is starch destroying. 

 We see that it is spread from one tree to another by insects, especially bees, 

 and that the germs may gain entrance into the plant in any of three ways: 

 First, and most important, through the blossom; second, through insect bites 

 in the tender shoots; third, through mechanical injuries to the bark of the 

 limbs and trunks of the trees. 



CONDITIONS FAVORING THE DISEASE. 



Although the knife is our only hope of exterminating the blight, there are 

 undoubtedly conditions which favor the disease. 



It is a matter of common observation that climatic conditions have a marked 

 influence; warm, moist weather with a large amount of rainfall favors it, while 

 bright, dry, cool weather tends to check it. That is, the former conditions are ad- 

 vantageous to the growth of the germs while the latter are unfavorable. 



High cultivation, rich soil, heavy manuring, the use of large quantities of 

 commercial fertilizer containing a great deal of nitrogenous material and heavy 

 pruning all tend toward the growth of tender, succulent shoots. It is in this 

 sort of plant tissue, gorged with sap, that the blight germs can grow and 

 multiply most rapidly. Biting insects whose mouth parts are contaminated 

 with the casual microbes, are most partial to these juicy shoots and leaves and 

 their bites often serve to infect the tree. 



It is evident, then, that vigorous, healthy, rapidly growing, too well cared 

 for orchards are more liable to the disease than others and since these are factors 

 which the grower can control, it is he who must strike the happy medium which 

 will not permit the trees to suffer and yet will not give ideal conditions for the 

 development of the germs. 



PBEVENTION AND TBEATMENT. 



The treatment of fire blight is of two kinds — the one, preventative, which 

 aims at making the tree resistant to the attacks of the disease; the other, 

 curative, which is intended to exterminate the harmful microbes and thus prevent 

 their spread. 



(1) It is obvious that if we are to render our trees resistant to blight, we 

 must avoid those conditions which increase the predisposition to the disease. 

 We have already mentioned the most potent factors in the propagation of blight 

 as high cultivation, rich manures, commercial fertilizer high in nitrogenous 

 material, excessive soil moisture and high pruning. In short, anything which 

 favors the rapid growth of tender, succulent shoots should not be practiced. 

 It is understood, of course, that these suggestions are not to be followed with- 

 out reason or the trees will suffer from troubles other than the blight. The 

 trees should be allowed to ripen their wood and to this end the grower must 

 use some means which will limit the moisture in the soil. It Is recommended 

 that some good cover crop such as oats be used for this purpose. 



(2) With a disease w^orking as this does in the juicy part of the stem between 

 the bark and the wood, there is no chance of reaching the trouble by means of 

 sprays for unless the chemicals come in contact with the bacteria, spraying is 

 futile. 



The knife and saw remain as the only effective remedies. We must cut out 

 and burn all affected twigs, leaves and branches not only from the pear but the 

 apple, quince and related species as well, so that there will be no infectious material 

 near by for bees to carry into the blight free orchard. It is very essential in 

 cutting out the diseased branches to cut well below the discolored part as the 

 bacteria are usually far below this region, the discoloration not appearing until 

 after the bacteria have been at work some time, so that even if all the blackened 

 wood were removed the seat of the trouble would not have been reached, and 

 the germs would live on in the apparently healthy stump, soon to cause another 

 visible outbreak of the blight. The affected branches should be cut back all 

 the way from ten to fifteen inches below the discolored wood and if the branch 

 be a large one, more than one-half inch in diameter, the cut surface should be 



