42 LESSONS IN AQBICULTUBE 



LESSON XII 



PLANT DISEASES 



Injury and control. Perhaps we have noticed during 

 the summer that some of the plants we were interested 

 in grew sickly and died, in spite of all the care and 

 attention we gave them. We are told by the botanists 

 that plants have diseases, just as people do. Rust, 

 blight, smut, rot, and the like, are the common names 

 of diseases which afflict the plant. They spread from 

 plant to plant by means of little dust-like particles 

 called spores. These spores float around in the air and 

 settle on healthy plants. Here the spores may grow 

 and injure the plant by living upon its sap. They 

 must be destroyed or they may kill the plant upon 

 which they feed. The various diseases caused by the 

 spores are called fungous diseases. Some of the most 

 common forms are the fire blight of the pear and apple, 

 the smut of corn and oats, the rust of wheat, the potato 

 scab, potato blight, peach leaf curl, apple scab, club 

 root, black knot of plum, brown and bitter rot, and 

 many other kindred varieties. 



As soon as the diseases make their appearance in the 

 orchards or on the crops, the farmer should begin his 

 fight. If the leaves of the trees begin to dry up and 

 blacken with the blight, the affected parts should be 

 immediately cut off, at some distance below the blight, 

 and burned. The lime-sulphur, or Bordeaux mixture, 

 spray described in Lessons 11 and 64, are the spray 

 remedies to use on most plant diseases. 



