220 Diseases of Truck Crops 



Benincasa cerifera, Cucurbita fcetidissima, C. call- 

 fornica, 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 vittatd). 



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. 



