34 FARMERS ' BULLETIN 933. 



or twice as much as required, has been used extensively without caus- 

 ing normal leaves to fall prematurely. In small tests 3 per cent of 

 oil in the diluted spray material caused no damage. No injury 

 follows spraying either before or during a rain and neither does 

 humidity appear to be a factor in causing injury. When the oil 

 emulsions are used, whether made of kerosene or heavy lubricating 

 oil of 24 Baume, shadows sometimes appear on the fruit. These 

 shadows usually follow spraying during hot, bright days when the 

 temperature is above 91 or 92 F. As the temperature is very 

 high, the heat evaporates the water in the spray material before it 

 has had time to run off. This concentrates the oil in one spot and 

 causes a slight damage to the stomata, resulting in a darker shade 

 of green than the surrounding area. These dark-green shadows 

 disappear not later than a week or two after the fruit has colored 

 in the fall and it is impossible to locate the previous discolora- 

 tions if these have not been marked. Sometimes the damage is 

 localized to the spot where the drop of spray has collected. The 

 only way to avoid such damage would be to cease spraying when the 

 temperature rose above 92. This injury occurs only occasionally. 



The application of the oil sprays two or three times a year at 

 the recommended strength has never been known to cause devitali- 

 zation of the trees. If an excessive amount of spray is used the nor- 

 mal growth of the leaves is interrupted. They do not reach the 

 proper size, become thin, and the tree has the appearance of being 

 stunted. The fruit also is small, does not color up properly or at the 

 proper time, and is sour when other fruit is sweet. Such a condition 

 only follows the application of from three to six times as much oil 

 as the worst infestation of white flies and scale insects requires. Two 

 applications within one month of a 2 per cent solution in 1916 did 

 no noticeable damage to either the tree or the fruit. 



Soda-sulphur solution very seldom, if ever, causes any damage to 

 the trees or fruit. No accumulated ill effects have been known to 

 follow the use of this spray. This noninjuriousness is no doubt due 

 to its lack of stability since it is easily washed off by rains and dissi- 

 pated by dews. 



Lime-sulphur solution does not cause damage at the recommended 

 dilutions under average conditions. When the temperature is 92 

 F. and the sun is bright, injury to the fruit sometimes follows, but 

 this does not often occur. In all the experimental work such in- 

 jury followed on only one occasion. The injury is always located on 

 the side of the fruit turned to the sun at the particular time of day 

 when the spraying was done. The exact cause of this type of injury 

 is not yet fully understood, but it is very certain that it should not 

 be considered as being due to the insecticide alone, but to the com- 

 bined action of the sun and the insecticide. When the injury is 



