VEGETABLE AND FIELD CROPS 311 



mon leaf spot has almost precisely the general appear- 

 ance illustrated in Fig. 135, except that small pycnidia 

 occupy the spots. 



The disease attacks the older leaves first and works 

 toward the top of the plant, often causing the loss of so 

 many leaves as to give the plant the appearance of blight, 

 and resulting in complete ruin of the crop. The presence 

 of the leaf spot distinguishes this from any of the blights. 

 Spraying with Bordeaux mixture is effective against this 

 disease though valueless against the various wilts. 



Cylindrosporiose (Cylindrosporium sp.). — This disease 

 in general appearance, damage, and treatment resembles 

 septoriose. See above. 



Downy mildew, blight {Phytophthora infestans (Mont.) 

 DeBy.). — Arising from the same cause as the dreaded po- 

 tato blight, of which host the tomato is close kin, is the 

 very injurious tomato blight, causing complete devastation 

 of the crop in some sections, and resulting in a loss of many 

 thousands of dollars. It has been reported in Massachu- 

 setts, Colorado, and is serious in California. 



As is the case with the potato, the amount of damage 

 is closely dependent upon suitable weather conditions, the 

 disease being greatly favored by a warm, humid atmos- 

 phere. It appears suddenly as dark, discolored spots on 

 the fruit and other green parts. On the fruit the spot, 

 usually upon the upper side, is watery and large. Many 

 tomatoes, apparently healthy when picked, rot in shipment, 

 the rot being accompanied, under humid conditions, by 

 a fine, white surface mold. Dark spots upon stems and 

 branches soon extend throughout the whole plant, giving 

 it the appearance of one stricken by frost. 



