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UNITED STATES DEPARTMENT OF AGRICULTURE

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WASHINGTON, D. C. PROFESSIONAL PAPER April 5, 1923

THE INFLUENCE OF COPPER SPRAYS ON. THE
an oy COMPOSITION OF IRISH POTATO
ERS.

By F. ©. Coox, Physiological Chemist, Insecticide and Fungicide Laboratory,
Miscellaneous Division, Bureau of Chemistry.

CONTENTS.
Page. Page.
Purpose of investigation__________ 1 | Results of experimental work—Con.
Results of previous investigations: Influence of strength and num-
weieldoor potatoes. =. 2 aos ee 2 ber of applications of copper
Composition of potatoes ______ 3 sprays on composition of
Pl antse ce SeCNeT Al 2 4 tubers #2. 2 eee eee 17
Experimental procedure___________ 7 | Influence of environment on com-
Results of experimental work : MOSsition Of. tupeESs | — eee 18
Changes in composition of tubers Copper content of vines, stems,.
Gunns! -STOw theese SE es bs tl roots, and tubers of sprayed
Effect of copper sprays on yield and unsprayed plants ______ 19
and composition of tubers___ 10 |" General ‘discussion == aaa 21
Proportion of tubers to vines Summ anya 5 te ee ee 23
DLS. GUDeCISS sos eke ee Gel iteracure’ Cited. = oe a eee 24

PURPOSE OF INVESTIGATION.

For years Bordeaux sprays have been applied to the potato plant
to control fungous diseases, particularly in the northern parts of the
country where the late blight (Phytophthora infestans) frequently
causes serious losses. In those parts of the Central and Southern
States where potatoes are grown the only spray ordinarily applied
igs an arsenical to control the Colorado potato beetle. Arsenicals are
‘usually added to the Bordeaux sprays. The formule of Bordeaux
sprays may vary in different localities. A 5-5-50 spray is one in
which 5 pounds of copper sulphate and 5 pounds of lime are used
and the spray is made to 50 gallons with water.

The fact that potato plants treated with Bordeaux spray give
larger yields of tubers than those which do not receive such applica-
tions‘ has been established by a series of experiments extending over
many years at the Vermont, Maine, and New York agricultural ex-
periment stations. The influence of the copper sprays on the com-
position of the tubers, however, has received no detailed study in this
country. In view of the importance of the potato crop it is surpris-
ing that practically no detailed analyses of potato tubers grown in
the United States are available.

meager pa se oy

2, BULLETIN 1146, U. S. DEPARTMENT OF AGRICULTURE.

When in 1917 it was found that the solids, starch, and nitrogen
contents of tubers from copper-sprayed potato plants were greater
than those of tubers from unsprayed plants, an investigation was
begun in the Bureau of Chemistry to determine the effect of Picker-
ing sprays, barium-water sprays, and standard Bordeaux sprays as
compared with that of noncopper sprays on the yield and on the com-
position of potatoes grown in different localities. The distribution
of copper in the tubers, roots, stems, and leaves of the various
sprayed and unsprayed potato plants was studied also.

RESULTS OF PREVIOUS INVESTIGATIONS.

YIELD OF POTATOES.

Giddings (20),’ of the West Virginia station, fund that in 1909
three applications of Bordeaux increased the yield of potatoes 53.5
per cent and that in 1910 four applications increased the yield 39.3

er cent.

E In New York Stewart and his associates (46, 47,45) have conducted
an extensive series of experiments to show the Benen: of Bordeaux
spraying. In discussing the results obtained at the New York station
in 1911 Stewart stated: ‘“ There was no late blight whatever, only a
very little early blight and very little flea-beetle injury. The un-
sprayed rows were affected by no disease of any consequence except

tip burn and even of that there was only a moderateamount, * * *-
yet spraying increased the yield at the rate of 98 bushels per acre.
Plainly we have here a striking example of the beneficial influence of
Bordeaux in the absence of disease and insect enemies.’

In 1912 Lutman (32) published data from Vermont showing that
a greater yield of tubers was obtained from copper-sprayed potato
plants at various stages of growth than from the unsprayed plants.
Plants which received a Pickering spray, a Bordeaux spray in which |
part of the copper sulphate had been replaced by iron sulphate, and
a commercial spray containing copper also gave higher yields than
the check plants. The increased yield seemed to be in proportion to
the amount of copper present in the spray. The application of a
spray containing silver did not increase the yield. Lutman sug-
gested that the Bordeaux mixture acts asa stimulant, bringing about
an increase in the quantity of starch produced daily.

Clinton (8) in 1915 reported that homemade Bordeaux sprays used
on potatoes in Connecticut uniformly increased the yields. Thé
average increase for the sprayed plants during the 13 years that the
tests were carried on was 36 bushels an acre. -

In 1916 Lutman (33) reported the results he obtained in 1912 from
using 5-5-50 Bordeaux and 24-24-50 Bordeaux on potatoes in Ver-
‘mont. He concluded that “the amount of copper sulphate and lime
used did not appear to be important providing the mixture was fairly
strong. A little difference appeared in favor of the 5-550 combina-
tion over the 24-24-50. Frequent and early sprayings did not seem
favorably to affect the yield of tubers. Some of the plants were
sprayed ten times but they produced little or no larger crops than
did those plants sprayed less often.” .He stated further that the use

* Italic figures in parentheses refer to literature cited at end of bulletin.

COPPER SPRAYS ON IRISH POTATO TUBERS. 3

of Bordeaux under field conditions increases the yield of tubers from
potato plants by preventing tip burn and flea-beetle injury. He be-
lieved that the yields are not increased when plants which are not
troubled by tip burn or flea beetle are sprayed. According to this
investigator, Bordeaux mixture seems in the long run to be neither
beneficial nor harmful, but it is unnecessary to apply it to plants
grown in the greenhouse or to those in regions where neither tip
burn nor flea beetles are a factor in potato growing and where neither
early nor late blight occurs.

Babcock (4) reported in 1917 that spraying potatoes thoroughly
with a 44-50 Bordeaux mixture in Ohio when the plants were about
8 inches high and every 10 days to two weeks thereafter materially
increased the yield, even in years when there were no disease epi-
demics.

Erwin (/6) reported a difference in yield in favor of the Bor-
deaux-sprayed plots, indicating a definite response to the use of
Bordeaux spray in Iowa. . When tip burn was generally present and
early blight practically absent the yields were higher on the sprayed
plots, indicating that the plants had been stimulated and benefited
by the Bordeaux application.

In 1919 Leiby (29) published data obtained in North Carolina
showing an average gain of 51.6 bushels an acre, representing 64.2
per cent, as a result of the use of a 34-50 Bordeaux plus lead
arsenate spray on potatoes. Bordeaux alone produced an increased
yaeld of 35 bushels an acre.

During a 10-year period in New York an average gain of 60
bushels an acre was obtained by spraying with Bordeaux. At the
Vermont station during 20 years, which covered all seasonal varia-
tions, an average gain of 105 bushels of potatoes an acre was effected
by the use of Bordeaux. Experiments at the Maine station extend-
ing over a period of years showed that spraying with Bordeaux gave
increased yields of tubers, even in years when no late blight was
prevalent.

COMPOSITION OF POTATOES.

Although no detailed analyses of potatoes grown in the United
States are available, the results of several analytical studies of
European varieties have been reported.

Kreusler (26) gives the results of analyses of large, medium, and
small tubers grown in Germany. They had the same general com-
position, the only difference being the presence of slightly more crude
fiber and solids in the small than in the large tubers. The medium-
sized tubers had more crude fiber than the large tubers but the same
proportion of solids.

Appleman (2), who investigated the changes in Irish potatoes
_ during storage, gives data on the moisture, total sugar, and starch
contents.

Girard (272) in 1889 reported the changes taking place in tubers in
France during growth. The sucrose content dropped from 1.48 to
0.02. per cent and the dextrose content from 0.67 per cent to none.
Protein increased from 1.36 to 1.98 per cent, ash from 0.86 to 1.46
per cent, starch from 8.4 to 16.38 per cent, and cellulose from 0.84
to 1.66 per cent. The insoluble nitrogen dropped from 1.66 to 0.19
per cent and the insoluble ash from 0.16 to 0.06 per cent.

4 BULLETIN 1146, U. S. DEPARTMENT OF AGRICULTURE.

Pott (37) showed that the water content decreased, while the
total nitrogen, starch, and crude fiber contents increased in the tubers
as they matured. :

Prunet (39) considered that during growth the nutritive sub-
stances are uniformly distributed in the tuber, but after full size has
been reached there is a movement of these substances toward the
apical buds.

Jones and White (24) in 1899 reported some experiments made on
Delaware and White Star varieties of potatoes in Vermont. From
analyses of tubers from both Bordeaux-sprayed and unsprayed plots,
they concluded that the variations in yield were of more importance
than variations in composition. The unsprayed tubers showed the
presence of more water and ash than the sprayed tubers. As all of
the tubers matured the solids and nitrogen-free extract decreased
somewhat, while the ash, protein, and crude fiber increased slightly.

Stewart, Eustace, and Sirrine (46) im 1902 reported that one lot
of tubers from Bordeaux-sprayed plants gave higher solids and
starch results than a corresponding lot from unsprayed vines.

Woods (51) of the Maine station in 1919 published analyses show-
ing that tubers from Bordeaux-sprayed potato vines averaged 19.1
per cent starch and that:tubers in the same field from unsprayed vines
averaged 17.5 per cent starch. The dry matter in the tubers from the
sprayed portions of the field was also 14 per cent higher than that
in the tubers from the unsprayed portions.

PLANTS IN GENERAL.

Sorauer (45) observed that swellings were formed on the leaves of
potato plants by the action of copper salts. Sections of these
growths showed that they were composed of parenchyma cells so
strongly hypertrophied as to break the epidermis.

Frank and Kriiger (79) in 1894 obtained a definite improvement in
growth by treating potato plants with a 2 per cent Bordeaux spray.
The effect of the copper was most marked on the leaves and was
chiefly indicated by physiological activity rather than morphological
changes. The leaves were thicker and stronger and their hfe was
lengthened. The chlorophyll content was apparently increased and
correlated with this was a rise in the assimilating capacity, more
starch being formed. A rise in transpiration also occurred. <A sub-
sidiary stimulation took place in the tubers, as the greater quantity
of starch produced required space for its storage. The ratio of tuber
formation on treated and untreated plants was 19:17 and 17:16.
These investigators held that the action was catalytic, that is, an
increase in photosynthesis resulted from the presence of copper.

Rumm (40) in 1895 noted that grape foliage sprayed with Bor-
deaux showed thickened leaves of a blue-green color which outlived
the leaves of the unsprayed vines. After measuring leaves from
sprayed and unsprayed vines Rumm presented data showing that the
thickness of the leaf, the epidermis, the palisade tissue, and the
parenchyma was increased in the case of the sprayed vines. These
data suggest that copper was taken into the growing leaf where it
produced certain morphological changes.

Lodeman (32) found that the thickness of plum leaves and prune
leaves was increased by the application of Bordeaux spray.

COPPER SPRAYS ON IRISH POTATO TUBERS. 5

Working with a large number of greenhouse plants, Zucker (52)
concluded that plants sprayed with Bordeaux have greater resistance
to etiolation than the unsprayed plants. The sprayed plants also
showed an increase of chlorophyll and an increased power of assimi-
lation, and their shoots lived longer. All of the sprayed plants
transpired more than the unsprayed plants or those sprayed with
lime alone.

Harrison (22) found that Bordeaux-sprayed plum, peach, and pear
leaves were slightly thickened and that a marked development of
chlorophyll granules occurred in their cells.

According to Chuard and Porchet (6), copper spray causes a
slight increase in the sugar content of matured fruits. Injection of
solutions of copper salts into the tissues of such plants as the grape-
vine produced more vigorous growth, more intense color, and greater
persistence of the leaves. ‘The copper seemed to act as a stimulant to
all the cells of the organism. Other metals, such as cadmium and
iron, are said to give a similar effect. Injecting small quantities of
copper salts into the branches of a currant bush caused an acceler-
ation in the maturation of the fruit identical with that obtained by
the application of Bordeaux to the leaves. If the quantity of copper
introduced into the vegetable organism was increased, the toxic action
of the metal was brought into play. These investigators attribute
the stimulus, as shown by the earlier maturation of the fruit, to a
greater activity of all the cells of the organism and not to an excita-
tion of the chlorophyll functions alone.

Treboux (49), in 1903, demonstrated the harmful effect of solu-
tions of copper salts on leaves, measuring the activity of photosyn-
thesis by a determination of the rate of emission of bubbles of oxygen.

Kanda (25) undertook to ascertain whether copper had a stimu-
lating action on plants. He found that very small amounts of copper
sulphate were toxic to peas grown in distilled water.

Schander (4/7) believes that the copper in a Bordeaux spray pene-
trates the leaf to a very small extent, perhaps less than one in a
hundred million parts, and that the copper there produces changes
in assimilation and in transpiration. He considers that the shading
effect of the Bordeaux spray on the leaves is beneficial to the absorp-
tion of carbon dioxid.

Ewert (/7) states that in the morning Bordeaux-sprayed potato
plants contain more starch than the unsprayed plants, not because
‘they are making more starch, but because they are unable to get rid
of it as rapidly. The starch is piled-up in the chlorophyll bodies
as the minute amount of copper absorbed checks the diastase action.
Bordeaux spraying, shading the plants with cloth, and a combination
_ of the two procedures diminish the yield of tubers. This author
demonstrated by its effect on diastase that copper is present in the
sprayed leaf in minute amount and concludes that the organic life
of the plant is hindered rather than stimulated by the application
of Bordeaux sprays.

Von Schrenk (50), working with cauliflower, also observed that
See were formed on the leaves owing to the action of copper
salts.

Amos (1) studied the effect of Bordeaux mixture on the assimila-
tion of carbon dioxid by the leaves of plants to determine whether any

6 BULLETIN 1146, U. S. DEPARTMENT OF AGRICULTURE.

stimulation resulted. He found a diminished assimilation by the
sprayed leaves for a time. This effect, however, gradually disap-
peared. It is suggested that the stomata are blocked by the Bordeaux’
mixture, so that less air is diffused into the intercellular spaces and
less carbon dioxid comes into contact with the absorption surfaces.
This then is a mechanical and not a physiological action that reduces
assimilation.

Duggar and Cooley (74) showed that potted potato plants when
sprayed with Bordeaux transpire more water than unsprayed plants.

Duggar and Cooley (14), using potted potato plants, studied the
effects of surface films on the rate of transpiration. The use of Bor-
deaux and other films increased the rate of transpiration. The plants
treated with weak Bordeaux (2-3-50) were in good condition at
the close of the test, while those sprayed with stronger Bordeaux
(4-6-50) showed injury from too much transpiration. These in-
vestigators stated that it does not follow that the same results will be
obtained in the open.

After measuring the cells of Bordeaux-sprayed and unsprayed
potato leaves, Lutman (33) concluded that in general the leaves
from the Bordeaux-sprayed plants had thicker palisade and pulp
parenchymas than those from the check plants. He believed also that
the number of chlorophyll bodies was increased in the sprayed leaves.
An increased turgor is probably the immediate cause of these un-
_ usually large cells. He considered that a small quantity of copper
enters the leaf and that a chemical combination takes place between
the chlorophyll and the copper. The chlorophyll is less easily re-
moved from sprayed plants, showing that it has been rendered less
soluble. Greenhouse tests and experiments conducted for one year
in Germany by Lutman showed no stimulation effects. Lutman con-
siders that in this country the physiological effects of Bordeaux on
the potato are quite as important as its fungicidal effects. The
physiological effect observed in Vermont is ascribed to lessened tip
burn and flea-beetle injury and not to a stimulation and daily
increase of starch formation as suggested earlier by him.

Edgerton (7/5) decided that Bordeaux apphed in Louisiana de-
layed the ripening of tomatoes, while any increase in yield was un-
certain. Pritchard and Clark (38) concluded that treatment with
copper sprays increased the yield-of tomatoes in Virginia, Mary-
land, Indiana, and New Jersey.

In some of Montemartini’s experiments (36) one side of a plant
was sprayed while the other was not. Leaves sprayed in the morn-
ing with dilute copper sulphate solution and removed and measured
in the evening had a greater dry weight per unit area than the
untreated leaves. When leaves were treated at night and removed
in the morning they had a lower dry weight per unit area than the
untreated leaves. According to Montemartini, these results indi-
cate that the treatment stimulated the formation and translocation
of organic matter. |

Ball (5) has definitely established the fact that the potato leaf-
hopper causes “burning” of potato leaves, to which the term “hop-
perburn” has been applied. He states also that it has long been
recognized that spraying with Bordeaux mixture reduces tip burn,
probably because it acts as a partial repellent against the leafhoppers.

COPPER SPRAYS ON IRISH POTATO TUBERS. 7

Dudley and Wilson (73) report that the potato leafhopper is one
of the most important enemies of the potato in the United States.
Bordeaux repels the leafhopper and therefore effectively controls
the potato leafhopper and hopperburn. According to Fenton and
Hartzell (78), the leafhopper can be effectively controlled and hop-
perburn can be prevented by covering the potato plants with Bor-
deaux spray. This spray keeps the adult insects from laying their
eggs on the plants and kills many of the young insects.

EXPERIMENTAL PROCEDURE.

Three kinds of sprays containing copper were used in the experi-
mental work reported here: (a) Ordinary Bordeaux spray, pre-
pared by mixing milk of lime and copper sulphate solutions; (0d)
Pickering spray, prepared by mixing a saturated solution of lime-
water with a dilute solution of copper sulphate; and (c) a barium-
water spray, prepared by mixing barium hydroxid with a dilute cop-
per sulphate solution. These sprays are discussed fully in United
States Department of Agriculture Bulletin 866.

The yield data were obtained from the two middle rows of a 4-row
plot. Care was taken to select for these experiments plants which
were as free as possible from late blight, mosaic, leaf roll, ete. The
tubers from six plants receiving the same treatments were placed in
a sack and immediately taken to the laboratory for analysis. For
each analysis six medium-sized tubers were selected from the sam-
ple and the analyses were made the day on which the tubers were
dug. All of the samples were run through a Herles press which gives
a very finely divided product. All determinations were made in
duplicate, the average figures being recorded in the tables. With
the exception of the 1921 data, which include detailed analyses, only
solids, starch, and total nitrogen determinations are reported.

Solids, ash, insoluble ash, sugars, total nitrogen, and phosphorus
were estimated by the methods of the Association of Official Agri-
cultural Chemists (3). Starch was determined by the Herles method
(23) which depends upon the conversion of the insoluble starch to
a soluble starch by means of hydrochloric acid and a reading of the
percentage of soluble starch in the polariscope. Copper (9) was
estimated on 10 grams of the dried sample by the colorimetric pro-
cedure, using potassium ferrocyanid. Soluble nitrogen, soluble phos-
phorus, ammonia nitrogen, coagulable nitrogen, and nitrogen as
monoamino and amid nitrogen were estimated on water extracts
of the finely-divided samples of tubers as previously outlined by the
writer (10). The pH data were obtained on the water extracts of
the tubers, using the colorimetric procedure of Clark and Lubs (7).

RESULTS OF EXPERIMENTAL WORK.
CHANGES IN COMPOSITION OF TUBERS DURING GROWTH.

During the season of 1921 tubers from four varieties of potatoes
grown at Presque Isle, Me., were analyzed. Some of the plants
had been sprayed with copper sprays, while others had not. The
tubers were analyzed at various periods during their growth in order
to determine when the influence of the copper sprays was exerted,
and also to show the changes that take place in the composition of
American-grown tubers during their development. These data are
given in Table 1.

8

BULLETIN 1146, U. S. DEPARTMENT OF AGRICULTURE.

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COPPER SPRAYS ON IRISH POTATO TUBERS. 9

The proportion of solids in most cases showed a gradual increase
during the growth of the tubers. With the exception of the Green
Mountain sample, the proportion of solids was higher in the tubers
from copper-sprayed plants than in those from the unsprayed plants
at the time of the first analysis, that is, when the tubers were less
than an inch in diameter. This indicates that the effect of the copper
was exerted very early in their development.

The solids for all the tubers from the Bordeaux-sprayed plants
averaged 18.63 per cent; for all those from the unsprayed plants,
17.87 per cent; for all those from barium-water-sprayed plants, 19.58
per cent; and for all those from Pickering-sprayed plants, 18.29 per
cent.

The following average ash figures were obtained for all the samples
analyzed: Tubers from unsprayed vines, 0.87 per cent; tubers from
Bordeaux-sprayed plants, 0.88 per cent; and tubers from Pickering-
sprayed plants, 0.85 per cent. The percentage of the total ash found
as insoluble ash decreased in most cases during the growth of the
tubers.

The pH data obtained on the water extracts of the tubers showed
no significant change.

The proportion of total nitrogen, which increased during the
growth of all four varieties of tubers, was somewhat higher for the
tubers from copper-sprayed plants than for those from the un-
sprayed plants. The percentage of nitrogen was higher for the
tubers from copper-sprayed plants than for those from the unsprayed
plants at the time of the first analyses, showing again that the action
of the copper on the metabolic activities of the plant was exerted
very early.

The percentage of insoluble nitrogen in the tubers showed a tend-
ency to decrease during growth. The percentage of soluble nitrogen
increased during growth. The percentage of coagulable nitrogen
increased during growth-in the case of the Irish Cobbler, the Early
Ohio, and the Early Rose varieties, but not in the Green Mountain
variety. The monoamino and amid nitrogen, which includes the
nitrogen not precipitated by phosphotungstic acid, showed a marked
increase for all four varieties during growth. The average per-
centage was slightly higher in the tubers from copper-sprayed plants
than in those from the unsprayed plants. The ammonia nitrogen
content showed no regular change. |

During tuber development the percentage of starch increased some-
what more rapidly than the percentage of solids. A larger percent-
age of starch was usually found in the tubers from copper-sprayed
plants from the first analysis to the last than in the check tubers.
The average data for the content of starch in the tubers were: Bor-
deaux-sprayed, 12.24 per cent; check, 11.73 per cent; barium-sprayed,
12.67 per cent; and Pickering-sprayed, 12.36 per cent.

The sugars,,.calculated as dextrose and sucrose, were present in the
young tubers in relatively large proportions. At the time the tubers
had reached maturity the dextrose had practically disappeared and
the quantity of sucrose had markedly decreased. The unsprayed
tubers of the three early varieties contained a higher percentage of
sugars in the first stages of development and usually a lower per-
centage at maturity than the tubers from copper-sprayed plants.

27475 °—23——_2

10 BULLETIN 1146, U. S. DEPARTMENT OF AGRICULTURE.

This means that the copper sprays may in some way accelerate the
transformation of sugar to starch during the active stages of growth.
The Green Mountain tubers did not show this tendency. The ratio
of sugars to starch decreased greatly during growth, the percentage
of sugars decreasing while the percentage of starch increased. The
ratio of sucrose to dextrose increased during the growth of the tubers,
the dextrose practically disappearing at maturity. At the time the
first and second analyses were made the three early varieties of
potatoes contained a higher percentage of dextrose plus sucrose than
the late variety (Green Mountain). This higher sugar content may
be characteristic of early varieties and may be associated with the
rapid growth which these varieties make. The unsprayed tubers,
with the exception of the Green Mountain, usually showed a higher
ratio of sugar to starch than the tubers from the copper-sprayed
plants.

It is evident that marked changes take place in the potato during
development. Apparently these changes are influenced in some way
by the copper sprays, higher percentages of solids, starch, and
nitrogen usually following the application of copper sprays to
potato vines.

These data may be of value in determining when a potato is
mature. It appears that the sugar to starch ratio, as suggested by
Appleman (2), as well as the ratio of protein to amid nitrogen and |
the percentage of total nitrogen as amid nitrogen, is of value. The
percentage of starch in terms of total solids may be used. Appar-
ently certain changes in the ash constituents may be applied to solve
the question.

EFFECT OF COPPER SPRAYS ON YIELD AND COMPOSITION OF TUBERS.

1917 AND 1918 DATA (MAINE).

In 1916 and again in 1917 potato plants which received copper
sprays gave higher yields than those which received no copper spray.
It was therefore thought that the copper sprays might influence the
eomposition of the tubers as well as the yield. Late blight was
severe in 1917 in this locality but was slight in 1916 and 1918. Dur-
ing the season of 1917 Green Mountain potatoes were sprayed at
Presque Isle, Me., using 5-5-50 Bordeaux, Pickering sprays contain-
ing various amounts of copper, and a barium-water-copper-sul phate
spray containing 0.7 per cent of copper sulphate. Duplicate deter-
minations for solids were made on four samples of tubers from (a)
5-5-50 Bordeaux-sprayed vines (1.25 per cent copper sulphate) ;
(6) Pickering-sprayed vines (0.64 per cent copper sulphate); and
(¢) unsprayed vines grown in the same field. All of the vines were
sprayed seven times during the season, lead arsenate being used on
all of the plants.

The four samples of tubers from the Bordeaux-sprayed vines
averaged 21.45 per cent solids; those from the Pickering-sprayed
vines, 21.49 per cent solids; and those from the check vines, 20.65
per cent solids. Similar results were obtained with this variety of
potatoes in Maine during the season of 1918.

COPPER SPRAYS ON IRISH POTATO TUBERS. ids
1919 DATA.

Arlington Experimental Farm, Va—The 1919 experiments at the
Arlington Experimental Farm of the Department of Agriculture
were conducted on the Early Rose and Irish Cobbler varieties of
potatoes. All plots were sprayed four times, lead arsenate being
applied to both unsprayed and copper-sprayed plots. The field was
uniformly fertilized, using 4-8-4 mixture which was applied at the
rate of 1,200 pounds to the acre. The tubers were analyzed the day
they were dug.

TABLE 2.—Yield and composition of tubers from copper-sprayed and unsprayed
(check) potato plants, Arlington Experimental Farm, 1919.

Yield

from

Variety. Treatment. 2rows, | Solids. |Nitrogen.

each 100

feet long.
Pounds. | Per cent. | Per cent.
Early Rose.....-.-- Nolcopperispray: (checks)\= suo; sasieeos casts aaeieioreyt= 50.0 13. 96 0. 293
Don seseeh! it Bordeaux 4-4-50 (1 per cent copper sulphate)......-. 87.6 14. 30 -272
DO eeeo css eet Pickering spray (0.5 per cent copper sulphate).-...-- 90.3 15. 83 ~325
Trish Cobbler !-.--. INOICOPPErSprayalCHeCk:)a- seman eee nie sc sees ane 124.0 16. 41 - 346
100) Aes 82 ees ease Bordeaux 4-4-50 (1 per cent copper sulphate).--...-- 134.0 18.14 .347
JU eee eae | Pickering spray (0.5 per cent copper sulphate)..-...- 123.0 18. 57 . 364

1 Average of 3 determinations given in each case.

The data in Table 2 indicate that the copper sprays increased the
yield for the Early Rose variety and the solids content of tubers of
both varieties in a locality where late blight is unknown and where
Bordeaux or other copper sprays are not employed generally.

Seven States—The yield and composition of tubers from Bor-
deaux-sprayed and unsprayed plants in seven States (Virginia,
Maine, Minnesota, Pennsylvania, New York, Connecticut, and New
Jersey) are recorded in Table 3. The analytical data are average
figures for 62 samples. Data for Pickering-sprayed plots are
included with the Arlington Experimental Farm results. The tubers
analyzed were from sprayed and unsprayed potato plants grown in
the various States under the direction of plant pathologists and were
sent to the writer by express the day on which they were dug. Arsen-
ical sprays were used on all plots. |

The average increase in yleld per acre of potatoes was 25 per cent.
The average increase of solids in the tubers was from 20.77 per cent,
in the tubers from the check plots, to 21.99 per cent in those from
Bordeaux-sprayed plants, an increase of 5.9 per cent. The average
ficures for pounds of solids of the tubers per acre were 2,591 for the
noncopper-sprayed and 3,430 for the copper-sprayed plants, an aver-
age increase of 32.4 per cent or 48 bushels, due apparently to the use
of copper sprays. It is important to note that the tubers from
Virginia, Maine, and Minnesota, where practically no late blight
occurred, showed the same general results as those from the other
four States, where more or less late blight was noted. This means
that prevalence of late bhg@ht was apparently not the important
factor or necessarily a factor at all. The potato plants grown in

BULLETIN 1146, U. S. DEPARTMENT OF AGRICULTURE.

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COPPER SPRAYS ON IRISH POTATO TUBERS. 13

Connecticut were well infected with late blight before any Bordeaux

spray was applied. All the plants died early; consequently, it is not
surprising that the tubers showed no effect of the Bordeaux spray,
probably because they were formed before the first spray was applied
and were therefore too far advanced to derive any benefit from the
sprays. The New Jersey results for solids were not higher for the
tubers from the copper-sprayed than for those from the unsprayed
plants in the case of all samples examined, although the average
figures were higher for the tubers from the Bordeaux-sprayed plants.
A discussion of the use of Bordeaux spray on potatoes in New Jersey
by Lint (30) is interesting in this connection. He considers the cli-
mate, cultivation, and fertility of the field to be important factors in
determining to what extent Bordeaux is beneficial to the potato. <Ac-
cording to this author, Bordeaux prolongs the life of the vines and
affords the best control of fiea beetle, although increased yield of
tubers does not consistently result from the application of Bordeaux
to potato plants in New Jersey.

It has been the writer’s experience that an occasional sample of
tubers from a check plot will run higher in solids, starch, and nitrogen ~
than a sample from a Bordeaux- or other copper-sprayed plot. This
is the exception to the rule, however, and may be due to the inclusion
among the tubers selected for analysis of a potato or several potatoes
that are not hard and firm. Sometimes one of the tubers in a hill is
a little softer than the rest, probably because the food supply has
been limited or checked in some way. In work of this kind average
figures are undoubtedly the only criterion.

1920 DATA.

Arlington Experimental Farm, Va—tin the spring of 1920 experi-
ments were carried out at Arlington Experimental Farm, using Irish
Cobbler, Early Ohio, and Early Rose varieties of potatoes. Spald-
ing Rose, Gold Coin, Irish Cobbler, and McCormick potatoes were
grown in the fall. A 44-50 Bordeaux spray, a Pickering spray, a
10-10-50 Bordeaux, and a 0-4—50 spray were used. The check plots
and all the copper-sprayed plots received a lead arsenate spray. The
figures reported in Table 4 are the averages for 53 sets of tubers
separately analyzed. ;

TABLE 4.—Yield and composition of tubers from sprayed. and unsprayed potato
plants, Arlington Experimental Farm, Va., August and October, 1920.

| Yield Composition of tubers.
j from
Variety. Treatment. 2 rows,

each 100 | solids. | Starch. | Nit
feet long. : tarch. itrogen.
Early potatoes (August): Pounds. | Per cent.| Per cent. | Per cent.
Trish Cobbler }....... A-4-5O"Bordeaw® ) 585050 ook See Oe 357 19. 91 14, 20 0.372
IDSC see eee Check, (olcop per) Bxn.sc schoo os 321 19, 59 13. 70 . 368
1D be ema IPICKCLING SULA Veen eine cee cece 340 20. 64 14. 50 - 383
ines ee 10-10-50 Bordeaux. -:.............-. 341 20. 42 14. 70 . 367
1) 3 SU See 0-4-50 spray (No copper)..-..-.....-.- 350 19. 85 13. 90 356
a Olea ss: 4-4-50 Bordeaux... 2..2...2...0200-- 217 19.17 13. 90 412
Oe sews Chock (noicoppen)i- cose ee 216 19. 28 13. 90 - 410
Deere. 5225. iPickerins Spray reeeeeraee see aoe eee 211 19, 44 14. 70 . 433
ar! ase *e0ss. 52-)4=4-50 Bordeaux - soi iel ites. oe .c 245 20.18 14, 38 . 367
OP re Wie ce oe. Check @.0:copper) aes 2 2 228 18. 97 13. 60 -326
ot Seiten wooo Pickering Spray sedssoee sees. eee 229 20. 86 14, 83 364

1 Average of 2 sets. 2 Average of 4 sets.

14 BULLETIN 1146, U. S. DEPARTMENT OF AGRICULTURE.

TABLE 4.—Yield and composition of tubers from sprayed and unsprayed potato
plants, ete—Continued.

Yield Composition of tubers.
from
Variety. Treatment. 2 TOWS,
ieatlan Solids. | Starch. | Nitrogen.
Late potatoes (October): Pounds. | Per cent. | Per cené. | Per cent.
Spalding Rose....... 0-4-50 spray (Mo copper)....-..------ 153 19. 36 16. 80 0. 406
DO? | 9 hes ces Pickering spraye eo aeecie. tes 5243 221 21.48 19. 20 397
ID OF eee ee eee 44-50 Bordeaux... ...-2..--.-2-2--- 250 Qa eds eae . 430
DOSES Seen a poet Check @Moicoppen)a-setean 2 ene 248 1OF8Psig sh. Pee! . 409
Goldi@oine= =~ x.55-- 4-450 Bordealixcr ae. 35. e aes a 242 22. 09 17.00 - 485
ID Ose aera 0-4-50 spray (no copper) -..-----.---- 232 PALS wal eee Seated 461
IDO 2s Stick 53 Pickering Sprays. 2 jack sec ee Pee 296 23. 80 17. 90 . 457
DO see reene tees Check (m0 COppeEyis-5 ees. =-< soe 294 19. 52 14. 50 444
Trish Cobbl CS) ripe oe 44-50 Bordeaux......-....--------- 303 22. 69 17. 20 . 443
Bot te Bae 0-4-50 spray (no copper)..---------- 245 20. 14 15.13 . 400
Do 1 See ooe eee 10=10—50 Bordeatixess- 22 22 1 ee 291 22. 43 17,15 - 444
DO F265) hes. 48 Pickeringispray =. 2. saaee ec aa aaes 261 21. 92 16. 73 -443
DO ree eae ee Check: (0) copper) s- 6-2 ee eee 288 20. 66 15. 68 . 429
MeCormick? = _ =... - Cheek /(mo copper) & 2 5c 2522-46 245 21. 72 15. 85 430
DOr ee Pe Q-4-50 spray (mo copper) ------------ 237 21. 36 15. 50 419
ID Orisa. eet Pickerine Sprayecoete a see ee ee 259 21. 88 15. 90 - 456
ID Ope ee Ee cress 2 44-50 Bordeaux ..-....2...---.------ 241 21. 32 15. 50 . 436
1B) Oe een LO=10=500B ord cai. eee oe eee 226 21.47 15. 75 . 457 -
1Average of 2 sets. 2A verage of 3 sets.

The 10-10-50 Bordeaux spray showed no particular advantages
over the 44-50 Bordeaux spray or the Pickering spray in either the
early or late tests. The vines receiving the 0-4—50 spray, which con-
_ tained no copper but did contain lime, usually showed yield results
lower than those of the checks, but the results of the analyses of the
tubers usually agreed rather closely with those obtained for tubers
from the check plants. The yield data are variable, but on an aver-
age are higher for the copper-sprayed than for the check plants.
The data for solids, starch, and nitrogen are generally higher for
the copper-sprayed than for the lime-sprayed or check plants. This
indicates that copper is the essential constituent of the spray.

Maine, New York, New Jersey, and Penns yloania. —Thirty-three
samples of tubers from Bordeaux-sprayed plants from Maine, Penn-
sylvania, and New Jersey and from Bordeaux-sprayed and Bordeaux-
dusted and unsprayed potato vines in New York (Table 5) were
examined. All of the plants were sprayed with an arsenical. San-
der’s Bordeaux dust was used. The sprays and dusts were applied
five times during the season.

TABLE 5.—Composition of tubers from sprayed and unsprayed potato plants,
Maine, Pennsylvania, New Jersey, and New York, 1920.

Composition of tubers.

Source. Variety. Treatment.

Solids. | Starch. | Nitrogen.

Per cent. Per cent. | Per cent.

Mame: 2222.5 se irishiCobbler:- 5-e2----- 5-5-50 Bordeaux...-......-- 3 20K4 15.9 0. 367

1D Oe ee a 2 ee Goss eS See Check (no copper).........-- 18. 39 13. 80 -o08

DOR sees 8 nae Spalding Rose....-...... 5-5-50 Bordeaux .-.-...2..:. 18. 23 13. 80 . 356
IDO 2 ose ae SRS ee GOs at ee Check (no copper)..-........- 18.13 13. 95 319

DO 255555288e iMeCormick. 22-3: esas eeo- 5-5-50 Bordeaux.-.-.......- 21.70 16. 80 . 371

DO oe ee ees GOS Bes Sele ee Check (no copper)..........- 20. 91 16. 00 - 356
DOSS SSF Se Marly, Hoseteo: J-hee eee 5-5-50 Bordeaux. .--....-.:- 21. 65 17. 00 sol6 =

DORE e es oes GOR acetic su ceeee Check (mo copper)........... 21. 93 16. 95 . 339

“4
a

COPPER SPRAYS ON IRISH POTATO TUBERS. 15

TABLE 5.—Composition of tubers from sprayed and unsprayed potato plants,
Maine, Pennsylvania, New Jersey, and New York, 1920—Continued.

Composition of tubers.

Source. Variety. Treatment.

Solids. | Starch. | Nitrogen.
Per cent. | Per cent. | Per cent.
Pennsylvania....| Blight Proof ..-.-.....-- 5-5-50 Bordeaux............ .5 20. 0. 395
1D Tis Soe eee el eee Oe ee ees Check (no copper).......-..- 21. 92 17. 30 . 353
Gee est | Dibble Russet........... 5-5-50 Bordeaux........-.-- 21.79} 16.75 362
1) ee ae ee a Ko Geena SE eine tees Check (no copper)....---.--- 23. 36 18. 53 . 334
Dore es wee Blight Proof Union Co..| 5-5-50 Bordeaux...........- 24, 42 21. 04 . 340
12a ee OM ee a aie Check (no copper)......--.-- 19. 80 15. 20 . 363
New Jersey...... American Giants!....-. 44-50 Bordeaux...........- 18. 20 12.73 - 334
1D Yaya cyie ee Sees 2] 8 EN 6 Voy Dis te one te ky Sema Check (no copper)..........- 18. 33 12: 35 . 290
New=sY Ork- 22... Variety 9 (Wilkes)...-.. 44-50 Bordeaux.........-.- 23. 12 19. 50 274
Dip ae ese. 125 2. dows 5 Sarees ee Bordeaux dust...........-.. 22. 96 19. 00 311
DOr cue as c| ao... -% GOs ee Ae Check (no copper)......--.-- 23. 16 19. 10 . «297
1) oe ee Variety 9 (White)....... 4-4-50 Bordeaux.........-.- 22.74 18. 60 412
IDO, Ree er ees Goss) fries Seo se iB Ordeatex GuSit G5. ose cose 22. 74 18. 40 - 403
WOME nae cc lEe nee don 2 Wate Seen Check (no copper)..........- 22. 35 18. 20 . 367

1D ace Heavyweight (Kd-
Wards) 252 eee ase IBOLdealixs GuSteesee acess 23. 80 18. 90 - 401
IDO as ae GO Ui a: ees aha Check (no copper)........--. PATE 17.30 - 356
DORSs see << Goldson'e J sseeeek=s 4-4-50 Bordeaux............ 28. 16 22. 30 - 455
ID) eee et ee ar GOssre see eae IBOLdealxGUSt leet see seen ee 26. 42 21. 00 - 478
ID On ee eee, Cc fo Me Ce Peer ae Check (no copper).......-..- 26. 62 21.40 - 416
IDO) oR ee (en i RT UTS EP a a 44-50 Bordeaux...........- 24. 03 19. 60 - 230
IDO SA cee eee nea a aearcs Ser sty a Check (no copper).-....-..-- 20. 34 15. 40 . 280
DD Ona sis5 22 =: Dibble Russet (Slayton). Bordeaux dust............-- 27.61 22.75 348
LD eee ers GOSS see eee Check (no copper)........--- 27.37 22. 80 347

i Average of 2 sets.

For the New York data several varieties of potatoes grown near
Bath and one variety from Geneva were analyzed. From the limited
number of samples tested it is impossible to state definitely whether
Bordeaux dust tas the same favorable effect on the potato plant as
Bordeaux spray has, although the results in Table 5 are not par-
ticularly favorable to the dust, with the exception of those for the
Heavyweight variety. Average figures for three sets grown in New
York gave 24.67 per cent of solids for tubers from Berdeaux-sprayed
plants, 24.04 per cent for tubers from Bordeaux-dusted plants, and
24.04 per cent for tubers from unsprayed plants. The average starch
results for these three sets are 20.13 per cent for tubers from plants
recelving Bordeaux spray, 19.47 per cent for those from plants
treated with Bordeaux dust, and 19.57 per cent for those from the
check plants. The average nitrogen data for the three sets are:
Tubers from Bordeaux-sprayed plants, 0.88 per cent; tubers from
Bordeaux-dusted plants, 0.397 per cent; and tubers from unsprayed.
plants, 0.36 per cent. Comparing all five dusted plots with the five
corresponding checks gives an average of 24.71 per cent solids
against 24.24 per cent, and comparing all four Bordeaux-sprayed
plots an average of 24.51 per cent solids against 23.12 per cent for
the checks. In general, the results for the New York tubers were
higher when Bordeaux spray was used than when no spray was used.

Data were secured for four varieties of potatoes grown in Maine,
two varieties from Pennsylvania, one variety having been grown in
two different places, and one variety from New Jersey. Three of
the four samples of tubers from Maine were higher for Bordeaux
and they averaged 20.51 per cent solids from the Bordeaux-sprayed
plants and 19.84 per cent from the check plants. Two of the three
sets of tubers from Pennsylvania were higher for the Bordeaux

16 BULLETIN 1146, U. S. DEPARTMENT OF AGRICULTURE.

samples and the average solids content for the three sets was 93.92

per cent from the Bordeaux-sprayed plants, as compared with 21.69
per cent for the tubers from the check vines. The two samples of
the American Giant variety from New Jersey had practically the
same content of solids and the tubers from the Bordeaux-sprayed
vines had but slightly higher contents of starch and nitrogen.

The average results for the tubers from the four States show that
the general effect of the copper sprays is to increase the solids
content of the tubers.

1921 DATA,

Presque Isle, Me—The 1921 experiments were conducted at

Presque Isle, Me., to determine the influence of Bordeaux, Pickering,
_and barium-water sprays, all containing copper, on the yield of
tubers. The data were compared with data obtained from check or
noncopper-sprayed plants in each case. All of the plants received an
arsenical spray.

TABLE 6.—Yield from 3 varieties of potatoes, Presque Isle, Me., 1921.

| Front plots. Rear plots.
Variety. WIRE fe 80 wae ete ie Rk (ar eg ee ETS
Flot | spray used rield.a | Flot Spray used Yield
|
- } |

Aroostook farm: Pounds | Pounds Pounds.

Early Rose..... 2 | Bordeaux..-.-....- 2128 1 | Check (no copper)... 2107 |=255.-

Early Ohio..... 7 = ee deascr) Gs5 me 2106 Seeks d022. Ase 2\995}5-6- 238

Trish Cobbler...| 5A | Check (no copper)... 868 | 5B-|..<.- it eee eee eee: 724 1,592

13 3 as eee 6 | Bordeaux.......... 864 7 | Pickering -.....-....| 780 1,644

en Moun- | 8A | Check (nocopper).-| 1,020} 8B | Check (mocopper)... 821 1,841
in.

Doss4- =: 9 | Bordeaux......-... 1,070 tO 3} Baran: . 53s). Sse 850 1, 920

Dos 11A | Pickering.........- 1,046 | 11B |....- do ee eee 909 1,955

Kneeland farm:
Ggeen Moun-| 1A | Bordeaux.......... 7234. 1B), Bordeaux 52-7 355. 636 2,751
ain.

DOs sss. 2A | Proprietary spray-.- 63 2B | Proprietary spray... 707 2, 682

DOs se ee 3A | Check (no copper).. 583 | 3B | Check (no copper)... 532 2,376

Dore Ss 3C | Barium spray....-- 671 | 3D {| Bariumspray...-..-- 733 | 2,859

Dine ae 4A | Bordeaux.-........ 732.| -4B | Bordeaux -:_......:- 660 |.--..--.-

Doo 2 FACT Pickerme 2225 _s oe 664 | 5B | Pickering........... 716 | 2,760

Bey = 27 sae 6A | Check (no copper)... 648 | 6B | Check (no copper)... G13,|- etic

1 DY ees 6C | Barium spray..-.-- 744 | 6D | Barium spray-....... Tih ie eee

Wot. eee! 7A | Proprietary spray. - 625 | 7B | Proprietary spray-..! TEISK CE Ste
i

1 Yield from 2 rows, 300 feet long, in case of Aroostook farm potatoes; yield from 2 rows, 225 feet long,
in case of Kneeland farm potatoes.

2 Yields from 50 hills each.

8 Yield from 2 plots in case of Aroostook farm; yield from 4 plots in case of Kneeland farm.

From the data from the Aroostook farm and from the Kneeland
farm (Table 6) it is evident that the copper-sprayed plants generally
gave an increased yield of tubers. In 1921 there was no late blight
(Phytophthora infestans) in northern Maine. The reason for using
copper sprays in this locality is to control this fungus. Increased
yields seem to follow the application of these sprays in seasons when
no late blight was prevalent.

PROPORTION OF TUBERS TO VINES PLUS TUBERS.

The weights of vines and tubers were determined at Presque Isle)
Me., at the time the analyses of the tubers reported in Table 1 were

made. As a rule, eight healthy potato plants were pulled and the}

Ne ee ee a ee ee ee ee ee ee |

a Aa eo ee er oe hee

.
;
|

COPPER SPRAYS ON IRISH POTATO TUBERS. 1%

tatoes under them dug. The dirt was shaken from the vines and
the adhering roots, and the soil was wiped from the tubers. The
vines and tubers were then weighed together and separate weighings
of the tubers were made. From these data the percentage of tubers ©
in terms of the total weight of the vines plus tubers was calculated.

TABLE 7.—Weight of potato vines and tubers, Presque Isle, Me., 1921.

: Bordeaux-sprayed. | Pickering-sprayed. No (Gheeky 7 ay
ae Date : :
Variety. weighed. |
Vines.| Tubers. | Vines. | Tubers. |Vines.| Tubers.
| |
| 4

| Lbs. | Lbs. | Perct.| Lbs. | Lbs. | Perct.| Lbs. | Lbs. | Per ct.
¥eish Copbler:.... - ----..-==- July, 262 | 7-50))-*3.00,| 28.5.) 97.25, |=.2.50.} 25-6. |, 9.75.1 22.50 20. 4
Tees ees Oe ee De pee Aug. 152) 5.25 )°5275.) 52:3) 7-00 | 7200 | 50°07) 5525 | 5.25 50. 0
US Rae See ee eee Sept. 173| 3.50} 8.50] 70.8| 3.25; 9.00] 73.5] 2.50] 11.25] &81.8
Harly*ivose: 5-25 -4 &leosb Na Pay Pd AT AGM | ry i gS Seed Per eaters 6.00} 2.75 31.4
ES Se OE Pane Aug. 192] 6.75 | 6.75} 50.0 |.....-- Pes Cee 6.75 | 6.75; 50.0
Vee = = ee Se eee ea Sept. 143}] 6.25 | 13.75 | 68.8 |.....-- eesti ps |e eS 4.75 | 13.00 | 673.2
esivhy. Obi os E Rae 7S 21 Y 6507275 | QOET Eee Pisce Th OS 8.25] 2.50] 23.3
eee eee a Aug. 182] 7.25 | 6.75} 48.2 |....... [sa5255 Bete 8.25 | 8.00 49.2
yet SoU Seg Sept. 133] 4.25] 8.25] 66.0 |.....-- ee haere 4.00} 8.00! 66.7
Green Mountain........--- Aug. 231] 10.75 | 4.00} 27.1-/#11.50 | #5.00 | 430.3 | 8.50 | 2.75 | 24.4
LG eels Seen oe eee Aug. 2372] 7.00} 5.50] 44.0] 5.25] 4.00] 48.2] 5.75) 4.00 41.0
Tee eee ae EATER 29 Ee EE Sees 28 44.25 |44.00 |} 448.5 | 5.00) 5.00 50.0
= CLR ee Sept. 203 3.38 | 7.38 | 68.6 | 44.00 | 48.75 | 468.6 2. 25 | 7.25 | ©76.3
He OOS Se te Septs 205). 252)| ee [ern diab P10! 50P 7.4 (LL) lee Mies

[PS ae Pee ae domss etry) | 59.50 | 576.0 |

1 Date of first analysis.

2 Date of second analysis.

3 Date of last analysis.

¢ Barium-sprayed.

* Nickel-sprayed. 1

6 The check vines at time of last analyses were dead or partly dead and therefore lighter than the
vines of the copper-sprayed plants. These figures are not comparable with the other data.

The data presented in Table 7 show that when the potato vines
were growing, that is, while they were green, a higher propor-
tion of tubers to vines plus tubers was usually found in the copper-
sprayed than in the unsprayed plants. At the time the first weigh-
ings were made, as soon as the tubers were about an inch in diameter,
the infiuence of the copper sprays was shown. The results in Table
7 indicate that the stimulating effect of the copper is largely shown
by the increased weights of tubers rather than by increased weights
of the vines and that it is exerted early in their development. As the
tubers are the storehouse for the starch formed in the leaves, the per-
centage of starch in the tubers would naturally increase. At the
time the last analyses of the tubers were made the unsprayed vines
had partly dried and therefore were lighter than the corresponding
vines for the copper-sprayed plants. The data for these samples are
not directly comparable with the rest of the data.

INFLUENCE OF STRENGTH AND NUMBER OF APPLICATIONS OF COPPER SPRAYS
ON COMPOSITION OF TUBERS.

Several samples of tubers grown in New Jersey during the season
of 1920 were analyzed for solids and nitrogen. Some of the plots
from which samples were taken had received a 10-10-50 Bordeaux
spray; others had received a 5-5—50 Bordeaux spray; a third plot
had been treated with a 24-24-50 spray; while some of the plots had
received no copper spray. The results for solids and nitrogen in

18 BULLETIN 1146, U. S. DEPARTMENT OF AGRICULTURE.

the tubers from copper-sprayed plants were: 10-10-50 spray, 17.9
per cent solids and 0.38 per cent nitrogen; 5-5—50 spray, 18.5 per cent
_ solids and 0.34 per cent nitrogen; 24-24-50 spray, 20.1 per cent solids
and 0.33 per cent nitrogen. The check tubers contained 18.3 per cent
solids and 0.33’ per cent nitrogen. The tubers from the plots receiy-
ing the 23-24-50 spray were highest, and those from the 10-10-50-
sprayed plots were lowest in solids.

These results suggest the possibility that a certain proportion of
copper in a spray gives the maximum-stimulating effect in this local-
ity and that a spray containing a greater proportion of copper may
have a toxic rather than a stimulating effect. Tubers grown at
Arlington Experimental Farm in 1920 from vines that were sprayed
with a 10-10-50 Bordeaux spray (p. 18) seemed to have no advan-
tages over the tubers from plants sprayed with a 44-50 Bordeaux.
It is, of course, probable that the stimulating effect of the copper
varies with the climatic conditions, variety of potatoes used, etc.
Tubers from vines in New Jersey sprayed with a 5—5-50 spray eight
times during the season were compared with tubers from vines
sprayed only four times with Bordeaux spray of the same strength.
The average data for four sets were 18.6 per cent of solids and 0.37
per cent of nitrogen in the tubers from vines sprayed eight times and
19.1 per cent of solids and 0.35 per cent of nitrogen for the tubers
from vines sprayed only four times. These variations are small and
may not be due to the differences in the spray applications. These
data also indicate that too much copper may have reached the vines
by the eight applications, whereas the amount of copper present in
the four applications was nearer the quantity required to give the
best protective effect or a maximum stimulation to the plants.

INFLUENCE OF ENVIRONMENT ON COMPOSITION OF TUBERS.

The following data were obtained during the 1919 season. Early
Rose tubers grown in Connecticut contained 21.59 per cent solids and
0.38 per cent nitrogen and the same variety grown at Arlington Ex-
perimental Farm contained 15.83 per cent solids and 0.33 per cent
nitrogen. Irish Cobbler tubers grown in Connecticut contained 22.28
per cent solids and 0.43 per cent nitrogen, while the same variety
grown at Arlington Experimental Farm contained 18.57 per cent
solids and 0.36 per cent nitrogen. Dibble Russets from New York
contained 25.38 per cent solids and 0.39 per cent nitrogen and thesame
variety grown at Mt. Carmel, Conn., contained 21.24 per cent solids
and 0.380 per cent nitrogen. Early Ohio tubers from Minnesota con-
tained 22.79 per cent solids and 0.48 per cent nitrogen and the same
variety from Connecticut, 20.52 per cent solids and 0.48 per cent
nitrogen. These results again suggest that the composition of the
tubers is infiuenced by the environment.

Although these tubers were not grown from the same stock, the
results in each case seem to indicate that a northern tuber is higher in
solids than asoutherntuber. Thismay explain why a northern grown
potato is a better seed potato than one grown in the South. The data
also show that there is a decided variation in the percentage of
solids in tubers of different varieties grown in the same locality.
In this connection it is interesting to recall the findings of LeClere
and Yoder (27) who, working with wheat in four different parts

%
;
;
‘=
..

COPPER SPRAYS ON IRISH POTATO TUBERS. 19

of the United States, concluded that environment rather than hered-
ity is the major factor in determining the physical and chemical
characteristics of the wheat crop.

COPPER CONTENT OF VINES, STEMS, ROOTS, AND TUBERS OF SPRAYED AND UN-
SPRAYED PLANTS.

Copper is widely distributed in nature. Apparently all plants
and animals contain small amounts of this metal.

In 1816 Meissner (35) reported that copper was present in the ash
of various plants in small quantities. Dieulafait (72) in 1880 showed
that the amount of copper present in vegetation was largely de-
termined by the nature of the soil.

Lehmann (28), in 1895 and 1896, estimated the copper in wheat,
rye, barley, oats, maize, buckwheat, potatoes, beans, linseed, apricots,
pears, breads, cocoa, and chocolate. He found that only in the
plants grown in soil relatively high in copper does any appreciable
amount of copper get into the plant. The species of plant is ap-
parently of less importance than the copper content of the soil in
determining the amount of copper found in the plant. In wheat
and buckwheat the copper was chiefly in_ the stems and leaves,
little being found in the fruits and seeds. Therefore a high copper
content in the soil does not necessarily mean that much copper is
present in the grain and seed. The form in which the copper exists
in plants is not known. Lehmann gives data showing that the
quantity of copper in any species of plant varies with the individuals
of the species, even when grown on the same soil in the same year,
and under similar conditions.

MacDougal (34) examined microscopically and analyzed various
parts of a ‘tree which had grown in copper-bearing soil. He found
metallic copper in relatively large quantities throughout the tissues,
indicating an absorption of copper by the tree over a period of years.

TABLE 8.—Copper in tubers from copper-sprayed and noncopper-sprayed plants.

[ Parts per million.]

Copper in dry tubers from vines treated with 1—

arsenate |Bordeaux| Picker- | arsenate

|
Variety. | Place grown. Calcium Lead Ghee
(no cop- | spray. jing spray-.| (no cop- per)
;
|

Spalding Rose........... | gk ea 8 | in 15) Po Cee. Ree ee

Farm,
Trish es See ae ee ie. 3 Goeth Ms HAY ol 11 13 Oil? ae. tsp eee 2
3 eae ae Le ee ee ats G (ener SL aes ee 11 15 DY 50 Pe ge Ye Sr ae
Do Lt See eee ea ae 7 ee ea! GO se 5 es 14 16 Dt A) i ee eek
worse: 05. oo) ee | oe S| maa ae Uy a 11 14 BS 'f. fete as Be ee
TO foes 2 ee ED aisha
American Giant.. ae eee | Nawsherseyis? 2252s Sluis oS oN wh on ees poe 10 11
Gi bo Uy Bases oe ee
Biaeky Orage se, Pe Pe Monnesoba 2 2eeto2' 22 ie olte ae 10} }-2 Ae eee 13
Green Mountain .-....... Presque Isle, Me. --.-:._- EE. le BO fe 322 a A ees 9
Magnum Bonum......... IN@W. WORK ose) oat lS | 5 SRR He LTE ea ee ee 10
Pebble Basset... 222-222]. 22. 05 (eS gS Sa ee ae K ; : RaeaRs Aaa 2282 aes =
ennsylyanin. 2 sees) ee [re eae fe eee 10
Waurmouceenme ceteris ff) ipre PO ear it Roe | ERSTE MS _ 2e | 10 | RIES 10

1 All of the copper-sprayed plants received an arsenical spray as well.
2 Sprayed twice.
3 Sprayed 6 times.

20 BULLETIN 1146, U. S. DEPARTMENT OF AGRICULTURE.

Some of the tubers from copper-sprayed and from unsprayed
potato plants grown at Arlington Experimental Farm during the
season of 1920 were analyzed for copper (Table 8). The average
figure for tubers from copper-sprayed plants grown at Arlington
was 13.5 and for those from plants receiving no copper, 11 parts of
copper per million. Average figures for tubers grown in other
localities were 10 parts of copper per million for those from both
the Bordeaux-sprayed and unsprayed vines. The writer (71) has
shown that tubers contain only traces of copper, while the roots,
stems, and leaves of potato plants contain appreciable quantities.

During the season of 1921 three separate samples of leaves, stems,
and roots from four varieties of potatoes were analyzed for copper.
At the time of each analysis nine plants were dug and immediately
taken to the laboratory, where they were washed in water. The
plants were next dipped in 4 per cent hydrochloric acid for 80
seconds and then held in water for 5 minutes. This process was
repeated three times. The plants were finally placed in a large tub,
covered with water, and allowed to remain overnight. The next
day all of the plants were thoroughly rinsed in running water and
then in distilled water, after which they were dried in the air. The
leaves were used for analysis directly. The stems and roots of all
the samples were carefully scraped with a knife to remove the outer
layers of plant tissue. The scraped samples were then washed in
distilled water to remove any possible copper contamination during
the scraping process. Five grams of the dried sample were used
for copper analysis by the colorimetric method. The acid and water
treatments apparently removed all the external copper from the
plants, as the results for copper in the roots are higher than those
for copper in the leaves.

TABLE 9.—Copper in leaves, stems, and roots of Bordeaux-sprayed and un-
sprayed potato plants, 1921.

(Parts per million on the dry basis.)

Leaves. Stems | Roots.

aieeine ep ue Sprayed | . U2=_ | sprayed | . U™ . | Sprayed | . UE

: praye@ | sprayed | PPTAY€* | sprayed | PPTAaYe* | sprayed

plants plants. plants. plants. plants. plants.
ues stanly: OhiO- 244-2 See hace ee 6.6 5.0 3.4 2.6 6.7 3.8
OSs wharly ROSC)— a3. sccinc sack es 13.0 10.0 6.6 4.0 18.4 6
Doss | sais Cobbler’. 222. Sesh ee 11.0 9.0 9.3 8.9 21.5 16.9
Do.-.| Green Mountain 2..-......-....- 8.0 7.4 4.6 5.8 7.5 8.0
Auresisenl Barly @hio..-.2)4.65..0.. ee 10.6 12.0 9.4 S41}: 2 wees 9.9
1D Ose | tbarhystiOSe se .eke oo aes ooo ce 9.6 9.6 6.0 8.0 8.6 10.4
Do imishiCopplers. saa cc eb ace 12.0 8.0 7.6 10.2 8.4 8.0
Do...| Green Mountain 2.--............ 11.4 10.6 7.0 7.0 10.1 8.6
Senta lonmlarlyshOhiOn =. sas2e 8 feces eae 17.3 10.0 14.0 THIS AaHle 26.0 13.8
OLvN Barly AROSes. = coo se cc coe ce eee 13.0 9.0 5.0 8.5 19.4 9.1
Done inshiCopblersss- een. Sse ao 11.0 9.0 8.1 6.3 8.3 9.0
Do...| Green Mountain.-.-.-...-.....- 9.0 6.8 6.3 4.4 9.1 6.6

1 Sprayed with Pickering spray. 2 Sprayed with barium-water spray.

The data for the leaves, stems, and roots, given in Table 9, show

certain variations, but in the majority of the samples the correspond-_

ing figures for the copper-sprayed were higher than. those for the
unsprayed samples. The roots held the most and the stems the least

;
:
t
;

ee plete

COPPER SPRAYS ON IRISH POTATO TUBERS, 21
: \
copper for all four varieties of potato plants. The three early vari-
eties of potato plants contained more copper than the Green Moun-
tain, a late variety. An appreciable quantity of the copper was
present in all of the check plants.

GENERAL DISCUSSION.

In the case of copper sprays it is generally recognized that a small
quantity of copper is gradually rendered soluble either by the juices
of the plant or by the carbon dioxid of the air, and this copper thus
rendered soluble may protect the plant and may stimulate its meta-
bolic activities. The intensity of action of the copper compounds
varies with the kind of plant used and with the quantity of copper
applied. This difference in the ability of plants to withstand the
action of copper sprays was illustrated by the drastic effect of Pick-
ering sprays (9) on the grape and apple compared with its favorable
action on the potato and cranberry. The influence of environment,
soil, climate, etc., must also be considered in this connection, as a
Bordeaux spray may be used on a certain plant in one section of the
country but can not be used without severe injury on the same plant
in another locality. The data show that increased growth and tuber
formation of the potato following the use of copper sprays may be
secured. The fact that a certain amount of hopperburn was present
in most of the fields where these tests were conducted is recognized.
It was not severe in any case and practically none was observed on
the plants at Arlington Experimental Farm. Some of the increased
yield of tubers from copper-sprayed potato plants was undoubtedly
due to the action of the copper sprays in controlling potato leaf-
hoppers and thereby reducing hopperburn. It is difficult to explain
it all on the basis of protective action alone.

Analyses of grapes from copper-sprayed and from unsprayed vines
reported by the writer (9) showed that the composition of the grape
had apparently been altered by the application of the copper sprays.
Evidently copper sprays alter the composition of the potato and the
grape and there is no reason to believe that their action is restricted
to these two plants.

Several theories have been advanced to explain the increased yield
of tubers from Bordeaux-sprayed: potato plants:

(a) Bordeaux spray increases the transpiration rate of potato
plants, according to Lutman, Duggar, and others. This effect would
apparently be an advantage in wet seasons or wet localities but a dis-
advantage in dry seasons or dry localities. Differences in humidity
cause differences in the transpiration of plants, and this may react
on the growth of the plant and the composition of the tubers.

(6) It is possible that changes in the rate of respiration or in the
general metabolism of potato plants may follow the application of
copper sprays. A small quantity of copper may be absorbed by the
plant and stimulate it to increased activity. There are several ex-
amples of stimulation brought about by a small amount of a sub-
stance which in large quantities is toxic. There is evidence that
copper stimulates some plants and the fact that stimulation can not
be shown to exist does not prove that it is not there. Analyses of
the leaves, vines, and roots of sprayed and unsprayed potato vines
in most cases showed a higher proportion of copper in the leaves,

79. BULLETIN 1146, U. S. DEPARTMENT OF AGRICULTURE.

stems, and roots of the sprayed potato plants than in those of the
unsprayed plants. :

(¢) Variations in sunlight or stimulation resulting from the appli-
cation of copper sprays may influence the photosynthetic processes.

(d) The copper sprays protect the vines which are thus kept freer
from tip burn, disease, and insect injury. Vines treated in this way
are therefore more vigorous and their tubers may show an increase
in solids, as well as in yield. It is now recognized that potato leaf-
hoppers are the direct cause of hopperburn and that Bordeaux
mixture repels the hoppers. Bordeaux spray is a protection against
potato leafhoppers, flea beetles, and other insects, as well as against
fungous diseases. It is not clear why the tubers should be higher in
solids unless it is simply taken for granted that a vigorous plant
produces a tuber higher in solids than a less vigorous plant. There
is a possibility that the protective effect of Bordeaux is the only effect
produced, but copper salts have such a pronounced effect on all living
tissue that a stimulation is generally suspected and even accepted by
many investigators in this field.

Some suggestions from the recent work of Sherman and his co-
workers are of interest in this connection. They studied the effects
of certain antiseptics upon the activity of amylases (42), all of which
were very sensitive to copper sulphate. They also studied the influ-
ence of certain amino acids upon the enzymic hydrolysis of starch
(43), finding that glycine, alanine, phenyl! alanine, or tyrosine caused
an undoubted increase in the rate of hydrolysis of starch by purified
pancreatic amylase, commercial pancreatin, saliva, or purified amy-
lase. The favorable effect is not due to any influence on hydrogen
ion concentration nor to a combination of the amino acid with the
product of the enzymatic reaction. The addition of 1 per cent of
these amino acids was shown to be a very effective means of pro-
tecting the enzyme from the deleterious eftect of copper sulphate and
may even serve to restore to full activity any enzyme which has been
partially inactivated by copper. Arginine and cystine have a favor-
able influence upon the hydrolysis of starch by purified pancreatic
amylase, while histidine and tryptophane do not (j4). The effect
of histidine and tryptophane differs from that of all the other amino
acids studied, possibly because of their heterocyclic structure or their
position in the protein complex which doubtless constitutes either
the enzyme itself or an essential part of it.

There is evidence that a somewhat larger quantity of copper is
present in copper-sprayed potato plants than in the unsprayed plants,
and also that the proportion of amino and amid nitrogen in potato
plants increases during growth. Data showing that copper had a
favorable effect on the yield and composition of tubers were obtained.
Possibly the amino acids protect the cell activity from any toxic
action of the copper, thus permitting the copper to exert a stimulating
effect on the cells.

It is recognized that it would be desirable to have data showing
the normal variation for the different varieties of tubers under the
same conditions, but time did not permit the securing of such data.
Analyses of several hundred tubers, both copper-sprayed and check,
were obtained and the average data from this large number of tubers
should overcome individual variation.

COPPER SPRAYS ON IRISH POTATO TUBERS. iy

The results reported in this paper appear to establish the fact that
copper sprays not only increase the yield of potatoes in various sec-
tions of the country, but favorably influence their composition.? Bor-
deaux sprays, Pickering sprays, and barium-water sprays seemed to
_ give the increased yield and increased solids of the tubers which
apparently depend on the presence of copper in the spray. In addi-
tion to plant-disease control and insect control, the copper appears to
exert a stimulating action on the potato plant.

Bordeaux and other sprays containing copper are usually applied
to the potato to control the late blight. “In some States such a spray
is applied as a repellent to the flea beetle and the potato leafhopper,
thereby reducing the injury to the foliage from these two insect pests
and at the same time lessening tip burn and hopperburn. The im-
portance of the effect of copper sprays on the yield of potatoes, in
addition to their control of diseases and insects, has not been gener-
ally recognized or at least emphasized. Nor has the fact that tubers
from copper-sprayed plants may be stored more satisfactorily—that
is, with less loss from rot—than tubers from noncopper-sprayed plants
been wide y advertised. When, in addition, an increased yield of
potatoes and a higher proportion of solids in them follow the appli-
_cation of copper sprays, important additional reasons for their more
general use become evident.

SUMMARY.

Tubers from copper-sprayed potato plants at the time they were
large enough for analysis (about one inch in diameter) were usually
higher in solids, starch, and nitrogen than the tubers from un-
sprayed vines. ‘The starch content increased approximately 50 per
cent as the tubers matured, while the dextrose disappeared and the
sucrose was materially reduced. The early varieties of potatoes
showed a decrease in their sugar content to accompany an increased
starch content in the copper- -sprayed tubers during the early stages
of development. The proportion of insoluble ash decreased during
the growth of the tubers, although the total ash content remained
constant. The total nitrogen increased. The figures for soluble,
coagulable, and particularly the monoamino and amid nitrogen
increased as the tubers matured.

The proportion of tubers to green vines appeared to be higher for
the copper-sprayed than for the unsprayed plants.

Average data for seven States obtained in 1919 showed the food
value of an acre of copper-sprayed potatoes to be 839 pounds more
than that for an acre of noncopper-sprayed potatoes. Two factors,
increased yield (48 bushels an acre) and an increase of solids (5.6
per cent), are involved.

Some results obtained at Arlington Experimental Farm, Va., com-
paring a 10-10-50 Bordeaux and a 5-5-50 Bordeaux, suggest that
the former spray has no advantage over the latter and may possibly
furnish too much copper for the maximum stimulating or protective
effects. Results from New Jersey, where a 44-50 Bordeaux spray
was applied eight times, compared with results where the same spray

* Attention is called to the experiments of Gray and Ryan, Monthly Bull. Dept. Agr.
State of California, Chemical Number, vol. 10, no. 1, pp. 11-33, 1921. They showed that
the acidity of oranges was reduced by the arsenical spray.

24 BULLETIN 1146, U. S. DEPARTMENT OF AGRICULTURE.

was applied four times, show that the tubers were lower in solids in
the former than in the latter case, suggesting again that too much
copper may have reached the plant for the best results in the absence
of any late blight.

Tubers from several varieties of potatoes grown in a northern State
were higher in solids than tubers of the same varieties grown in a
State farther south.

A larger yield of potatoes was secured from copper-sprayed than
from check or noncopper-sprayed vines. Late blight (Phytophthora
infestans) is eliminated as a necessary factor in the case.

When a lime spray containing no copper was used at Arlington Ex-
perimental Farm, Va., the yields of tubers were decreased. Picker-
ing-limewater spray and a barium-water spray gave practically the
same increase in yield and in solids of the tubers as a Bordeaux spray.
The copper in the spray seems to be the essential factor.

LITERATURE CITED. -

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COPPER SPRAYS ON IRISH POTATO TUBERS. 25

(16) Erwin, A. T.
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The spraying of Irish potatoes. N. C. Dept. Agr. Bull. 40 (1919), no.
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(31) LopEMAN, HE. G. : ;
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26

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246)
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(49)
(50)

(51)
(52)

BULLETIN 1146, U. S. DEPARTMENT OF AGRICULTURE.

PRITCHARD, F. J., and CLARK, W. B.

Effect of copper soap and of Bordeaux soap spray mixtures on control

of tomato leaf spot. Phytopath., 9 (1919) : 554-564.
PRUNET, A.

Recherches phy pee giques sur les tubercules de la pomme de terre.

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Rum, C.

Zur Kenntnis der Giftwirkung der Bordeauxbriihe und ihrer Bestand-
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SCHANDER, R.

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Jahrb., 33 (1904) : 517-584.

SHERMAN, H. C., and CALDWELL, Mary L.

A study of the influence of arginine, histidine, tryptophane and cystine
upon the hydrolysis of starch by purified pancreatic amylase. J. Am.
Chem. Soc., 43 (1921) : 2469-2476.

and WALKER, FLORENCE.
The influence of certain amino acids upon the enzymic hydrolysis of

starch. J. Am. Chem. Soc., 43 (1921) : 2461-2469.

and WAYMAN, MARGUERITE.

Effect of certain antiseptics upon the activity of amylases. J. Am.
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SORAUER, P. ;

Hinige Beobachtungen bei der Anwendung von Kupfermitteln gegen
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STEWART, F. C., Eustace, H. J., and SmRRiIne, F. A.

Potato-spraying experiments in 1902. N. Y. Geneva Agr. Exp. Sta.

Bull. 221 (1902) : 285-268.

Potato-spraying experiments, 1902-1911. N. Y. Geneva Agr. Exp. Sta.
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STEWART, EF. C., FRENCH, G. T., and SIRRINE, F. A.
Potato-spraying experiments in 1910. N. Y. Geneva Agr. Exp. Sta.
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TREBOUX, O.
Hinige stoffliche Einfitisse auf die Kohlersdaureassimilation bei sub-
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Von SCHRENK, H.
Intumescences formed as a result of chemical stimulation. Mo. Bot.
Gard. 16th Ann. Rpt. (1905) : 125-148.
Woops, C. D.
Potato studies. Maine Agr. Exp. Sta. Bull. 277 (1919): 17-82.
ZUCKER, A.
Beitrag zur direkten Beeinflussung der Pflanzen durch die Kupfer-
vitriol-Kalkbriihe. Alfred Miller & Co., Stuttgart, 1896.

ORGANIZATION OF THE UNITED STATES DEPARTMENT OF

AGRICULTURE.
Secretary of Agriculture___________-_______- Henry C. WALLACE.
PESO IEG SCUR CLOT ee a en C. W. PUGSLEY.
Director of Scienttfie: Works... > Bare
Purecior of Regulatory Werle... =.
TET Ge es Ba) RET | aa ac” Sc CHARLES F. Marvin, Chief.
Bureau of Agricultural Economics_________ _ Henry C. Taytor, Chief.
Burcau. of Animal Industry: ~ = JOHN R. Mouter, Chief.
ECA Of ENGI ANOUSET YS Wiitiam A. Tayntor, Chief.
PEE ORE SCT UUCE oe oS = a a W. B. GREELEY, Chief.
eC OT CCIUESEI one eee eS WALTER G. CAMPBELL, Acting Chief.
SALE MILIO NOLS eaten te agg EE Mitton WHITNEY, Chief.
Bureau of Hntomotogy=-— = L. O. Howarp, Chief.
Bureau of Biological Survey. — = E. W. NELSON, Chief.
PUTCO OF PIUUEC FROGWS =. ee eee Se THoMAS H. MaAcDonatp, Chief.
Fized Nitrogen Research Laboratory______- F. G. CotTrett, Director.
Division of Accounts and Disbursements____ A. ZAPPONE, Chief.
Duwasion of Publications_2_ 23 eee JOHN L. Cogss, Jr., Chief.
TRENT EU aE 8 Se eer CLARIBEL R, BARNETT, Librarian.
States hetations Service___.__.- a A. C. TRvuE, Director.
Pederal Hortieuliurat Board. > C. L. Margiatt, Chairman.
Insecticide and Fungicide Board__________- J. K. Haywoop, Chairman.
Packers and Stockyards Administration_____ CHESTER Morrit., Assistant to the
Grain Future Trading Act see Secretary.
Oyice Of the-Noherterss R. W. WrittaMs, Solicitor.

This bulletin is a contribution from—

PALE CEL: Of CRENUISUT AY. — — = ee W. G. CAMPBELL, Acting Chief.
Miscellaneous Division__________-_-___- J. K. Haywoop, Chief.
27

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