162 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 6 



its use. Since it requires a dilution of spraying material containing 

 approximately 1 per cent of oil to be effective against the insects 

 further experiments were discontinued. According to our observa- 

 tions this acid did not increase the insecticidal qualities of the spray. 

 We were unable to test sulphuric acid in any of the formulae since 

 it always prevented the emulsification of the oil by the soap. 



The use of rosin or rosin oil should also be avoided. One brand of 

 commercial miscible oil contained a considerable percentage of rosin 

 oil and this, while not so injurious as sulphuric acid, burned the leaves 

 and fruit when used at 1 per cent of the oil contents. The use of 

 rosin oil in the home-made products always resulted either in great 

 damage or unfavorably. One sixth of 1 per cent used in a spray 

 containing 2 per cent of oil caused many more leaves to fall than 

 where the same amount of oil in a spray without the rosin oil was 

 used. When used in May on oranges 1| inches in diameter at 1 

 quart rosin oil to the emulsion required to make ^ of 1 per cent of 

 petroleum fuel oil for 200 gallons of water or | of 1 per cent of rosin 

 oil, large areas were scarred. This injury was usually found on the 

 lower part of the orange where the drop of spray had collected. Rosin 

 oil did not increase the insecticidal qualities as much as it was ex- 

 pected and since it costs about three times as much as the paraffine oil, 

 we strongly advise against its use. 



Experiments with another miscible oil, made on the same dates 

 and in the same groves, using exactly the same percentages of oil 

 as was used in the experiments with the above brands, gave only good 

 results. It did not burn the leaves nor fruit and did not cause an 

 excessive shedding of leaves in the winter. The analysis showed this 

 product to be free from sulphuric acid and rosin oil, and to contain 

 only such chemicals as were necessary for the proper emulsification 

 of the oil used in its manufacture. 



Much work was done with emulsions of petroleum fuel oil 24** 

 Baume, distillate or gas oil 28° Baume, and two paraffine oils of 24° 

 and 28° Baume, respectively. The extensive use of these oils at 

 proper strengths did no immediate damage to the foliage or fruit. 



While it is a fact that oil sprays made without injurious chemicals 

 and used properly cause no immediate damage and never any serious 

 injury, they apparently interfere to a limited extent with the physio- 

 logical processes of the tree. On March 30 and 31, 1911, a row of 

 about 20 trees each was sprayed with petroleum fuel oil 1 per cent, dis- 

 tillate oil 1| per cent, paraffine oil 28° Baume 1 per cent, and paraffine 

 oil 24° Baume 1 per cent. At the time of the appUcation the leaves 

 were the new ones of the first spring growth and had not become 

 very green but were of a light yellowish green color. 



