Arsenate of lead as an insecticide against the tobacco hornworms

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Title:
Arsenate of lead as an insecticide against the tobacco hornworms
Series Title:
United States. Dept. of Agriculture. Bureau of Entomology. Circular
Physical Description:
ii, 10 p. : ill. ; 23 cm.
Language:
English
Creator:
Morgan, A. C
Parman, D. C. ( joint author )
Publisher:
Govt. Print. Off.
Place of Publication:
Washington
Publication Date:

Subjects

Subjects / Keywords:
Lead arsenate   ( lcsh )
Genre:
abstract or summary   ( marcgt )
federal government publication   ( marcgt )
non-fiction   ( marcgt )

Notes

Statement of Responsibility:
By A.C. Morgan and D.C. Parman.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 029646868
oclc - 27979939
lccn - agr13000530
Classification:
lcc - SB818 .C6 no.173 1913
System ID:
AA00020832:00001

Full Text
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U. S. PEAARTM.T-NT (I) .\(;RI('I'I.'I'RE.,
BUREAU OF ENTOMOLOGY CIRCULAR No. 173.
L 0 HO.N ARD). [. ninnbl-sl and ( hril Ol R ld.au







TD
ARSENATE OF LEAD AS AN INTs Ir t r 'ilPE

AGAIN-T TIlE :' TOBlACCO liOIRN\OI!MS.




BY

A. C. MORGAN .A%, D. C PARMAN,
Lilomoloqt, uil .iss1t3,.10 .


AA.-Iha T-7% uCLmiMiL'hT PBIhTiM2" OICE i|1






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6647T-13



















BUREAU OF ENTOMOLOGY.


L. 0. HOWARD, Entomologist and Chief of Bureau.
C. L. MARLATT, Entomologist and Acting Chief in Abscnce of Chief.
R. S. CLIFTON, Executive Assistant.
W. F. TASTET, Chief Clerk.

F. H. CHITTENDEN, in chargeof truck crop and stored product insect investigations.
A. D. HOPKINS, in charge of forest insect investigations.
W. D. HUNTER, in charge of southern field crop insect investigations.
F. M. WEBSTER, in charge of cereal and forage insect investigations.
A. L. QUAINTANCE, in charge of deciduous fruit insect inrestigotions.
E. F. PHILLIPS, in charge of bee culture.
D. M. ROGERS, in charge of preventing spread of moths, field work.
ROLLA P. CURRIE, in charge of editorial work.
MABEL COLCORD, in charge of library.

SOUTHERN FIELD CROP INSECT INVESTIGATION.

W. D. HUNTER, in charge.

W. D. PIERCE, J. D. MITCHELL, G. D. SMITH, E. A. MCGREGOR. HA&RY PINKuS.
B. R. COAD, W. A. THOMAS, R. W. MORELAND, A. W. JOBBINS-POMEBOY, C. E.
HESTER, engaged in cotton-boll wceril investigations.
A. C. MORGAN, G. A. RUNNER, S. E. CRUMB, D. C. PARMAN, engaged in tobacco
insect in resligutioni.
F. C. BISHOPP, A. H. JENNINGS, H. P. WOOD, W. V. KING, engaged in tick invcsti-
tions.
T. E. HOLLOWAY, E. R. BARBER, engaged in sugar-lane insect investigations.
J. L. WEBB, engaged in rice insect inreslioations.
R. A. COOLEY, D. LI. VAN DINE, A. F. CONRADI, C. C. KBUMBHAAI, collaborators.
(n)













CIRCULAR NO. 173.


United States Department of Agriculture,

BUREAU OF ENTOMOLOGY.
L. 0. HOWARD, Entomologimt and Chief of Bureau.


ARSENATE OF LEAD AS AN INSE(TICII)DE AGAINST THE
TOBACCO HIORNWORMS.
]By A. C. MOR(;AN ind D. C. PAkRMAN,
Ent,,iiiiligi'al Assistants.

IN' TRODuCr0RY.

During the past five years the Bureau of Entomnlngy has been
conducting an investigation of tobacco ini,.'ts in Tenrn,--,, and
Kentucky and in some of the adjoining St.ite-. In Tennessee the
Iureau has been very materially assisted by Prof. H. A. Morgan,
director of the Tennessee Agricultural Experiment Station.
In the dark-tobacco districts of Kentucky and Tennesseve tobacco
hornworms are the ever-present and most serious problem of the
tobacco grower. Ten to twelve years agn. when labor wa-, plentiful,
cheap, and efficient. "hand-worming" was found to be economical
and effective in combating this pest. However, during the last six or
eight years hand-worming has become too costly, because of the
great scarcity of labor, and too inefficient, and the growers have been
fur'ed to employ an insecticide. At the time insecticide- were fir.t
iised Paris green was found to le the sa fost and most nfficient. Nv-
eriheless. there has always been complaint of frequent serious burn-
ing of tobacco as a result of its use. To find a safe and eftT,,tive
insecticide has been one of the main lines of investigation by the
writers during the past five years. Di-pliimbic arsenate of lead has
been found to meet the requirements. In the further discus-inn of
this iihbject the use and action of Paris green will be rather thor-
oughly discussed in connection with the use and action of arsenate
of lead. for the reason that since the inweticidal results of the use of
Paris green are so well known it will be easier to explain the value
of arsenate of lead if it be compared with this well-known poison.
1


1IJ-lt MurN 1913HI.






2 ARSENATE OF LEAD AGAINST TOBACCO HOBNWORMS.

NECESSITY AND ADVANTAGES OF THE USE OF AN INSECTICIDE.

The way in which the scarcity of labor tended to bring about the
use of an insecticide upon tobacco has already been explained. In
addition to this necessity of using insecticides, the much greater
efficiency of a good application of an insecticide is another strong
argument in its favor. Hand-worming, even of the best, has many
objections; for instance, eggs are not picked off, many small worms
are overlooked on account of their small size, and, lastly, during the
hot hours of the day large worms crawl down into the "ruffles" near
the bases of the leaves and a considerable number are thus over-
looked. On the other hand, a thorough application of an insecti-
cide will kill practically every hornworm-except those very nearly
full grown-within two or three days, and will also continue to kill
the young worms that hatch several days after the application. In
short, hand-picking has only an immediate effect in lessening the
worms, whereas the application of an insecticide usually continues to
kill over a period of several days. Cheapness is another point very
greatly in favor of an insecticide as compared with hand-picking.
The cost of keeping an acre of tobacco hand-wormed in a year when
worms are plentiful is variously estimated at from $6 to $10. A like
number of worms can be killed with an insecticide at a cost of not
more than $2 or $3 an acre-sometimes less.
THE USE OF PARIS GREEN.

In some districts of Kentucky Paris green has been in use for over
a decade. In the dark-tobacco districts of Kentucky and Tennessee
it certainly was used to some extent 10 years ago and at the present
time is in very general use. On account of the frequent injury to
tobacco by the use of this insecticide many farmers would not use it
if labor could be secured to do the hand-picking. On the whole, the
cost of the Paris green plus the cost of application, plus the loss
due to damaged tobacco, is much less than the cost of hand-worming.
In this district the use of insecticides has come to stay. It is a neces-
sity.
Paris green is applied with a dust gun and without a carrier.
From 1 to 2 pounds per acre is the usual application; 1 pound when
worms are small (i. e., less than half grown) and 2 pounds when
there are many worms over half grown. Success with the applica-
tion depends upon the judgment of the farmer in choosing the time
of application and upon the thoroughness with which the application
is made. Much of the tobacco that is injured by Paris green is in-
jured because of unevenness of application, or. what is too frequently
the case. because the grower has delayed the application until half-







SAIt.,"NA'I E ti I I Wi %,t.\l\-] i\-] r t |tti \\M'IIMl a
I r,',ii or two thirds I-I '1 n worms IIv a v becoe m ,,ini l Ir',,v ni-
| liit' l-.I, and has then put on a III rg, and iillltn-v'1 1ijpl 'lic', iitii with thl
thope thi1 he would kill il, thhe 1;ar't worIns. Ti. is an I, ;i ,ipih of
I r ir jiii gTi-i lt. i'*, aIppl i'li,(,11 should have eln made. Ti
tirs't .,hid lhave been smaller and at an earlier date in n'ild. to kill
lite worms while nial. inil also to lessen the -ni4l',r ,f 1rlill (i the
tlu i',111. lTh, second ;al)Ilii>l'ii, ,i, would I'lli, as soon011 as wormi
begin to increase inii i1iifivC. aflcr the tirvt application.
OBJFtI. 'iuI TO il USE OF PARIS 1,I-.l.N.
DANGER. TO THE OPVERATOlB.
Then' is occasionally someI iiji,,, or irritation to the ,peralor in
applying Paris grt'en. Wl\re.cr Paris gretVii strikes the tender
part-, of the body irritation soon occurs unless a tlihii-u'igh bath be
taken proinptly. Ihli iud at the nose sometimes occurs as a result of
the irritation to the mucous iiuiiijr0ient-. For these reasons many
peolile dislike to ailply Paris gri,. llowever, if care is taken to
work in a direction yill rteri ,.. the breeze and upon the windward
-idle of the row while iiiiLinjg an p11 p li,.itti',,. a thick sack around
the bodly and a "pug' over the nose will be found to be eXt- lleuit
preventive of irritatlioii. particularly if followed by a bath.
INJUTRY Y PABIS UKREU TO TOBACCO.
The Nery general complaint of loss due to Pi..r,.xTI-liIr-ued to-
bacco has been fotndI to be j11,ttied. I'h.d-Ir fav!iorable weather con-
ditions 2 poul- iif Paris gteii per arre, sometimes iin,. may be
applied without noticeable injury. On the other ia:d.111 unfavorable
weaither conditions will frequently cause injury to fo11ow an appli-
tation of only 1 pound wper acre. Vr'y hot suns and low humidity
for an extended period \ ill produce a condition of the tobacco pl.iit
Icry V iV-n piihli to la.ri--green burn. Light rains or %try heavy
dews immedictkelv fi11h,\ in,, an application will wash the Paris grer..
down into tlie axils (f the leaves or into the fuirrow- alnig the mid-
ih-. and serious injury is likely to result.
In tihe ('ltrk-' ill, district of the lairk-tobacco belt of Kentucky
01nd Tennessee Pari-- gren burn was quite severe dluriung 1911 and
1'.1l2. particularly so in 1912. Previou-s to these y.ar, one of the
most careful gro'er- in this district informed the writers that his
I-, on a 6-acre fieldI of tobau'Co. due to Pari-,_reen btlri. amounted
Iii 8 per cent g'ro,-. which was a loss of at least 16 per cent of the net
profit, and that many other growers suffered a similar loss in 191-2.
In 1911 the writers observed many field in which the ls equaled
or exceeded that quoted above. In 1912. however, the injury by Paris
green was more widespread than for ev\r.al years, notwitli-t.undiiiirg




id






4 ARSF.NATE OF LEAD AGAINST TOBACCO HORNWORMS.

the fact that many growers who suffered loss the year before were
extremely careful in making applications.
On January 4, 1913, the senior writer interviewed several tobacco
buyers employed by the Italian Government. He was informed that
several crops of tobacco the grade of which was especially suitable
for the Italian Government were not bid upon because of the large
percentage of tobacco injured by Paris green. The buyer stated that
for one crop, had it been in average condition in regard to Paris-
green injury, he would have bid 8J cents per pound. In its damaged
condition, however, he did not believe the crop was worth over 5.
cents per pound-a gross loss of 31 cents per pound, or of $25 to $30
per acre. Another crop would have received an offer of 8 cents per
pound from the Italian buyers, but on account of Paris-green burn no
offer was made. This buyer thought the crop worth not more than
5 cents-a gross loss of 21 cents per pound, or about $20 per acre.
A third crop had its value reduced by one-half, a fourth crop was
apparently worth about 5 cents per pound, and would ordinarily have
brought 9 cents. This is the report of buyers of the heavier types of
tobacco grown in this district. The lighter-bodied tobaccos undoubt-
edly suffered as severely and probably more severely than the heavier
tobaccos, because the lighter tobaccos are ordinarily more susceptible
to Paris-green injury.
Paris green injures tobacco in two ways: First, by causing dead,
burned areas upon the leaves, where the powder has been collected by
the dews or washed down by the rains;, second, by weakening the leaf
at the stalk. Light rains wash the insecticide into the axils of the
leaves, and the result is that many leaves drop off before cutting time
or become so weakened that they drop off when the plant is cut.
Such leaves are not a total loss, for they are collected and cured, but
they are a partial loss. They are light in weight and lack gloss and
elasticity.
THE USE OF ARSENATE OF LEAD.
Arsenate of lead causes none of the injury mentioned above. Ex-
periments performed under the direction of the senior writer showed
that powdered arsenate of lead may be put on a fresh sucker wound
in large quantities without causing any noticeable injury, and that
when applied to a torn or bruised leaf it produces no injury. Paris
green can not be applied to tobacco in the "graining" stage (i. e..
when nearly ripe) in sufficient quantities to do good insecticidal work
without too grave danger of burning the plant. Arsenate of lead. on
the other hand, can be safely applied to tobacco in the "graining"
stage in quantities sufficient to produce satisfactory insecticidal re-
sults. Furthermore, arsenate of lead will cause no irritation to the







ARSENATI. UFi. LEADl AUAlNbi ll lt Lii ti1lINW M..

opernt)r as will I'ari. grerii; in fat, thus fliar it has ii.' lirI no
noticel Iilt. injurioulls t'tl' s u pol) the o elrniatiors.
iWilnc ;irm-nite of lead van be applied to tobacco without injuring.,
the plant, and since it is 'rv 1iiinh less olije'rtiiin,,lh from the oper-
ator's standpoint, its insecticidal properties should next be disc.smJd.
As the do.sige and arctlin of Paris irreeii are very idel kI,,II the
value of arsenate of lead as an insecticide can the more easiIly be
explained by (,iparin-g it wVithI Paris giri, The followNilg table
will ser e to show the relative values of the two irnsrticihles under
different couiindiltion.s.
TABLE I.- Ciipirivfi ,,f thr in-'., ti, adul ,'r t, 1, ,i 1 inl hotwnmormsa iof arseatfe
of lead and 4 'ur.i, y i n in fair wt .ftir'r.

S1" m.,im unliL a .. %,u M l.u I tII t-' r uf .r lril I- k i
Oi fii' Ihh
O n day On IIL ond third 1 rt fit


9 i- ------ --- -- -
;IP Date.- of uav tS1^ d (W f' h firth 7




.,,g .5 ooIO 5 ,..,,I.'d ,na .'I4 Ot,6S, i :2 "..,2
__ _ _ __ _ _ It _ p____ I_ _
rn ol I Ien N. 1 an w al u
iU f or conditions ise, plter a d upon t ,laN and



favorable~~ ~ fi codtos Trs he eiwt kile wr s vet-r,
I AUg *NS 1010 5 .> Lefad iuwnen W 1I34 1 0 I 46 |W 24 -;I .i '; '"
2 s .. ,o .I. Th IJO r 71c in I .l I w iu 1* .I '. th
3 AI "14 lg91l 1) V'tri, 'rv i. 'll"J 0 J."i i 4 i ", 1 -' :,, '"1
4 Alc t :1 lN.ll 41 .l r-puntte l.1 5 j. f a r :r s -n t', ] .1 .V. g e t'
b Aus g 2:.lll : 1o'n Patm grefn.. 'i 7 m 17 1 Itf :n i 1a 3 p.t o 2 live
r Twern fD -TO pluaiun di nd urinary hild-worming.
*Mwi% U mall sorms hlive

Arsenate-of-lead experiments Nos. 1 and 2 were applied under
very favorable conditions, i. e., there was dew upon the plants and
no breeze. Paris-green application No. 3 was applied under equally
favorable conditions. These three experiments killed worms very
satisfactorily. The records in Table I were maic I,-\ coutiilng the
worms on .50 plants of tobacco on each succee.,ling ,1.i, after the ap-
plication. No. 1, 5-pound dosage of arsenate of le;ha1, gave the
best re.-tilts. for on the fourth d;,\ afirr the application only 2 live
worms were fnitnd in hand-norminir 20) hills. The :_i-pwIind dosage
of arsenate of lead was not quite so good. alt]ho,11,0 only 14 live worms
were found on *2<0 plants the fourth diaty after the application. The
Paris-green application No. 3 killed more quickly than either of the
applications of senate of lead, but on the fifth day after the appli-
cation numerous small worms were noticed in woring 200 plants.
It was thus apparent that the Paris green was lo-ingu its ruf'ect. owing
to heavy dews which tended to puddle it. and to heavy drx ing wind.
during the day, which blew some of it from the plants.
The application in experiment No. 4 was not made under the most
favorable conditions. There was a slight breeze during the appli-







6 ARSENATE OF LEAD AGAINST TOBACCO HORNWOBMS.

cation; in addition, there were a large number of eggs on the plants,
and many of the young worms hatching from these eggs were not
killed until they wandered from the place of hatching. The same
is true of experiment No. 5, the 1l-pound dosage of Paris green. It
will be seen, however, that experiment No. 4, the arsenate-of-lead
application, was more effective than the Paris-green application, for
on the day of application there were at least 140 worms in experi-
ment No. 4, the arsenate-of-lead application, and only 114 worms in
experiment No. 5, the Paris-green application, while on the fourth
day after the applications there were only 31 live worms in experi-
minent No. 4, but 52 in experiment No. 5.
The poisons were applied in the following series of tests in the
morning from 6.30 to 9 o'clock. The arsenate of lead was mixed with
an equal weight of dry wood ashes. All applications were made with
fan dust guns. The mixture of ashes and lead arsenate made a very
good dust and compared favorably in evenness with the application
of Paris green. Rain began to fall at 11.30 a. m. and continued in-
termittently until 2 p.m. Part of the rain was dashing. About one-
third of an inch fell. The first examination of thle plats was made
after 3 p. m. of the same day. The tobacco on these plats was nearly
full grown and lapped in the rows considerably.

TABLE II.-A comparison of the, insecticidal (ffect.s against horn-worms of
arsenate of lead and Puris green in rainy weather.

Examinations to show number of worms
killed.
eAOndy Onnfist On On On
z Date of Dosage Poison used. On day i second third four Size at
application. applied. dav day 'lay worms left.
0 after, after. after.
Q 4
c-: *!' ~i.. .1.i^ ..I.g

Pund,
ptriun
I Aug! 2 1911 5 Lead arsenae. 59 49 15 41 10 I 2 Small.
2 .. do ... 4 .do ...... 102 21 4 27 21 13 .. 33 8 Small and
I medium.
3 ... o d . 2, Parsg repn.... 13 .54 341 14 36 9 Sm all to
large.

The three experiments recorded in Table II are very interesting.
They show, first, that arsenate of lead was far more effective during
rainy weather than was Paris green (see number of live worms on
the fourth day), even though a very heavy dosage of Paris green
was used; second, that to be very effective during rainy weather an
application of at least 5 pounds of arsenate of lead per acre is re-








quired. KIprriinent No. 2. 4 iiiil- of arentate (f lead per acreo.
was more elff,'rtim I11i:i Ihe 2.'1 pounds of Punri, fr,,,.. .liii.li,.. a
tsidti'ra1fh number 'if worms were I.fi on plat ".'. we tind that f,,,ri
wHee livre in this experiment on the f., 'iii li vy than ",,r. alive in
the im, rIk grlIn exlriniimnt. nii, i h~-I ,ding the fart that there wen,
pnicrticalvly 2(i per cent more woriwms on No. _'. the airsenate ,f lead
111111. at the time Elf a ,liu lliol, iif the poison than there were on tIhe
r'ii gi-reen plat. I'ortunately for the itl I upon thle t4dobacco 13.t-.
the rain witl1.ii1 1,tI nearly ,ll the Paris L_,,.i. 1so that there w-' very
li tle burininig. lThere %was )no liiuriiig of planti- onII the ar-euate ,If
Ifall plants.
TAB F I II.-Comptuy ison ul tn tI'ididal vf,, 1t ,,f 11,',i, a,! fnd ,,""r /ippHflI tn' of
IrfV1 ttltt, of hItdi.


F1,,d .lr.r1| 1111U I hj .lll ll Il. u, Hurilli
Df Pale of 3ii.4.li D Ft vond 'Thi sourtl

I I W \ -
-. 1 - 2




pli .atin of arl na) t4 of lead, 1 lica 41 ti No. 1, 4 ,- -ar senr, arflnte


(f lead per acre. was from the same keg as application 2,. _1,
2 Pounds per acre. ioits were ti3 O h15 31 [i.. in AIhn nr, ilntace.


Oin Augu,{ It6. 1910.ql0, niar, v were no,{ced on the lnt-, so that
mInst of the worms amaring on thmparison plat were ,nmll. It a p11 b
p~licationI of arsenate of lead, application No. 1, -1, peiiu ii i. arsenate
of lead per acre, was froni the sanme lieg as application No. *-' 8'*
pounds per arei. 1'ouits were TIIiiId on 5"i hillk in each instance.
On Augii~I Itl. 1H10O. niirn ev were nolicedl on the jibtif-, so that
motof liht worms appearing on this plat were ..rn~ull. It will lbe
noticed that the application did not keep domn the increase (if worms
due to hatching. In experiment No. 2 there were very few ,ii2,g- on
the plants and the worms were therefore lar,_er than on plat 1 1anl
harder to kill. 'Pructirally a clean -vt'ip was made on N,1. *2. only
14 worms heinir found on 200 plants on the fourth ildiy after the
aplpliration. Fa\oralble weather pri-vailed after both anjilintiin.
and the conditions at the time of appli'ti itn to both plats were
equally favorable. WhaLt. then, is the explidinitlimn of the poor results
on plat 1 and of the very excellent results on plat 2t T"i' ecxpli an:-
tion is found in the carrier. In No. 1 the arsenate of l1.id was mixed
thoroughly with an equal weight of ituely sIftled air-slaked liiii,.
while in No. 2 it was thoroughly mixed with an equal weight ,f
finely sifted dry wood ashes. Nuwithitanidiiig the dri.-.. of the




A


ARSK.NATK .11' I 'I \I ",1 li'll i n l111 H! \' "i M .






ARSF.NAI1E OF LEAD AGAINST TOBACCO HORNWOBMS.


lime the mixture lumped out of the gun considerably. On the other
hand, the arsenate of lead and ashes made a very even dust, with
scarcely any lumping. These two experiments are here shown to
emphasize the necessity of applying a thoroughly even dust. A
lumpy application is a waste of time and material and will be no
more effective than would a perfect application which had been
rained upon immediately following the application.

HOW TO APPLY ARSENATE OF LEAD TO TOBACCO.

Paris green is generally applied to tobacco by means of a dust
gun and without the admixture of a carrier. On the other hand,
arsenate of lead must be mixed with a carrier in order to secure an
even and thorough distribution. Several carriers have been tested
with this insecticide. Finely sifted air-slaked lime, to our surprise,
did not dust evenly. Road dust and land plaster proved to be too
heavy. The best results were obtained with finely sifted, freshly burned
wood ashes. At least an equal bulk of the wood ashes should be used.
Mix the arsenate of lead and ashes very thoroughly and apply while
there is dew upon the tobacco and when there is no breeze. Even if
very dry and finely sifted ashes are used, unsatisfactory results will
be obtained unless the application is made with a powerful dust gun.
The hand-power dust guns now in general use do not furnish suffi-
cient power to make anything like a satisfactory and effective appli-
cation. Special guns that will perform satisfactory work are gradu-
ally coming on the market. The new guns have a fan with a diame-
ter of 8 inches, whereas the old guns have a fan diameter of only 6
inches. The new guns have also an auxiliary dust chamber, which
is very essential, because the dust containers of the old guns are so
small that they have to be refilled five or six times for each acre
dusted. Two refillings of the new guns will be sufficient for dusting
an acre.
To secure the best results dust the tobacco when dew is upon the
plants and when there is no breeze. By reference to Table III we
see the comparative results of a good and a poor application of
trsenate of lead. The use of a carrier that does not dust evenly, the
application of the insecticide when there is too much breeze, and the
use of too small a dust gun are all certain to give unsatisfactory
results. Avoid these mistakes, and satisfactory results will be secured.
Thoroughness of application can not be too strongly recommended.
When tobacco worms are numerous a poor application of an insecti-
cide will miss worms enough to ruin in two days more than enough
tobacco to pay for the whole application. Make the application
thorough.




1

ARK.'N \'l-. iQ." LEAD t. ilN.SI lIt 'll\(.l'l Iu NWuII M.' 9

THE GRADE OF ARSENATE OF vTO U AGAINST THE P)BACCO
l1 41 NM\I t(M'' 4.

Arsena(es of lead. theoretically, are either triplumbic or ,lip lumibi,.
although many of the grilialc. and brands are iundoubteCdly a mixture
of the two. Nunivrrus experiments by igit, of the bureau have
proved that tripliiinbic arsenate 4f lead is a very iin. .ti-f.'Ctiry
insecticide for use against tobacco horiworms; in fact the insecti-
cidal action of this graie is so slow that \vry few gr-icrs would
accept an applications as a gift. On the other aU,1l. an arsenate of
lead composed almost entirely of the diplumbic form produces vrv
satisfactory in.M'cti.idail results when used ia irist this insect.
In both the tripliunbic and diplumbic forms the arsenic is present
as arsenic acid. Theoiretlicvill triplumbic ;irsenale of lh-:id in pow-
dered form contains 25..',, per cent of arsenic acid, while the dlipllii,-
bic, in powdered forIm, contains theoretically 33:.1.', per cent of
arsenic acid. Tolmacco growers sliul euiiin riand a p))wdr'Vd arsenate
of lead that is composed largely v of the ilipliirnbic funny. In order to
be certain that the dipliiibic form is prvioiii il,,.lnt linuy only those
powdered arv'niites of lead which the manufacturers wiIll 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.-u1Lble, arseni-
ous acid, in order to be sure that the applications will not burn the
tobacco. The vriters advise grrers aid dealers who may use or
handle powdered arsenate of lead for use aginit tolpacro worms to
demand a written guairinty 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 niiumerous to be kept ,ff tobacco by lthe
hand-picking that is usually done while hoeing, uir,'kvring, or topping
tobacco. In some Years a second and even a third application may
be necessary. The time for niaking the-.e appli'caitions %%ill be indi-
cated by the numbers of e.-,. and youiir worms a;ppeiariig on the
tobacco.
DOSAGE OF ARSENATE OF LEAD REQlIREI).

When tobacco is small and has not begiin to lap in the row an
application of .' 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.







ARSENATE OF LEAD AGAINST'r TOBACCO HORNWORMS.


COST OF ARSNATE OF LEAD.
The special grade of powdered arsenate of lead recommended for
use on tobacco will cost about 22 cents per pound at the factory in
100-pound kegs. The freight will be about 1 cent per pound, mak-
ing the total cost 23 cents per pound to the grower. Therefore a 3.-
pound dou-,ige will cost about 80 cents, while a 5-pound dosage will
cost $1.15. A 2-pound ilu-:ige of Paris green costs from 50 to 55
cents, while a dosage of 1- poiund-, which is the smallest which should
be applied, will cost about 31 to 35 cents. If the comiiparative co-,t
of Paris green and arsenate of lead were the only quest ion to be con-
sidered, it would be useless to recommend arsenate of lead. The
cost, however, for the careful grower should be a matter of strictly
secondary consideration. The certainty of not burning the tobacco
should more than compensate for the extra cost of this insecticide.
SUMMARY.
Paris green frequently burns tobacco v-ery severely, and may
reduce the value of the crop as much as 5( per cent in exceptional
cases.
It is impossible to apply an effective d,,;ige of Paris green without
risk of burning tobacco.
Paris green, which is applied in dust form, is used at a dosage of
from 1 to 2 pounds per acre.
Arsenate of lead is safe and effective during rainy weather, while
Paris green is dangerous and ineffective.
It is recommended that arsenate of lead be used against the tobacco
hornworms, and that it be applied as a dust or powder.
The dosage of arsenate of lead in powdered form varies from 3A
pounds per acre to 5 pounds per acre. If applied as a spray, use 3
to 4 pounds in 100 gallons of water.
Arsenate of lead applied in powdered form. as here recommended,
must be mixed with a carrier. The best carrier found so far is dry
wood ashes, used in a bulk at least equal to the arsenate of lead.
In applying arsenate of lead u..e a dust gun having a fan diameter
of at least 8 inches.
Apply arsenate of lead when there is no breeze and when dew is
on the plants.
Approved:
JAMES WII.',iN.
Secretary of Agriultfire.
WASHINGTON, D. C., Ft l1,i,'!/ 6. 1913.

ADDITIONAL COPIES of this publication
may be procured from the SUPERNTENIrD-
INT OF DOCtrMEN'S, Government Printing
Office, Washington, D. C.. at 5 cenLts per copy







UNIVERSITY OF FLORIDA
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