220 Diseases of Truck Crops 



Benincasa cerifera, Cucurbita fcetidissima, C. cali- 

 fomica, Echinocystis lobata. 



Symptoms. The symptoms of bacterial wilt are 

 very striking. At first a few leaves of the plant are 

 wilted. Soon after the entire plant wilts and dies. 

 In cutting through an infected stem, a whitish viscid 

 exudate oozes out from the vascular bundles of the 

 cut surface. In placing one finger on the viscid 

 substance and then gently removing it, the bac- 

 teria will be strung out into numerous delicate 

 threads resembling cobwebs. The disease works 

 quickly and the change of leaf color from bright 

 to dull green is also sudden. Cantaloupes, unlike 

 squash, show no tendency to recover temporarily 

 from wilt. 



Bacterial wilt is spread about through the bites of 

 leaf-eating beetles, such as striped cucumber beetle, 

 (Diabrotica vittata). 



The Organism. B. tracheiphilus is a short straight 

 rod with rounded ends. The organism occurs singly 

 in pairs and rarely in chains of four; it is motile by 

 means of flagella. It grows slowly on gelatine which 

 is not liquefied. On potato cylinders growth is vigor- 

 ous, resulting in a gray-white film with no changes 

 manifested in the substratum. There is no gas pro- 

 duction and the organism is aeorobic. 



Control. Infection begins at a place of injury 

 produced by the bite or puncture of insects. Hence 

 any attempt at controlling wilt should first aim 

 at controlling insect pests. For further control, 

 see p. 232. 



