74 BACTERIAL DISEASES OF PLANTS 



which resembles a land-drag but is made of steam pipes, the 

 teeth as well as the frame-work being hollow. The teeth are 

 pointed and perforated with small holes so that when they are 

 driven into the ground and live steam turned on it escapes and 

 permeates the entire soil. I have seen the soil of lettuce houses 

 in New England freed from parasites in this way. (Made by 

 Geo. M. D. Sargent, Belmont, Mass.) 



On badly infested fields, whatever the disease, a careful 

 rotation should be practised and low places should be drained. 



Certain diseases may be held in check by germicidal sprays. 

 Newton B. Pierce reduced the number of infections in walnut 

 blight in California 50 per cent by this method, using Bordeaux 

 mixture. Scott and Rorer combated leaf-spot of the peach 

 in this way using self-boiled lime sulphur, the sprayed trees 

 retaining their leaves, the unsprayed ones becoming defoliated. 

 G. Bellini in Italy has recommended Bordeaux mixture and 

 used it successfully on olive trees, following hail-storms, to 

 keep out the olive tubercle. 



When, as in case of the cucurbit wilt due to Bacillus trach- 

 eiphilus, diseases are transmitted by insects, destruction of the 

 latter must receive prompt attention. Trap crops may be 

 used. 



Great care should be taken to keep the manure heap free 

 from infection. Diseased rubbish should be burned or buried 

 deeply. It must not be thrown into a water-supply or fed to 

 stock or dumped into the barnyard. Diseased potatoes and 

 other crops should be cooked before feeding to animals. 



One of my fancies is that plant pathologists will eventually 

 discover competing saprophytes which when sown on infected 

 soils will overcome and render harmless certain of the bacterial 

 parasites present in them. We have some evidence that nature 

 does this, and man working toward a definite end should be able 

 to improve on nature. 



Wet fields should be drained and, in general, every effort 

 should be made to put the crop under good growing conditions, 

 i.e., to give it a proper soil, good food, the right climate and 

 the right amount of soil moisture. A wise rotation should 

 also be practised. Rotation is the keynote of successful agri- 



