DISSEMINATION OF BACTERIAL WILT OF CUCURBITS 



[PRELIMINARY NOTE] 



By Frederick V. Rand, 

 Assistant Pathologist, Laboratory of Plant Pathology, Bureau of Plant Industry 



In the discussion of his exhaustive studies upon bacterial wilt of 

 cucurbits, Dr. Erwin F. Smith ^ makes the following statements relative 

 to certain still unsolved portions of the wilt problem: 



Leaf-eating insects, and especially Diabrotica vitiaia (fig. 55), are, I believe, the 

 chief agents in the spread of this disease. They feed readily, and sometimes the 

 writer has thought preferably (fig. 7), on wilted leaves which are swarming with this 

 organism. In this way their mouth-parts can not fail to become contaminated and 

 to serve as carriers of the sticky infection. No other means of dissemination is known 

 to the writer, and this is believed to be the common way in which the disease is dis- 

 tributed. * * * 



Seasonally the disease does not manifest itself until the leaf-eating beetles have 

 put in their appearance, and this has led to the suspicion that the organism might 

 pass the winter inside the bodies of these hibernating insects {Diabrotica vittata). As 

 to this nothing definite is known. 



He has referred to this subject again in his St. Louis address,^ as 

 follows : 



The writer has since proved several diseases to be transmitted by insects, notably 

 the wilt of cucurbits, and here the transmission is not purely accidental, but there 

 appears to be an adaptation, the striped cucumber beetle (Diabrotica vittata), chiefly 

 responsible for the spread of the disease, being fonder of the diseased parts of the plant 

 than of the healthy parts. This acquired taste, for it must be that, works great harm to 

 melons, squashes, and cucumbers. Whether the organism winters over in the beetles, 

 as I suspect, remains to be determined. Certainly the disease appears in bitten 

 places on the leaves very soon after the spring advent of the beetles. 



It was especially with a view toward throwing some light on the mode 

 of hibernation of the causal bacteria and of developing some practical 

 method of control that the writer undertook to continue the studies upon 

 this frequently very destructive disease. Since the study was begun in 

 midsummer (July, 1914), the first season's work consisted largely of 

 field observations which covered the territory from eastern Long Island, 

 N. Y., and Maryland to Indiana and Wisconsin. Some of the worst 

 examples of injury from wilt were found in eastern Long Island, and 

 accordingly this locality was selected for the field tests of the following 

 season (191 5). While further investigations are under way, it appears 



I Smith, Erwin F. Bacteria in Relation to Plant Diseases, v. 2, p. 215. Washington, D. C, 1911. 



2 . A conspectus of bacterial diseases of plants. In Ann. Mo. Bot. Gard., v. 2, no. 1/2, p. 390, 



Journal of Agricultural Research, Vol. V, No. 6 



Dtpt. of Agriculture, Washington, D. C. Nov. 8, 1915 



aw • G — 64 



(257) 



