134 INSECT PESTS 



hate it is carbolic acid. They vanish like magic at its 

 appearance. But so also does plant life in general ! 

 Are we able then to administer this dose in such a way 

 as to avoid injury to the crop itself ? The safest form 

 in which to apply the acid is as an emulsion with soap 

 and as a soil dressing on the vacant field before the plants 

 are put in. The carboHc treatment is, however, a drastic 

 one which need only be brought into play in very bad 

 cases. 



A much better scheme, for general use on a large scale, 

 and which obtains the same result at less cost, is to 

 spread the ground evenly with powdered quicklime a 

 month or so before the plants or seeds are to go in. 

 This has the double advantage of improving the ground 

 and warding off fungi spores. Whence it follows that 

 it is on the well-managed soils that plants escape these 

 things, giving them that rapid and vigorous growth which 

 is unfavourable to the germination of parasitical diseases. 



I now propose to take a short general survey of the 

 common fungi which attack fruit and vegetable crops. 

 The subject is a big one, and I can only deal with it 

 in the briefest way within the limits at my disposal. 



Among field and garden crops the potato comes first. 

 The dangerous exotic, as it has been called, is subject 

 to some fifteen or twenty fungoid diseases in all, the most 

 prevalent being : 



Potato disease, Wart disease, Corky Scab, Dry Rot, 

 Skin Spot, Leaf Curl, Silver Scurf and Rust. 



The first-mentioned, known to the botanist as Phyto- 

 phthora infestans and to the farmer as " bhght," has 

 the general appearance on the leaf shown on Plate 31, the 

 appearance of the fungus itself under the microscope 

 being also indicated. 



As a matter of fact Potato Bhght has had a very im- 

 portant effect on English history. Possibly, if it were 

 asked, who brought about Free Trade, nine out of ten 

 people would answer " Richard Cobden," which would 



