1897.] PUBLIC DOCUMENT — No. 33. 75 



The Tomato Mildew (^Cladosporium fiilvmn^ Cke.). 



The disease which is commonly called mildew is without 

 doubt one of the greatest obstacles to success in growing 

 tomatoes in the hot-house. While it does not always kill 

 the vines outright, still, its effect in weakening their vitality 

 and reducing their yield is a most serious one. We have 

 received specimens of tomato leaves affected by this disease 

 from several different localities, and have observed it in 

 greater or less abundance in almost every house of tomatoes 

 which W'C have examined. It also attacks tomatoes grown 

 out of doors, but by no means so generally as in the hot- 

 house. 



When this disease comes on, there appear on the lower 

 surface of the leaves brownish, felt-like spots of irregular 

 shape and various sizes, which rapidly increase in extent, 

 until the whole leaf finally turns black and withers away. 

 It does not always spread so rapidly and kill the leaves at 

 once, but is often found only on the lower leaves, or in spots 

 which do not increase ra})idly in size. Nevertheless, it is 

 constantl}^ weakening the plant, and, let a favorable oppor- 

 tunity come, as come it will sooner or later, and it spreads 

 through the house with great rapidity and destructiveness. 



The fungus consists of a dense mass of thread-like fila- 

 ments, which ramify through the leaf in all directions and 

 more or less upon its surface. The felt-like areas on the 

 under surface of the leaves are composed of a mass of spores 

 and the filaments which produce them. The spores germi- 

 nate readily in water, developing filaments similar to those 

 from which they w'ere derived. This species belongs to a 

 group of fungi which are mostly moulds and mould-like 

 forms, growing upon dead vegetable matter or plants in a 

 weak and unhealthy condition. This mildew^ is especially 

 active in attacking such plants, upon which it produces the 

 above-described disastrous effect. Its development is also 

 greatly favored by excessive moisture in the air, i. e., a 

 "muggy" atmosphere, which indeed is favorable to the 

 development of most plant diseases. The tomato requires 

 a considerable heat for successful growth in the hot-house. 

 If, while the plants are growing rapidly, the temperature 



