DISEASES OF PLANTS— SPRAYING 225 



as in the case of pear blight and peach yellows. (3) Those 

 due to poor drainage or poor soil or unfavorable climate; 

 these would not be contagious. 



Prevention of Plant Diseases. — The spores or organisms 

 from which the fungous diseases develop may be killed by 

 special spray materials. These should be killed before they 

 get into the leaves or other parts of the plants. Spraying is 

 a means of preventing disease rather than curing it. The 

 spray materials are made just strong enough to kill the dis- 

 ease germs and weak enough not to harm the useful plants 

 that are sprayed. (See Appendix for formulas of spray 

 mixtures.) 



Exercise. — Studying Plant Diseases. — Specimens of va- 

 rious diseases found on fruits, vegetables, trees, and other 

 plants may be brought to school. Let the pupils name all 

 of these possible. If there are any that seem to be serious 

 diseases in the neighborhood at the time they may be re- 

 ported or specimens sent to the State Agricultural Experi- 

 ment Station of that State. Ask that Station for special 

 bulletins telling how to control the particular disease. 



Brown Rot of Peaches. — This disease causes decay of 

 the fruit and the blighting of the twigs of peaches, plums, 

 and cherries. Fig. 142 shows the rot on peaches. The trouble 

 with peaches is confined almost exclusively to the early 

 varieties. After the rotted fruits have become dry they 

 cling to the trees, and thus hold the spores over until the 

 next year. Remove all such dried fruits from the trees in 

 the winter. The sprayings made to control San Jose scale 

 will help to keep this disease in check. 



Peach Scab or Black Spot. — This disease gives the fruit 

 a sooty appearance, because of the presence of grayish black 

 spots. The scab may become so bad as to cause the fruits 

 to crack open. It is thought that this disease is worse in 

 orchards where the air-drainage or ventilation is poor. 

 Spray with the self-boiled lime-sulfur mixture, given in the 

 15 



