Z CIRCULAR 5 9, IT. S. DEPARTMENT OF AGRICULTURE 



The investigations have been conducted throughout with the pur- 

 pose of devising safe methods for cleaning apples and pears satisfac- 

 torily to the world tolerance of 0.01 of a grain of arsenic as arsenic 

 trioxide per pound of fruit. The suggestions in this circular are 

 made with this tolerance in view. 



The summarized suggestions for the removal of spray residue 

 from the fruit will be given under the following headings:' (1) Gen- 

 eral aspects of spray-residue removal, (2) cleaning fruit by wiping 

 or brushing, and (3) cleaning fruit by solvent methods. 



GENERAL ASPECTS OF SPRAY-RESIDUE REMOVAL 



Plans for cleaning spray residue from the fruit should start with 

 the beginning of the spraying program. 



Experience has shown that there are a number of important vari- 

 ables which may affect the quantity and character of the spray 

 residue on the fruit at harvest time. Among them are the type and 

 concentration of lead arsenate used, the materials used in combina- 

 tion with the lead arsenate, the method and dates of applying the 

 sprays, and the weather conditions through the season. 



The number of applications and the strength of arsenate of lead 

 used should be reduced to the minimum required for the satisfactory 

 control of the codling moth. In this connection, the attention of 

 growers in Washington is referred to the spray recommendations 

 prepared for that State in 1928 by the representatives of the Wash- 

 ington Agricultural Experiment Station, the United States Bureau 

 of Entomology, and the Washington State Department of Agricul- 

 ture. Growers in Oregon are referred to Extension Bulletin 403 

 (1928 revision) on the orchard-spray program for Oregon. 2 



In a general way, experience has shown that in the Pacific North- 

 west apples and pears sprayed more than three times with lead 

 arsenate in concentrations of not over 2y 2 pounds to 100 gallons of 

 water will usually require a washing treatment in order consistently 

 to reduce the quantity of arsenic in the spray residue below the world 

 tolerance for arsenic. 



The greater the number of applications and the later in the season 

 these applications are made the greater will be the quantity of spray 

 residue on the fruit at harvest time and the more difficult will be the 

 cleaning problem. 



The use of spreaders with the lead arsenate in spraying has not 

 resulted in making the residue more easily removed by washing 

 methods unless the spreaders contained hydrated lime. Even then 

 the results have not always been consistent. The dry cleaning of 

 fruit seems to be slightly facilitated by the use of spreaders with the 

 lead arsenate, mainly because of the smaller number of heavy blotches / 

 of residue on the fruit. 



When certain grades of oil spray, especially the heavier types of 

 oil, are applied in combination with or after heavy applications of 

 lead arsenate the combined residue will generally interfere with 

 cleaning. The proper use of the correct type of oil with the lead 

 arsenate should prevent difficulty in satisfactorily washing fruit in 



2 Mote, D. C, and Zeller, S. M. orchard spray program for Oregon. 192s revision. 

 Oreg. Agr. Col. Est. Bui. 403, 22 p., illus. 1928. 



