SPRAYING FOR CITRUS INSECTS AND MITES IN FLORIDA. 17 



While both the fish-oil soap and the oil emulsions are ettective 

 in killing the white flies and scale insects, experience indicates that 

 the latter are far superior to the former under Florida conditions. 

 This superiority is due to the physical properties of the oils. The 

 high boiling point and great viscosity possessed by these oils make 

 them operative over a longer period of time after application, and, 

 too, they are only slowly affected by average temperatures and 

 showers. Foliage sprayed with miscible oils remains slightly oily in 

 appearance and to the touch for several weeks after spraying. Fish- 

 oil soap leaves no such evidence that the trees have been sprayed. 

 The oil spray is much less affected by showers than is the fish-oil-soap 

 spray. Summer showers falling after the oil spray has once had 

 an opportunity to dry on the foliage have little effect in lessening the 

 efficiency of the spray. Such showers, however, have a very evident 

 effect upon the number of insects killed by the soap spray. The 

 effectiveness of the weaker strengths of fish-oil soap is much more 

 reduced by showers than is the effectiveness of the weaker strengths 

 of oil sprays. 



In experimental work on a large scale for the control of the citrus 

 white fly the miscible-oil sprays have given better results than have 

 the soap sprays. This greater efficiency seems to be due, not to a 

 higher percentage of larvae and pupae killed when the spray is ap- 

 plied, but to the effect that oil sprays exert upon unhatched eggs or 

 upon the young larvae hatching from them within 10 to 14 days after 

 spraying. The oil forms a film over the eggs which prevents a large 

 percentage from hatching, and the young larvae from those which do 

 hatch are killed either in the act of emerging from the shell or in 

 crawling over the oil-coated leaf. Those who are in touch with the 

 white-fty problem appreciate the fact that no matter how efficacious 

 an insecticide may be, in killing larvae and pupae on the leaves at the 

 time the spray is applied, if it does not either kill these unhatched 

 eggs or remain operative long enough to kill the larvae that subse- 

 quently hatch, much of the benefit of spraying is counterbalanced b}^ 

 reinfestation. 



There are two ways of making miscible-oil emulsions: (1) Without 

 heat; (2) with heat. The first is called the "cold-stirred emulsion"; 

 the second, the " boiled " emulsion. Both kinds of emulsion are 

 efficient, reliable, and easily made. 



COLD-STIRRED EMULSION. 



Formula. 



Fish-oil soap: 



By weight pounds 8 



By measure jrallon__ 1 



Paraffin oil, 24 or 28 Baume gallons.. 2 



Water gallon 1 



32654 18 Bull. 933 3 



