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Tomato-Leaf Rust. 



[FEB., 



The destructive disease known as tomato-leaf rust, due to 

 the parasitic fungus Cladosporium fulvum, Cooke, was first 

 described by Dr. M. C. Cooke, from 

 Tomato-Leaf specimens received from North Carolina 

 Rust. in l88 3- 



Its occurrence in this country was re- 

 corded by Plowright in 1887, when it proved very destructive 

 to tomatoes grown under glass, in two different districts. 

 Curiously enough, the fungus was not observed as a source 

 of injury to tomatoes in the United States until the year 1888. 

 It is now a well-known pest, attacking tomatoes in France and 

 Italy also. 



The leaves, stem, and occasionally the fruit, are attacked. 

 The fungus usually first appears on the leaves, in the 

 form of small scattered spots, which gradually increase in 

 size and encroach on each other, until almost the entire under- 

 surface of the leaf becomes covered with a minutely velvety, 

 dull rust-coloured layer, consisting of the spore-bearing por- 

 tion of the fungus, the spawn or mycelium being imbedded 

 in the tissues of the leaf. The presence of the fungus is first 

 indicated by the appearance of pale yellowish patches on the 

 upper surface of the leaf, corresponding in position to infected 

 areas on the under surface. These yellowish patches increase 

 in size, in proportion to the spread of the fungus on the 

 under surface, and gradually change through brown to almost 

 black, often with a tinge of purple. The fungus forms long, 

 rust-coloured, afterwards blackish streaks on the stem, and 

 more or less circular, scattered patches on the fruit. When the 

 fungus shows a rusty tinge, the leaves wilt and soon die, and 

 as a rule the disease spreads very quickly. This, to a very 

 great extent, is due to the usual method of spraying horizon- 

 tally, so that the spores are forcibly driven from one plant to 

 another. If by any means the water could be allowed to fall 

 from above, after the manner of a steady rain, numerous 

 spores would be washed on to the soil, where they would ger- 

 minate and perish, instead of being lodged on the leaves of 

 healthy plants, where they set up new centres of disease. 



Spraying with fungicides is of very little avail, unless com- 

 menced the moment the disease first shows on the foliage. 

 The reason for this is that no fungicide is a curative agent ; 



