1915] 



SMITH BACTERIAL DISEASES OF PLANTS 



399 



Great Britain and Germ 



Potato rots are probably the 



most destructive bacterial diseases. j 



France and Italy. — Potato diseases are common, 

 tubercle, common also in California, and all around the Medi 



Olive 



terrar 



is prevalent in spots 



Vine dise 



lly 



Maladie d'Oleran and crown-gall, do considerable damage. 

 Pear blight seems to be absent in France, but has been re- 

 ported from several places in Italy. The destructive Italian 

 rice disease, brusone, is not due to bacteria as reported, but 

 to a fungus {Piricularia) . 



METHODS OF CONTROL 



In conclusion, some words on prophylaxis will be in order. 

 Until recently almost nothing was known. Unfortunately so 

 far as regards most of these diseases, methods of control must 

 still be worked out. But with rapidly increasing knowledge 

 of the biological peculiarities of the parasites causing these 

 diseases, and of the ways in which they are disseminated, light 

 begins to dawn, so that before many years have passed we 

 may confidently expect the more intelligent part of the public 

 to be applying sound rules for the control of these diseases 

 rules based on the individual peculiarities of the parasites and 

 carefully worked out experimentally by the plant pathologist. 



The little that we now know may be summarized in part as 



follows : 



Waite has shown that pear blight winters over in excep- 

 tional trees on trunk and limbs in the form of patches which 

 ooze living bacteria the following spring and are visited by 



bees and other insects, and that if these "hold 



spots 



are cut out thoroughly over regions several miles in diameter 

 (wide as a bee flies), the disease does not appear on the blos- 

 soms and shoots the following spring, except as it is intro- 

 duced into the margins of this area from remoter uncontrolled 

 districts. He has tried this method of control very success- 

 fully, both in Georgia and California. Sometimes only one 

 tree in many carries over the disease, but such is not always 

 the case, and the success of this method involves the inspec- 

 tion of every pome tree in a district with complete eradication 



