18 BULLETIN 837, U. S. DEPARTMENT OF AGRICULTURE. 



almost complete for both materials on the Ives and Concord varie- 

 ties. On the Catawbas the arsenate of calcium averaged 90 per 

 cent control and the arsenate of lead 96 per cent, but the checks 

 adjacent to the arsenate of calcium plats were 12 per cent more 

 heavily infested than those adjacent to the arsenate of lead plats 

 so the comparisons are very close. These results may indicate that 

 the arsenate of lead adhered slightly longer in the season than the 

 arsenate of calcium. In recording the spray residue on the fruit 

 at harvest time, slightly less was found on the arsenate of calcium 

 plats than on corresponding arsenate of lead plats. This feature 

 is an advantage in grape-berry moth spraying and is discussed 

 later. No foliage injury that could be attributed to the arsenical 

 occurred on any of the arsenate of calcium plats. 



Grape spraying experiments were continued in 1919 and foliage 

 injury occurred on all plats of 'the Ives variet} T where commercial 

 arsenate of calcium was used at the rate of 1J pounds to 50 gallons 

 of water with 3 pounds of freshly burned stone lime slaked and 

 added to each 50 gallons of spray solution. This experience indi- 

 cates that the use of arsenate of calcium on the Ives variety is unsafe. 



ARSENATE OF CALCIUM, HOME-MADE PASTE. 



Varied success had been reported from the use of home-made 

 arsenate of calcium pastes as sprays for fruit trees. To determine 

 the efficiency of these home-made materials for use in sprays on 

 grapes the following experiments were conducted. Pastes were 

 made according to the following formulas and methods and applied 

 in spray solutions to grapes: 



(1) Arsenate of soda + stone lime. 



Sodium arsenate, fused (dry powdered) 60 per cent 



As 2 Oo ounces— 30 



Stone lime do 18 



Water do 48 



Total do 96 



The sodium arsenate was dissolved in the water and the resultant 

 solution used to slake the lime. A smooth paste arsenate of calcium 

 of about 18 per cent As 2 3 content resulted. This was decanted 5 

 times to remove the sodium hydroxicl. The resultant paste was 

 used at the rate of £§ pounds to 50 gallons to be comparable with 

 arsenate of lead (commercial powder 30 per cent As 2 5 ), 1^ pounds 

 to 50 gallons. 



(2) Arsenic acid + stone lime. 



Arsenic acid (liquid) 78 per cent As 2 B ounces— 10 



Stone lime do 8 



Water do 34 



Total do 52 



