8 CIRCULAR 2 7 0, U. S. DEPARTMENT OF AGRICULTURE 



by the manufacturers. If lime-sulfur solution must be used for the 

 control of scab or powdery mildew, it may be combined with the lead 

 arsenate. The lime-sulfur should be put into the tank while it is 

 being filled, and the lead arsenate added just before beginning to 

 spray. The mixture should be used at once on account of a chemical 

 reaction which occurs. This reaction may be retarded by putting 

 casein spreader or hydrated lime into the tank before the other mate- 

 rials are added, using them at the rate of 1 pound to 100 gallons of 

 spray. 



Residues of arsenic or lead, in quantities sufficiently great to con- 

 stitute a menace to the health of the consumer, must be removed by 

 washing or wiping before the fruit is sold. Although this is not ordi- 

 narily difficult, 4 the grower should avoid spray schedules that may 

 result in excessive residues. Calcium arsenate, which contains no 

 lead, may be used for light infestations, although this material may 

 cause burning and does not usually control as well as lead arsenate. 



Mineral-oil emulsions (p. 72) are very valuable for controlling the 

 codling moth if used in conjunction with the arsenical or some other 

 material. Enough emulsion should be used so that the diluted spray 

 contains from one-half to three-fourths of 1 percent of actual oil, 

 and not more than four applications should be made in a season. 

 The type of oil to use is explained on page 72. Oil emulsions may 

 cause a severe drop of fruit and foliage if applied on trees that have 

 received sulfur sprays within 2 months. Therefore, when the use of 

 sulfur sprays is necessary for the control of apple powdery mildew or 

 other fungous diseases, oil cannot be used with safety in the early 

 cover sprays. Oil may be used most effectively when most of the 

 eggs are on the trees, since its chief value lies in its ability to destroy 

 eggs. It will generally be most valuable if added to the second and 

 third cover sprays for the first brood, and to one or more sprays for 

 the second brood. Since it also causes the lead arsenate to adhere 

 more firmly to the fruit and foliage, there will be difficulty in remov- 

 ing the spray residue if the combination of oil emulsion and arsenical 

 is used in the second-brood sprays. In place of the arsenical, nicotine 

 sulfate (40 percent nicotine) may be combined with the oil emulsion, 

 using it in the proportion of two-thirds to 1 pint to 100 gallons of 

 spray. Since this combination interferes greatly with residue removal, 

 not more than two or three applications of lead arsenate should be 

 made preceding its use. If the infestation is light, especially if pears 

 are to be sprayed, it may be sufficient to use this combination of 

 nicotine sulfate and oil emulsion for all the cover sprays. 



In the arid valleys cryolite (sodium fluoaluminate) , in the propor- 

 tion of 3 pounds to 100 gallons of water, may be used in the cover 

 sprays. This material should not be used alone but only in conjunc- 

 tion with an oil emulsion or with fish oil. One pint of the latter to 

 100 gallons of spray is the most satisfactory addition to cryolite. Ex- 

 cessive residues from this material must be removed by wiping or 

 washing the fruit before it is marketed. 



4 Detailed instructions for removing spray residues may be found in Farmers' Bulletin 1752, Spray-residue 

 Removal from Apples and Other Fruits. 



