TOMATO DISEASES 135 



The fungus that causes early blight of potatoes 

 (Alternaria solani (E. & M.) J. & G.) occurs on to- 

 matoes also, sometimes doing much injury. The spots 

 formed are at first small and black, later enlarging 

 and exhibiting fine concentric rings. 



A somewhat similar leaf-blight results from a spe- 

 cies of Cylindrosporium, and other fungi may occur 

 on diseased leaves. 



Leaf mold (Cladosporium fulvum Cke.) is quite 

 distinct from the foregoing in appearance. It does 

 not cause such distinct spots but occur-s in greenish 

 brown, velvety patches of irregular outline on the un- 

 der side of the leaves. The lower leaves are first at- 

 tacked, and as the disease progresses they turn yellow 

 and drop off. This is the principal fungous enemy of 

 greenhouse tomatoes, but also does injury in gardens, 

 particularly in Florida and the Gulf region. It is read- 

 ily controlled by spraying. In the greenhouse care 

 should be taken to ventilate well, without, however, al- 

 lowing cold drafts to strike the plants. 



Downy mildew (Phytopthora infestans DeBy.), the 

 cause of the late blight of potatoes, will attack toma- 

 toes during cool and very moist weather, which greatly 

 favors its development. Such outbreaks sometimes 

 occur to a limited extent in New England and serious 

 losses are reported on the winter crop in southern 

 California, but the disease has never been troublesome 

 in other sections of the country, as it cannot develop 

 in dry or hot weather. It affects the tomato as it does 

 the potato, forming on the leaves dark, discolored 

 spots, which spread rapidly under favorable condi- 

 tions, killing the foliage in a few days. The fruit is 



