74 Diseases of Truck Crops 



foliage, and fruit. The writer knows of cases where 

 large areas of tomatoes, cantaloupes, and watermelons 

 were totally nained by hail. With the sweet potato 

 hail does not always ruin the crop, but it retards it. 

 The foliage and vines dry up as a result of the me- 

 chanical cutting and bruising from hail, but new 

 growth soon follows. Even when hail does not ruin 

 a crop, there is danger of infection at the place of 

 each cut or bruise (fig. ii). If "the affected crop 

 is valuable and shows promise of recovery, it shotdd 

 be sprayed with a good standard fungicide. 



LIGHTNING INJURY 



Injuries to trees from lightning are familiar to 

 aU. Jones and Gilbert' record an interesting case 

 of lightning injury to potato plants. The injury is 

 noticed in rotmd spots in the field (fig. 12 a), the 

 spots varying from ten to twenty feet in diameter. 

 The potato tops appear broken and disheveled 

 and upon drying off, within twenty -four hours 

 they wilt and die. In examining the individual 

 plant we find that the stem collapses and the top 

 falls over, the stem browns and shrivels faster above, 

 and less rapidly below this point. The pith at this 

 region browns and collapses, leaving a hoUow stem, 

 but without any softening such as usually occurs 

 with blackleg. No evidence of splitting or mechan- 

 ical rupture of the stem has been observed. Light- 

 ning injury may occur when thunderstorms are very 



' Jones, L. R., and Gilbert, W. W., Phytopath. 5 : 94-101, 1915. 



