22 



BULLETIN 5*71, IT. S. DEPARTMENT OF AGRICULTURE, 



Spraying experiments were conducted during the summer of 1915 

 for the purpose of determining the effects of various forms of lead 

 arsenate on pecan foliage. The pecan trees selected were 12 years 

 old and of a good size for their age. The spray material was very 

 thoroughly applied by means of a gasoline-power outfit, using a pres- 

 sure of about 200 pounds. Table XIX shows the results of this 

 work. 



Table XIX. — Spraying experiments against the larvse of the pecan leaf case-bearer at 



Monticello, Fla., in 1915. 



Plat 

 No. 



Num- 

 ber 

 trees. 



Treatment. 



Date of 

 applica- 

 tion. 



Ptesults. 



Degree of infes- 

 tation. 



Extent of arsenical injury 

 to foliage. 



I 

 II 



18 

 18 

 12 

 12 



5 



7 



Powdered lead arsenate lh 

 pounds, plus 3 pounds of 

 lime to 50 gallons of water. 



Powdered lead arsenate 1 

 pound, plus 3 pounds of 

 lime to 50 gallons of water. 



Paste lead arsenate 3 pounds, 

 plus 3 pounds of lime to 50 

 gallons of water. 



Paste lead arsenate 2 pounds, 

 plus 3 pounds of lime to 50 

 gallons of water. 



Paste triplumbic lead arsenate 

 2 pounds, to 50 gallons of 

 water. 



Paste triplumbic lead arsenate 

 2 pounds, plus 3 pounds of 

 lime to 50 gallons of water. 



1915. 

 Aug. 24 



...do 



Practically none. 

 do 



/ 



Foliage in good condition; 

 no appreciable burning. 



Do. 



III 



Aug. 25 

 ...do 



do 





IV 



do 



rather serious. 



V 



..do 



do 



verely burned; but the 

 trees did not shed their 

 leaves prematurely. 

 Foliage rather seriously 

 burned, especially mar- 

 gin of leaves. 



VI 



...do 



do 









no appreciable burning. 



As shown in Table I, the pecan leaf case-bearer was controlled 

 satisfactorily on all plats, but only on Plats I, II, and VI was the 

 spraying accomplished without appreciable arsenical injury to the 

 foliage. Maximum burning of foliage occurred on Plat V, where tri- 

 plumbic arsenate of lead paste alone was used; but even in this case 

 the injury was not severe enough to cause premature defoliation. 

 Plats III and IV, which received 3 pounds and 2 pounds, respectively, 

 of paste arsenate of lead plus 3 pounds of lime to each 50 gallons of 

 water, showed rather serious arsenical injury to the margins of the 

 leaves, while Plats I and II, which received 1^ pounds and 1 pound, 

 respectively, of the powdered form of arsenate of lead plus 3 pounds 

 of lime to 50 gallons of water, showed no appreciable injury to the 

 foliage. From these observations the powdered form of lead arsenate 

 appears less likely to cause injury to the foliage than does the paste 

 form. 



Under no circumstances was it found safe to use effective dosages 

 of lead arsenate (triplumbic or diplumbic) in either the paste or 

 powdered form on pecan foliage without the addition of 3 or 4 pounds 

 of stone lime per 50 gallons of water. The work with arsenicals indi- 



