68 BACTERIAL DISEASES OF PLANTS 



searched for in that country. It was not observed in the wheat 

 region West of the JNIississippi River until after numerous im- 

 portations of Russian wheats. 



METHODS OF CONTROL 



In conchision, 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. 

 In the United States within a generation every large crop 

 establishment will have its plant pathologist. The little 

 that we now know may be summarized as follows : 



Waite has shown that pear blight winters over in excep- 

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

 ooze living bacteria the following spring (see Figs. 282, 283) 

 and are visited by bees and other insects, and that if these 

 "hold-over" spots are cut out thoroughly over regions several 

 miles in diameter (wide as a bee flies), the disease does not ap- 

 pear on the blossoms and shoots the following spring, except 

 as it is introduced into the margins of this area from remoter 

 uncontrolled districts. He has tried this method of control very 

 successfully, both in Georgia and California. Sometimes only 

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

 the case, as Sackett has shown, and the success of this method 

 involves the inspection of every pome tree in a district, with 

 complete eradication of every case of the hold-over blight, and 

 this in great fruit regions requires a small army of trained 

 inspectors. During the blighting period in late spring and 

 early summer, if one would save his orchard, the trees must be 

 cut over for removal of diseased material as often as every 

 week, and in the worst weather oftener. Furthermore, some 



