6o6 BACTERIA IN RELATION TO PLANT DISEASES 



lar occupant.' Smith^ proved that the striped cucumber beetle, Diabrottica viator, 

 transmits B. tracheiphilus, the pathogen of cucurbit wilt, and Rand,-' Enlows, and 

 Cash have presented strong evidence that the organism winters over only in the in- 

 testinal tract of certain of these beetles. Leach"* reports the seed-corn maggot {P/ior- 

 bia fusciceps) as an agent of dissemination, inoculation, and hibernation of B. atro- 

 septicus, and that the organism is necessary for the normal development of the larvae. 

 This work has not been reported in detail, nor has it been repeated by other investi- 

 gators. 



CONTROL OF BACTERIAL PLANT DISEASES 



Investigations in and practice of control of bacterial plant diseases constitute a 

 very considerable part of the activity of plant pathologists. The control measures 

 practiced are determined by the biology of both host and pathogen. 



In many instances in which bacteria hibernate on or in plant organs such as seeds, 

 tubers, roots, and stems, disinfection by heat (wet or dry) or chemicals (organic and 

 inorganic) is resorted to. Similar methods are used in sterilizing soils. Selection of dis- 

 ease-free organs or plants is also found useful. Spraying plants with germicidal sub- 

 stances is effective in some cases. Crop rotation, proper timing of the planting so as 

 to avoid environmental factors such as temperature, moisture, etc., optimum for the 

 pathogen, and field sanitation, i.e., destruction of plant debris on which the pathogen 

 can be carried over, are employed with success. Eradication of diseased plants or 

 plant organs is a generally practiced method, and associated with it are local, state, 

 and federal quarantine measures. 



In the diseases which are overwintered and disseminated by insects primarily, 

 the main task is to destroy the insect. 



Since many plant pathogens enter only through wounds, care to control the agen- 

 cies that break the protective surfaces of plants becomes imperative. 



Finally, the development by selection and crossing of resistant varieties promises 

 to become one of the most important and economical control measures. 



'Petri, L.: Centralbl.f. Bakteriol., Abt. II, 26, 357. 1910. 



' Smith, E. F.: Bacterial Diseases of Plants. 



3 Rand, F. V.: "Insects as Disseminators of Plant Diseases." Phytopath., 12, 225-28. 1922. 



"Leach, J. G.: "The Relation of the Seed-Corn Maggot to Potato Blackleg," /^/(/., 16,68. 1926. 



