102 PLANT GROWTH 



ease in your yard or from your neighbors' yards. Copper and 

 sulphur compounds are very effective poisons for most dis- 

 ease-producing organisms. Bordeaux mixture^ is very widely 

 used, but must be mixed at each appHcation for best results. 



Much time and effort is saved by mixing a stomach 

 poison, a contact poison, and a fungicide together and using 

 each time, because it will usually keep all the pests under 

 control. The first insects and the first spores will be killed, 

 preventing their reproduction. 



Spraying may be considered a cultural treatment as well 

 as a protection from insects and diseases. Tests made re- 

 peatedly with potatoes showed an increase in yield that more 

 than paid for the spraying when the unsprayed plants had 

 neither insect injury nor disease. A stimulation will be 

 shown on many plants if they are sprayed and compared 

 with unsprayed ones. Spraying is not a fertilizer, but it is 

 believed to influence photosynthesis and decrease transpi- 

 ration. 



In order that effective work may be done spraying should 

 be made as simple as possible. The leaf is more effectively 

 covered as the spray becomes a finer mist; this is controlled 

 chiefly by increasing the pressure. The larger power sprayers 

 often use pressures as high as four hundred pounds per 

 square inch, but with hand sprayers such pressures are im- 

 possible. However, if a sprayer is selected according to the 

 number of plants to be sprayed more time can be used per 

 plant with a smaller sprayer. The lower leaf is difficult to 

 cover with the spray but it is the part that is most susceptible 

 to infection because it retains moisture and because many 

 species have more stomata on this surface. Therefore, the 

 sprayer must have provision for effectively throwing the 

 spray upward. 



1 Bordeaux mixture is usually used as a "5-5-50" mixture. Five pounds of copper 

 sulphate should be dissolved in water and diluted to 25 gallons, and five pounds burned 

 (unslaked) lime should be slaked to make a creamy mass, after which it should be 

 diluted to 25 gallons. The two should be mixed and used fresh. If it stands some 

 settling will occur. 



