ARSENATE OF LEAD AGAINST TOBACCO HOENWORMS. 9 



THE GRADE OF ARSENATE OF LEAD TO USE AGAINST THE TOBACCO 



HORNWORMS. 



Arsenates of lead, theoretically, are either triplumbic or diplumbic, 

 although many of the grades and brands are undoubtedly a mixture 

 of the two. Numerous experiments by agents of the bureau have 

 proved that triplumbic arsenate of lead is a very unsatisfactory 

 insecticide for use against tobacco hornworms; in fact the insecti- 

 cidal action of this grade is so slow that very few growers would 

 accept an application as a gift. On the other hand, an arsenate of 

 lead composed almost entirely of the diplumbic form produces very 

 satisfactory insecticidal results when used against this insect. 



In both the triplumbic and diplumbic forms the arsenic is present 

 as arsenic acid. Theoretically triplumbic arsenate of lead in pow- 

 dered form contains 25.58 per cent of arsenic acid, while the diplum- 

 bic, in powdered form, contains theoretically 33.15 per cent of 

 arsenic acid. Tobacco growers should demand a powdered arsenate 

 of lead that is composed largely of the diplumbic fonn. In order to 

 be certain that the diplumbic form is predominant buy only those 

 powdered arsenates of lead which the manufacturers will guarantee 

 to contain at least 30 per cent of arsenic acid; also insist upon a 

 guaranty of not more than 1 per cent of free, or water-soluble, arseni- 

 ous acid, in order to be sure that the applications will not burn the 

 tobacco. The writers advise growers and dealers who may use or 

 handle powdered arsenate of lead for use against tobacco worms to 

 demand a written guaranty that the composition of the products is 

 as recommended above. 



WHEN TO APPLY ARSENATE OF LEAD. 



The first application of arsenate of lead should be made when 

 tobacco worms become too numerous to be kept off tobacco by the 

 hand-picking that is usually done while hoeing, suckering, or topping 

 tobacco. In some years a second and even a third application may 

 be necessary. The time for making these applications will be indi- 

 cated by the numbers of eggs and young worms appearing on the 

 tobacco. 



DOSAGE OF ARSENATE OF LEAD REQUIRED. 



When tobacco is small and has not begim to lap in the row an 

 application of 3^ pounds of arsenate of lead per acre will be efficient. 

 Full-grown tobacco should receive not less than 5 pounds per acre. 

 In water spray use 3 to 4 pounds of powdered arsenate of lead per 

 100 gallons of water. 



