HAWAII AGRICULTURAL EXPERIMENT STATION
Under the supervision of the
UNITED STATES DEPARTMENT OF AGRICULTURE
BULLETIN No. 50
THE SWEET POTATO IN HAWAII
H. L. CIHUNG, Specialist in Tropical Agronomy
Issued October, 1923
GOVERNMENT PRINTING OFFICE
,. j.r.;..3.. ..
HAWAII AGRICULTURAL EXPERIMENT STATION, HONOLULU.
[Under the supervision of the Office of Experiment Stations, United States Department or Agricuiltre V
E. W. ALLEN, Chief, Office of Experiment Stations.
WALTER H. EVANS, Chief, Division of Insular Stations, Office of Experiment Stations. .
J. M. WESTGATE, Aqronomnist in Charge.
H. L. CHUNG, Specialist in Tropical Agronomy.
W. T. POPE, Horticulturist. Ti
J. C. RIPPERTON, Chemist. *:
R. A. GOFF, In Charge of Glenwood Substation and Extension Agent for Island of HagulfE...
NELLIE A. RUSSELL, Collaborator in Home Economics.
MABEL GREEN, Boys' and Girls' Club Leader.
THE SWEET POTATO IN HAWAII.
By H. L. CHUNG, Specialist in Tropical Agronomy.
Introduction............... ............... 1 Cost of production................ ......... 10
Botanical relationship ......... ........... 2 Insact enemies and methods of control....... 11
Cultivation in ancient times................. 2 Fungus diseases and means of controlling
Place in the Hawaiian cropping system...... 2 them..................................... 13
Adaptation to Hawaii....................... 2 Varieties of sweet potatoes in Hawaii........ 15
Soil..................................... 3 Composition of the sweet potato............. 15
Methods of culture ........................ 4 Recipes..................................... 16
Grading.................................... 9 Sweet potatoes as feed for farm animals...... 19
Storing..................................... 10 Summary .......... .... ................. 19
It can not be definitely determined when the sweet potato (Ipomaea
batatas) was first cultivated in Hawaii, but it is thought that the
crop has been under cultivation on the island since about 500 A. D.,3
because the taro, which is a companion crop of the sweet potato, has,
from the earliest days, constituted the staple food crop of the natives.
Captain Cook records the finding in 1778 of specimens of taro of
large size, and sweet potatoes, weighing 12 to 14 pounds, in the
Hawaiian Islands, then known as the Sandwich Islands.
The sweet potato first became of commercial importance to the
Islands in about 1849. It ranked tenth in value of the agricultural
crops in 1919, having been reintroduced as an emergency crop.
The World War was an efficient factor in emphasizing the need of
producing locally grown food crops to make the island independent
of imported foodstuffs; and during this period the sweet potato was
used in place of potatoes, occasionally instead of barley and oats
for farm animals and for wheat and corn for poultry, and as a partial
substitute for wheat flour in the making of bread and pastries.
The crop is no longer exported, owing to rigorous quarantine regu-
Today the sweet potato is found growing in back yards and school
gardens and on areas covering upward of 50 acres on large ranches
throughout the islands. Fully 350 acres, located principally on
the islands of 4Hawaii and Maui, are now under cultivation. This
crop will undoubtedly play an important role in the further de-
velopment of the diversified agricultural industries of the islands,
more especially since it affords large returns in money from small
' The writer desires to express his appreciation to those in charge of the Bishop Museum, Honolulu,
for their courtesy in placing at his disposal information relative to ancient methods of cultivating the sweet
potato in Hawaii, and also to F. G. Krauss former superintendent of the Haiku substation, who very
kindly contributed data obtained at that substation.
* Alexander, W. D. A Brief History of the Hawaiian People, p. 19.
2 BULLETIN 50, HAWAII EXPERIMENT STATION.
The sweet potato belongs to the morning-glory family (Convolva ':
laceae) and is known botanically as Ipoma batatats. It is probably
indigenous to the West Indies or Central America. In the Tropics .
this plant is a perennial and produces long trailing stems. Except
in case of a few varieties, the sweet potato blooms profusely n i
Hawaii from November to April. The shape of the leaves and the.
color of the skin and flesh differ with the variety. The skin ranges
from white to dark brown in color, and the flesh varies from white
to pumpkin and dark purple.
CULTIVATION IN ANCIENT TIMES.
The sweet potato was grown with care by the ancient Hawaiians.
The vines for planting were not gathered at random, but with a
discrimination which showed that the native agriculturists ap- :
preciated the importance of selection. Vines of individual plants"
bearing roots in large quantities were selected for further planting.
PLACE IN THE HAWAIIAN CROPPING SYSTEM.
From ancient times the native Hawaiian farmer has realized the
advisability of alternating his sweet potatoes with other cultivated
crops to improve the physical condition of the soil. Observation
taught him that land which was allowed to rest for a year or so after
having produced a sweet-potato crop yielded a better and heavier
crop than did ground which was kept continuously in one crop.
Weeds and native grasses were therefore allowed to grow for a reason-
able length of time before the land was replanted to sweet potatoes.
The rice planters of to-day use the sweet potato and other cultivated
crops in their system of rotation. As soon as the last annual grain
crop has been harvested, the coarse straw is burned and the stubble
is turned under and harrowed. The land is then given a heavy appli-
cation of manure and is immediately used for some quick-growing
vegetable, such as lettuce, spinach, beets, radish, or mustard cabbage,
followed by sweet potatoes.
The following cropping systems are recommended for use in con-
nection with sweet-potato cultivation in Hawaii:
Two-year rotation.-Corn, cowpeas, sweet potatoes, peanuts; or. F
sweet potatoes, beans, buckwheat, cowpeas, and corn. i
Three-year rotation.-Corn, peanuts, grass or sorghums, cowpeas,
and sweet potatoes.
Four-year rotation.-Corn, mungo beans, sorghum, alfalfa, and
Five-year rotation.-Corn, peanuts, sorghum, pigeon peas, sweet
potatoes; or cassava, cowpeas, peanuts, sweet potatoes, and alfalfa,
ADAPTATION TO HAWAII.
Hawaii, being situated well within the Tropics, is naturally adapted
to the growing of sweet potatoes. The situation is so favorable, in
fact, that the plant produces immense roots, even when it is grown
in the pockets of volcanic rocks where there is little soil. The sweet
potato can be grown on all the areas of Hawaii except in rocky
THE SWEET POTATO IN HAWAII.
regions where there is no soil, in locations where there is an insuffi-
cient amount of rainfall, or on high elevations which are exposed to
The plant thrives from sea level to an elevation of 2,000 feet.
Growth can be maintained at a still higher altitude, provided the
location is sheltered from strong winds, which are decidedly harmful
to the plants. When grown at an altitude higher than 1,500 feet,
the period of maturity of a given variety varies with the altitude;
that is, the higher the elevation, the longer will be the period required
to mature the crop, owing to lower temperatures.
To make its best development, the crop needs moderate rainfall,
an abundance of sunshine, and warm nights from the time of plant-
ing until the vines produce vigorous axillary buds.
To produce its maximum yield, the sweet-potato crop should be
grown in a well-drained, moderately fertile, loose sandy soil. The
following hints may be of value to planters living in regions where
there is no soil of this kind.
Heavy clay soil.-When the sweet potato is grown in heavy clay
soil, such as local taro soil, it develops a dwarfed and sickly vine
growth and coarse roots which are likely to be unmarketable, owing
to their irregular shape. (PI. I.) Clayey soil renders aeration impos-
sible, since it is extremely sticky during wet periods and closely com-
pacted during the hot summer months, when it dries out in hard
To improve the physical condition of such soil, leguminous crops,
such as cowpeas and velvet beans, should be grown and plowed
under as green manure. The plowing under of leguminous crops adds
large quantities of nitrogen to the soil. Preparatory to the planting
of a second leguminous crop, and before harrowing is done, other
organic matter, such as rotted stable manure, rice hulls, or chaff,
should be broadcasted on the plowed field. Rice hulls can be obtained
from any rice-milling establishment in Hawaii for the asking and
cartage. The incorporation of organic matter in the clayey soil
loosens and mellows the soil and enables it to retain sufficient moisture
for plant growth.
Soils rich in humus.-The vines make luxuriant growth at the
expense of the roots when the crop is grown on land containing very
large quantities of humus. Such land should not be planted to sweet
potatoes for six months following the successive planting of crops
having edible foliage, such as green mustard, white mustard, and
Soils in seashore areas.-The sweet potato can be grown very
successfully on areas not far from the seashore and on soil containing
a large quantity of sand. Flat cultivation rather than ridge planting
should be practiced on such land, and organic matter and commercial
fertilizers should be incorporated with the soil from time to time
to render it productive. Only those varieties of sweet potatoes
which have already been acclimated and are adapted to seashore
conditions should be planted on sandy soil, otherwise the roots will
contain a high percentage of salt. Experiments conducted at the
experiment station on land near the seashore showed that the roots
4 BULLETIN 50, HAWAII EXPERIMENT STATION.
of four varieties of sweet potatoes contained from four to. svei :
times as much salt as did those grown at the central station. .i
In Hawaii, where there is an -uneven distribution of rainfall as
well as great diversity of soil types, the moisture content of the
different soils'varies considerably. Some of the soils are so porous
that the water filters through the surface instead of being absorbed,
and washes away much vegetable matter. Such soils may be imr -
proved in water-holding capacity by green manuring. Other soils
are too retentive of moisture and for this reason are detrimental to -
the crop. The sweet-potato crop should not be planted until it'l
known what the soil and rainfall conditions are.3
Virgin lands, or fields that have lain fallow for some time, should
be plowed and all volunteer growth turned under to insure excellent
soil conditions for the development of the roots of the new crop. If
the soil contains a suitable amount of moisture the roots will develop
near the surface, but if it is dry they will grow downward before
enlarging. Roots growing in a dry soil are difficult to harvest.
In localities where the fields are flooded after a heavy rain and the
water remains standing in the furrows for several days, not only are
the fertilizers leached out of the ridges, but the growth of vines is
stimulated at the expense of the roots. All the furrows should
therefore lead into a' channel at the lowest part of the field. After
the standing water has been removed from the furrows, the ridges
should be examined. On those which are saturated with water the
vines should be thrown to one side, so that the wind and sun will
hasten evaporation. After about four days, when these ridges have
returned to normal conditions, the vines should be thrown to the
opposite side, so that the newly exposed part will dry out. (Pl.
II, fig. 1.)
METHODS OF CULTURE.
Sweet potatoes are propagated either from vine cuttings or from
slips resulting from the sprouting of shoots from the root. In
Hawaii terminal cuttings are used almost exclusively, because they
have the ability to make quick growth and the advantage of being
practically free from insect pests. Old stem cuttings are likely to
carry the eggs or larva of the stem borer and are often the means of
infesting new fields with the pest. So far as resulting yield is con-
cerned, no appreciable difference has been found between the ter
minal and old stem cuttings.
In Hawaii, where propagating material can be readily taken from
the vine at any time of the year, the roots of the sweet potato are
not usually bedded in the greenhouse in spring for slips. It is only
when a variety shows signs of degeneracy, in the form of unproduc-
tiveness, that the sweet-potato roots are sprouted. The terminal
cuttings are removed in lengths of from 12 to 16 inches, and the large
leaves and their petioles are stripped from them. The cuttings
should be moistened and protected from drying when they are not
to be planted immediately after their removal from the vine. Fresh- j
* Planters may obtain a report on their soils by consulting the experiment station.
THE SWEET POTATO IN HAWAII.
cut vines which are planted in beds without irrigation make quicker
growth than do partly shriveled cuttings which are several days old.
Slips that are not to be planted immediately should be covered with
burlap bags saturated with water.
PREPARATION OF THE LAND.
The sweet-potato crop, like most other vegetable crops, gives best
results when it is planted on well-prepared land, especially on land
that has been planted with some leguminous crop the year preceding.
The area should first be thoroughly cleared of all coarse material and
then plowed fairly deep, the sod and debris being turned under.
The depth of plowing is an important factor in the preparation of
land and exerts considerable influence upon the character of the roots.
The depth used for corn will do for sweet potatoes. The fertilizer,
if any is to be applied, should then be spread broadcast, and the field
harrowed three or four times to make the soil sufficiently mellow.
Later a plank drag may be used to smooth the surface.
A spading fork is recommended for use in small areas. This im-
plement is very efficient for soils that are not compact and hard, as
the prongs strike well into the ground. Small areas which are
covered with low-growing weeds and other vegetation may be turned
under with it. Fertilizers should then be applied and a rake used to
level the area and to mix the fertilizer with the soil. Planting, either
by the level or ridge method, may begin a week later, when the
soil has had ample time to settle.
Three methods of planting are practiced in Hawaii, namely, (1)
ridge planting, (2) flat planting, and (3) individual mound or hill
Ridge planting.-This method is commonly practiced by the
sweet-potato growers of the islands, and is of advantage in that it
provides drainage, insures aeration, and puts the soil in good physi-
cal condition for the best development of the roots. The.ridges are
constructed of loose earth and vegetable matter and stand from 12
to 16 inches high. They are spaced about 3 or 4 feet apart and are
planted with 1 or 2 cuttings set I and 2 feet apart in the row. (P1.
Soils which are located near the seashore should not be ridged, be-
cause ridging tends to increase the surface area and to hasten evapora-
tion of soil moisture.
Flat planting.-This method of planting is also extensively prac-
ticed, but more especially on very sandy loam or sandy soil. In
flat planting the surface of the soil is made flat or level before planting
Mound or hill planting.-The method of setting plants in hills or
elevations of earth (P1. III, fig. 1) has been handed down from
primitive times and has an advantage over the other two methods,
so far as the native Hawaiians are concerned, in that it permits
of the mound's being broken down and the roots exposed at once with-
out great effort. The natives make it a rule to harvest only enough
roots to cover the needs of the day. The mounds are from 9 to 12
inches high and are spaced about 24 inches apart each way.
6 BULLETIN 50, HAWAII EXPERIMENT' STATION.
The number of sweet-potato cuttings required per acre is
in the following table: it
Number of sweet-potato cuttings required per acre .when planted at different da. ihw'
The sweet potato requires careful cultivation when it is grow 1 i
soil other than sand or sandy loam. The shape and size of the roo
are materially affected by the physical condition of the soil. Cultiva-
tion loosens and aerates the soil, and puts the plant food in such
condition that it can readily be assimilated by the crop. It also keeps
down weed growth and helps to conserve soil moisture.
The first cultivation should be given when the vines are a6ti6
8 inches long, or sooner, if the field is weedy. Cultivation consistW
in turning under the weeds and throwing the soil from the furrow .t
the ridge with a small one-horse plow, supplemented with hoeinga
to bring the soil up around the plant. When the vines are grown
under level cultivation, a harrow should be used on the soil. Usually
three or four cultivations are sufficient to keep the soil in good tilth
until the field is overrun with vines. Weed growth is promoted dal-
ing the rainy season, and the ground then requires frequent cultiv4'
tion. Sweet potatoes can best be cultivated with a hoe when they
are grown on small areas.
The sweet potato readily responds to applications of fertilizer. At
the experiment station an increase of 42 per cent in yield resulted
from the application of a mixture of sodium nitrate, potassium
sulphate, and acid phosphate, in the proportions of 75, 150, and 400
pounds, respectively, per acre. At the substation at Haiku, Maui,
sodium nitrate, potassium sulphate, and equal parts of reverted
phosphate and acid phosphate, in the proportions of 100,150, and 250
pounds, respectively, per acre gave the best results.
It is suggested that the potassium sulphate be increased in the
first formula to 200 pounds for very sandy soil, half of the fertilizer
being applied when the plants have been set for about five weeks;
and the rest five weeks later. The fertilizer should be uniformly
applied. The Haiku formula is recommended for use on areas where
the soil is adapted to the production of sweet potatoes, but on elevated
regions maturity is delayed by reason of the altitude, the reverted
phosphate being gradually made available to the plants during the
protracted period of growth. 14
Distance Distance Number of Distance Distance Number of
apart of apart in sweet-potato apart apartin p to
rows. rows. g rows. rows. c
per acre. per acre.
Feet. Feet. Feet. Feet.
2 2 10,890 3 3 4,840
2i 2 600o8 3j 1 8,207
3 1 9,680 4 2 5,445
3 2 7.260
Bul. 50. Hawaii Agr. Expt. Station.
PRODUCED IN HEAVY CLAY SOIL.
IRREGULAR IN SHAPE
Bul. 50, Hawaii Agr. Expt. Station.
FIG. I.-VINES TURNED TO ONE SIDE TO PROMOTE EVAPORATION FROM
SOIL OF EXCESSIVE MOISTURE CAUSED BY STANDING WATER.
FIG. 2.-SWEET POTATOES GROWN BY RIDGE METHOD.
PLATE I I :
THE SWEET POTATO IN HAWAII.
g action is not an important consideration ii connection with
hS etpotato growing in .Hawaii owing to seasonal conditions and
di4ought-resistant character of the plant. It thrives and pro-
4 ices a crop of roots with very little moisture. The type of soil and
I he amount of rainfall largely determine where and when the crop
i. aan" be grown to the best advantage. When rainfall is the only
source of moisture, the crop should be frequently cultivated to con-
serve moisture as the dry season approaches.
The plants should be watered sparingly when they are grown on
irnall areas or in localities where irrigation is possible. It is impos-
sible to establish a definite rule for time of irrigation, because some
soils retain moisture longer than do others, but it is good practice to
water the plants when the soil, to a depth of 3 or more inches, is
comparatively dry to the touch.
A very effective way of irrigating the sweet-potato crop is by
turning the water into alternate furrows. This practice permits
thorough saturation of the soil immediately surrounding the plant
and precludes the possibility of its packing later. In flat culture
light irrigation, rather than heavy, should be practiced.
Some of the local growers cut the sweet-potato tops from the
cultivated field for feeding hogs. To determine the effect of such a
practice upon yield of roots the experiment station, in 1917, carried
on a test, covering eight months, with the Yellow Yam variety of
sweet potato. The plants were set in 12 rows, each 100 feet long,
and the vines were cut once a week after they had attained a length
of 18 inches. The following table gives the result of the test:
Efect on yield of cutting back sweet-potato vines.
Length to Calculated
Rows. which vines
were cut. acre yield.
1i 3, 4...... .... ............... ...................... .......... ......... 12 6,859.4
6, 7, .................. .................................... ............ (1) 21, 857.6
10, 11, 12 .................................. ......................... 18 10 779.1
1 Not pruned.
The above table shows that the yield of sweet potatoes is greatly
decreased when the vines are cut back. The rows, the vines of which
were kept within 12 to 18 inches long, produced a yield of roots
approximating 31 and 49 per cent, respectively, of a crop as compared
With the unpruned vines. The test showed that many pruned vines
were devoid of enlarged marketable roots. Apparently the shorter
the vine is cut, the greater will be the reduction in yield.
The period of maturity of the sweet potato differs with the variety
and the locality in which it is grown. Some varieties mature a crop
much earlier than do others. In all varieties the period required for
8 BULLETIN 50, HAWAII EXPERIMENT STATION.
maturity is lengthened when the crop is grown at the higher,
tions. Sweet potatoes are classified in three groups, those ma
in three months, or early varieties; those maturing between Y
and five months, or medium early varieties; and those ma
between six and seven months, or late-maturing varieties.
suppose that the crop is mature and ready for harvesting in
four or five months after planting if the leaves turn yellow. Ye -
ing of the leaves is not always an indication of ripening and may h
caused by drought or the disease known as stem rot. Excepsijr
rainfall, on the other hand, stimulates the growth of the' vines ai
causes the foliage to remain green for months after the roots have
matured. Again, it is supposed that the crop has matured if the
roots remain white upon being broken, and that, vice versa, immaturi-
ity is shown by discoloration of the broken surface. In experienpfa
with sweet potatoes which were known to be immature, te e xpi-
ment station found no discoloration to occur after breaking except
that due to the milky substance, latex, which is also present in tme
On account of its excellent keeping qualities the sweet potato iii
Hawaii may be left unharvested in the field for months without like- :|
lihood of its decaying, even when the period of maturity has passed. '
If the roots are kept in the ground after maturity, not only will the-
quality be improved materially, but the yield will be considerably
increased. The question of when to harvest, then, is not an impor-
tant one, so far as maturity is concerned. Under no circumstances,
however, should the crop. be harvested after a rain when the grotxiu
is very moist, if the roots are intended for market and a large area
is to be harvested. When the soil is wet, sweet potatoes are difficult
to harvest and the earth sticks to them.
A gardener whose sweet-potato area is small may harvest his
crop before it matures fully. To harvest the required quantity of
roots without disturbing every hill, the vine should be carefully
lifted and the ground examined for large cracks or crevices around
the plant. These cracks are found when the soil surface is dry and
occur where extra-sized roots are growing.
In small areas, and where the crop is grown primarily for home
consumption, harvesting may be facilitated by means of a four-
pronged spading fork. After the vines are removed the fork should
be inserted in the soil at a distance of 8 or 10 inches from the plant
and the roots lifted and brought to the surface.
When the crop is grown on a large scale in Hawaii, a turnplow is
used for harvesting after the vines have been removed by hand.
The sweet potatoes are brought to the surface' by plowing, thrown
to one side by men, and later are graded for market. The roots
should be left in the field and exposed to the sun for a few hours to dry
The yield of sweet potatoes depends largely upon the locality and
soil in which the crop is grown, the kind and amount of fertilizer
used, the culture given, and finally upon the variety itself. A yield
of 10 tons per acre can be secured from a crop that is grown under
favorable conditions. As high a yield as 171 tons of roots and
214 tons of vines per acre has been produced at the Haiku sub-
THE SWEET POTATO IN HAWAII.
station. If the yield is estimated on a small basis, 100 plants,
spaced 4 by 2 feet apart, should produce at least 150 pounds of
merchantable and 50 pounds of cull roots.
In varietal tests covering a period of five years at the central station
at Honolulu an average yield of 4 tons per acre was obtained from
all the varieties tested. In these tests the early maturing varieties
were less productive than either the medium or late varieties. The
following table gives the comparative yield of a number of these
Comparative yield of sweet potatoes tested at the central station.
Variety. Yield Variety.Yield
per acre. per acre.
Delicious ............................ 3.7 Native Red. ....- ...-.......... ....... 6.0
Huamoa ............................. 4.1 "Yellow Yam"....................... 6.6
Pikonui.............................. 3.2 New Era............................ .. 6.7
No. 111-A............................. 3. 1 Tantalus.............................. 6.2
Madeira ............................... 5.4
The yield of sweet potatoes may be increased by proper culture
and the application of fertilizers, or by the selection through several
generations of individual hills producing heavy crops of desirable
and well-shaped roots. The most opportune time to select for
improvement is when the crop is being harvested. Hills are then
dug individually, showing numbers of roots of varying shape and
size. Vine cuttings should be taken from the hills which contain
the largest number of roots of good size and uniform shape (P1. III,
fig. 2). These should be carefully labeled and notes made concerning
their individual parents.
Many hills should be selected for foundation work, because some
of them will fail to transmit their prolific characteristics. Improve-
ment should then be continued by eliminating the unproductive
vines and retaining those bearing heavy crops of roots. (Pl. IV,
fig. 1.) Within a period of five or six years, representing 10 or
more generations, the grower will be able to establish a prolific strain
of fine quality which he is entitled to call his own and to give a special
name if its characters are sufficiently distinct.
Although sweet-potato grading has been advocated in Hawaii for
many years, wholesalers continue to purchase solely on the basis
of exchange of so much money for so much weight, regardless of
kind of material weighed. The local farmers raising diversified
crops recognize the importance of standardizing agricultural produce
as a means of building up their business, but the local growers, who
supply the markets with sweet potatoes for culinary purposes, are
indifferent to suggestions regarding grading, either because the planting
of this crop is incidental to their specialized crops and the area is so
small that it does not justify the extra labor expended in grading,
or they have learned that quotations are the same for graded and
ungraded sweet potatoes. Standardization of the crop will not
become a reality until uniformity of size, shape, and color enters into
10 BULLETIN 50, HAWAII EXPERIMENT STATION.
the transaction and sweet potatoes arex markbtied padS.
from cuts, bruises, decay, scars, cracks, and other defects
from careless handling, as well as from diseases and insect
SELECTION OF SWEET POTATOES FOR HOME USE.
Fully 15 to 25 per cent of the total weight, depending up
shape of the roots, is lost in the paring of sweet potatoes w
intended for culinary use. In other words, there is removed t
form of paring from 1i to 2 pounds by weight for every 10 wp
of sweet potatoes pared. For this reason there should be sele
for home use regular-shaped, uniform, smooth, firm, and fr
looking roots rather than shriveled or irregular-shaped specimens".'lii
In Hawaii the sweet potato is not stored for future use for
great length of time, because the crop can be harvested during
month of the year. After sunning for a few hours in the field !
roots are taken to a shed and spread out in shallow piles to c'ri4
thoroughly. A number of sweet-potato growers on Oahu make it :.
practice to harvest just enough to supply the current needs of ite ::'
wholesaler, and the native Hawaiians never harvest more .thAin: .,tlim:
actual quantity of roots needed to supply the household for thedaa ,
In this they show an appreciation of the quality of the freshly dit
root and a knowledge of how to eliminate the problem ofsto. iqg
The small gardener would do well to adopt their practice.
: .. -: *
SHRINKAGE IN STORAGE.
Data obtained at the experiment station on shrinkage occur
in sweet potatoes, which are sacked and left in a cool but dry rio,
show that a loss of 12 per cent of the original total weight t4kas
place in 21 days, approximately 6 per cent of which is lost during t i
seven days immediately following harvesting and 6 per cent during
the next 14 days. It is evident, therefore, that sweet potatoes should
be carefully stored to reduce the loss by shrinkage to a minim in ,
Storage houses intended for sweet potatoes should have wood '
roofing, which does not have the same heat-retaining properties at
does galvanized-iron roofing, and the storage rooms should be kept
cool and dark.
COST OF PRODUCTION.
The cost of producing a crop of sweet potatoes depends largely upon
the locality where it is grown and the method of growing. On level
land, where labor-saving devices can be used to do considerable of
the work, the cost per acre is less than is the case on hilly lands wherp
the greater part of the work has to be done by manual labor. IS;
Hawaii, where labor is rated as an expensive item, the cost of .-
ducing an acre of sweet potatoes ranges between $80 and $1Q
exclusive of the charge for rental of land, fertilizers, and coa0 :
sacks. The following table gives the comparative cost of prqdua-
sweet potatoes at the central station, the substation at Haiku, n ;
on the mainland: :. .
Bul. 50, Hawaii Agr. Expt. Station.
FIG. I.-SWEET POTATOES GROWN BY MOUND OR HILL METHOD.
FIG. 2.-CLUSTER OF SWEET POTATOES OF UNIFORM SIZE AND SHAPE.
Bul. 50, Hawaii Agr. Expt. Station.
FIG. I.-HILLS BEARING
SWEET POTATOES IN GOOD CLUSTERS.
MADE FROM PLANTS OF THIS TYPE.
FIG. 2.-SWEET POTATOES BADLY DAMAGED BY STEM BORERS.
.. : E
SI1 2 1I
... ; ..
. '' *:
THE SWEET POTATO IN HAWAII.
SCeompion of the cost of producing sweet potatoes in Hawaii and on the mainland.'
Central Haiku sub-
S station. I station.
S Plow g (3 times).-.............................................. $18:00 $8.00 $15.00
..... ......................... .......................... 6.00 5.00 4.00.. .
a-...........- .......................................... 315.00 15. 00 10.00...........
.i ........ ..........................................8.. 61.00 ............
r .. ................. ....... ....... .......................... .00oo .00 4.00
............................................................ 1 .00 i 5.00 10.00
S........................................................... 8.00 6.50 5.00
t ation ........................................................ 6.00 4.50 5.00
ing vines ..... ............................................. 29.00 ............
g......................................................... 16.00 15.00 25.00
p 1 j cost, due to experimental data obtained...................... 10.00 ...... .. ...........
g............................................................ 5.00 o7.50
104.00 90.50 61.00
SSee Farmers' Bul. 324, Sweet Potatoes, p. 38.
s The item of cost in removing the vines is recovered by disposing of the vines as a soiling crop. They
were delivered to the piggery of the Haiku substation for $5 a ton.
The above table shows that the cost of production at the experi-
pent station was considerably more than was the case at either the
Haiku substation or on the mainland. This difference was largely
due to the great care which was exercised in the planting, cultivation,
and weighing of the roots and vines, grown as they were under experi-
mental conditions rather than under ordinary field conditions.
The figures of the Haiku substation serve as representative items
in the cost of production when the crop is grown on a commercial
basis in Hawaii. At this substation the cost per cultivation was
$1.50, or three cultivations for $4.50; the cost of removing the vines
and loading them on to the wagon was at the rate of $1.50 per ton,
or 6 tons for $9. An item of 15 cents represents the actual cost of
preparing, harvesting, cleaning, grading, and sacking a 100-pound
- sack of sweet potatoes for delivery from the field. On the basis of
100 sacks per acre the cost would be $15, as indicated. The hauling
charge was $1.50 per ton.
The mainland cost for producing an acre of sweet potatoes is decid-
edly low, as shown by the table. The use of labor-saving devices and
the growing of the crop in extensive areas make the low figures
possible. The item of $15 for three plowings also includes the cost
of disking and leveling the surface prior to ridging, and the item of $25
for harvesting, includes cost of cleaning,-grading, sacking, and
INSECT ENEMIES AND METHODS OF CONTROL.
The sweet potato in Hawaii is attacked by a number of insects
which feed upon the leaves, stems, and roots. Leaf-eating insects
cause little permanent injury to the plant, owing to its vigorous
growth, and they can be brought under control with proper measures.
Practically all of the insects-attacking the crop have been described
in Bulletin 22 of this station, and only those which are especially
injurious are mentioned here.
12 BULLETIN 50, HAWAII EXPERIMENT STATION.
INSECTS INJURING THE OLIAGE.
JAPANESE BEETLE (Adorettu tenuimaculatus).
The Japanese beetle perforates the foliage of the sweet-po ...
plant. The pest can be brought under control by spraying the
side of the foliage with a mixture containing 1 pound of lead a
in 20 gallons of water. ,
SWEET-POTATO LEAP-MINER (Bedellia orchileJlla).
The leaf-miner, after the stem borer, is perhaps the most destit ;
insect enemy of the sweet-potato vine. Its injuries are confinqted
the foliage, which as a result presents a notched and withered appeal
ance and bears traces of excrement. The newly hatched -lar-:
penetrate the leaves and feed upon the green coloring matter. The
leaves gradually lose their color and wither, and the leafstalks drop: .
The leaf-miner can best be controlled by the removal and burning
of severely infested foliage and by the practice of clean cultivation.
SWEET-POTATO SPHINX (Herse convolvuli).
During the rainy season the sphinx caterpillar periodically appears
on sweet-potato vines. The eggs are usually laid on the under 4ide
of the leaves of the wild morning-glory Ipomwa digitata, and occasioa-
ally on those of the sweet potato. The caterpillar is from 2 to 6 inch
long, ranges from light green to dark brown in color, and is charac-
terized by a single black horn.
As a means of control, all host plants, such as morning-glory and
pigweed (Portulaca oleracea), should be destroyed. On vacant lots
in the Waialae district of Oahu wild morning-glory vines should be
destroyed to protect the surrounding fields of sweet potatoes from
attack by the sphinx caterpillar.
Spraying the under side of the leaves with arsenate of lead solution
(1 pound of the arsenate to 20 gallons of water) will materially reduce
the number of caterpillars. This pest may also be kept in check by
picking the larve from the vines growing on small areas.
SWEET-POTATO LEAF-ROLLER (Phlyctania despecta).
This leaf-roller is one of the minor insect pests attacking the foliage
of the sweet-potato crop. In extreme cases it skeletonizes the leaves
and envelopes the remaining structure in a filmy web. The young
caterpillar, although colorless, usually appears green, owing to the
green contents of the alimentary tract, which can be seen through
the body. Its hiding place is on the under side of the leaves.
An application of lead arsenate to the leaves is recommended as a
control measure. Clean cultivation should also be practiced.
INSECTS INJURING THE STEM.
CUTWORM (Agrotis ypsilon).
Cutworms attack the sweet-potato vine at night during the early J
growing period, eating the terminal and axillary buds and sometimes
completely cutting off the growing vine at the base.
As a control measure the use of poison bait, composed of 1 pound
of molasses, I pound of lead arsenate, and 10 pounds of bran,
thoroughly mixed and spread near the base of the vines, is recom-.
STHE SWEET POTATO IN HAWAII. 13
i mended. If the soil around the base of the plant is stirred with a
small stick, the worms will leave their hiding places and can then be
INSECTS INJURING THE ROOTS.
SSWEET-POTATO WEEVILS (Cryptorhynchus batata and Cylasformicarius).
Sweet-potato weevils are quite destructive at times, thoroughly
channeling the roots with larval burrows and causing the vines to
shrivel and decay.
As a control measure, all infested potatoes and trash above ground
Should be burned and clean cultivation should be practiced.
INSECTS INJURING BOTH STEM AND ROOT.
STEM BORER (Omphisa anastomosalis).
The stem borer is perhaps the most destructive of all the insects
attacking the sweet potato in Hawaii. It not only burrows large and
distinct tunnels in the stems of the plant, but also damages the root
crop. (P1. IV, fig. 2.) In a severely infested field the vines die and
the yield of roots is greatly reduced.
Stomach poisons are of little avail in connection with the stem
borer, as most of its life is passed within the stem or the roots. Prob-
ably the most effective way of combating it is by the practice of clean
cultivation. All infected vines and roots should be gathered and
burned. In severely infested small areas the borers can be crushed
within the stem by the pressure of the fingers up and down the
FUNGUS DISEASES AND MEANS OF CONTROLLING THEM.
The sweet-potato plant is attacked by a number of diseases which
are divided into two classes: (1) Those attacking the crop in the
field, and (2) those attacking the crop in storage.
DISEASES ATTACKING THE CROP IN THE FIELD.
BLACK ROT (Spheronema fimbriatum).
Black rot, due to the fungus S. fimbriatum, is not confined to the
field, but also attacks the crop in storage. Infected roots, when
taken from the field, show discoloration in small patches which enlarge
and finally affect the whole root. Cooked sweet potatoes which are
affected with black rot have a bitter taste.
STEM ROT (Fusarium batatatis).
Stem rot, caused by an organism (F. batatatis), commonly attacks
the plant and its roots. As the name indicates, the stem is affected,
usually becoming blackened in the advanced stage, and the foliage
turns a dull yellow and drops. As a rule the vine wilts, and in the
instances where it does survive the roots are discolored.
SCURF (Monilochltes infuscans).
Scurf, also known as soil stain, is due to a fungus (M. infuscans)
which adheres in such a way to the roots as to be mistaken for soil
particles. It is not a serious disease and damages the potato only by
BULLETIN 50, HAWAII EXPERIMENT STATION.
discoloring the skin. A white-skinned variety wheu t
presents a dark-gray appearance, while a red-skinned .Vri t h
black. :. I".IA
FOOT ROT (Plnodomus detruens).
Foot rot is indicated by rotting of the stem near the surface of tb ,:.,;.
soil. The infected plant presents a father wilted appearance..
BLIGHT or WILT (Sclerotium rolfsi).
Blight or wilt is indicated by decay of the plant at the base andA I :
moldy white growth. r
TEXAS ROOT ROT (Ozonium omnivorum).
Texas root rot is indicated by a spotting of the roots and a wilting
of the vine.
PIT OR Pox (Cytospora batatas).
Pit or pox, also known as soil rot, is indicated by malformation
and girdling of the roots of the plants, accompanied by low yield.
DISEASES ATTACKING THE CROP IN STORAGE. .i
Snr RTn'r ANTn RTNO RnT (Rhiz nnqL rninrirYnn\
'r, RO ADRN .Ry *Ri
Soft rot is indicated by decay of the root at one end, the diseaged
part becoming very soft.
Ring rot'is indicated by a softening of the roots between the ends.
DRY ROT (Diaporthe batatatis).
Dry rot is indicated by shriveling of the roots, unaccompanied by
JAVA ROOT ROT (Diplodia tubericola).
Java root rot is indicated by blackened flesh.
Three minor diseases which affect the foliage of the plant are leaf-
blight, giving the plant a withered appearance; leaf-spot, identified
by minute white specks on the leaves; and white-rust, indicated by
small white spots. Being only minor diseases, they require no treat-
ment when occurring on a large area. Infected leaves should be
removed from small areas, however, and burned.
It is only by the most careful management that sweet-potato
diseases can be eliminated from the field. The selection of prop-
agating materials from absolutely sound plants, the careful examinm-
tion of the root crops and vines before moving from one field to
another, and the practice of crop rotation are the only effective
Cuttings which are intended for propagation should be selected
with care if they are taken from infected areas. They should be
treated with a solution of bichlorid of mercury (1 ounce of bichlorid
of mercury to 8 gallons of water), being submerged in the solution' for
five minutes. Vines or roots showing signs of disease should be
removed from the field and burned. If a locality continues to be
THE SWEET POTATO IN HAWAII.
S infected, notwithstanding its receiving every precaution to make it
disease free, it should be allowed to lie fallow for a year or two and
then be planted with about 20 varieties of sweet potatoes. Selection
should then be made for future planting from the varieties appearing
healthy and producing luxuriant foliage and good crops of sound
VARIETIES OF SWEET POTATOES IN HAWAII.
Approximately 70 distinct varieties of sweet potatoes having
Hawaiian nqnes are known to the native growers, and fully 200
others are either unnamed or bear English names.4 Many of these
varieties are undoubtedly cultivated elsewhere under different names.
For practical and commercial purposes the following listed varieties
are recommended for table use and for feeding to live stock:
Varieties of sweet potatoes which are adaptedfor both human consumption and for live-
Varieties. Color of skin. Color of flesh.
Delicious Yellow............................................ Purplish pink..... Pumpkin.
Huamoa................................................... Straw............ Orange.
Pikonui ...... ................. ........................ ....do.....d ........ Light yellow.
Medium early maturing:
No. 111-A................................................... White............ White.
Madeira .........................................................do........ ... Light yellow.
Native Red ................................................. Red............... W white.
SYellow Yam "............................................. Straw............ Pumpkin.
New Era ................................................... Dark buff......... Light cream.
Tantalus .................................................... Light brown...... Cresm .
SMadeira..................................................... W hite............. Light yellow.
1 The late-maturing varieties are especially recommended for live-stock feeding because they are prolific
bearers, and good keepers, and contain a high percentage of starch.
A great variety of potatoes is needed in Hawaii to meet the demands
of the cosmopolitan population. The occidental population in
Hawaii prefers sweet potatoes having orange or pumpkin-colored
flesh, while the oriental population prefers a red-skinned variety
having flesh varying from white to canary in color.
COMPOSITION OF THE SWEET POTATO.
Sweet potatoes vary considerably in chemical composition ac-
cording to the variety and the place where they are grown. The
following table gives a comparison of the sweet potato with other
Relative value of the sweet potato and other starchy root crops.a
Crop. Water. Ash. proen hrats Fat.
Percent. Percent. Percent. Percent. Percent.
Sweet potato (whole)............................. 68.89 0.90 2.12 27.83 0.25
Sweet potato (peeled)............................. 68.50 .94 2.18 28.18 .2.3
Sweet potato (peeling).............................. 74.35 .31 1.29 21.96 1.09
Cassava (whole).................................... 64.17 .86 .77 32.61 1.59
Taro (whole)................................... 60.55 .73 1.10 37.49 .13
Potato (whole) b.................................... 78.30 1.00 2.20 18.50 .13
'Practically compiled from Hawaii Sta. Press Bul. 53.
a'Unpublished analysis made by the Hawaii Experiment Station.
4 Sweet-potato breeding has been carried on by the experiment station since 1917, since which time more
than 700 seedlings have been produced.
BULLETIN 50, HAWAII EXPERIMENT STATION.
From the above table it will be seen that the sweet-pot,4q9 1f:i:'
compares favorably in chemical composition with the thrill 1'$bN
root crops. The whole sweet potato shows a higher ash a.nd cte'I
protein content and a lower carbohydrate content than do~ns 0itir
the cassava or the taro. In fat content it is lower than the casalfky
but higher than the taro. A comparison of the sweet potato wi"th"
the potato brings out the significant fact that the former is about
as high in crude protein content as is the latter and that it is much
higher in carbohydrates and fat. Notwithstanding these facs, thw
potato commands the higher price of the two on the Dcal markets
throughout the year.
Sweet potatoes are prepared for table use by practically all of the
many nationalities in Hawaii, in the occidental homes and hotel
being baked, boiled, or braised, and in the oriental homes, boiled
whole, or pared, sliced, and then boiled. Starch is extracted from
the raw potato for the preparation of a paste-forming meal which
can be fed to infants and also to adults. Some of the methods 'o
using the sweet potato are given below.
cupful of mashed sweet potatoes.
teaspoonful of salt.
tablespoonful of sirup, if desired
tablespoonfuls of lukewarm water.
21 cupfuls or more of sifted flour.
j to I cake of yeast (dry or compressed),
or from 2 to 4 tablespoonfuls of liquid
Use left-over boiled or baked sweet potatoes or boil sweet potatoes in their jackets
until tender. Pare and mash the sweet potatoes or put them through a colander or
ricer to free them from lumps.
Short process.-To 1 cupful of the cool mashed sweet potatoes add 1 teaspoonful
of salt, 1 tablespoonful of sirup, and I cake of compressed yeast mixed with 4 table-
spoonfuls of lukewarm water, or 4 tablespoonfuls of liquid yeast. It may be necessary
to add more water if the sweet potatoes are rather dry or mealy. Add to this J to 1
cupful of sifted flour and stir until the whole is thoroughly mixed. Cover and allow
the mixture to rise for about two hours until it becomes soft and light. Knead in
another quantity of flour sufficient to make a dough somewhat stiffer than for whith
bread. Knead the mixture until it is smooth and elastic, then cover and let it rise
again until it becomes very light. Knead, mold, and finish as usual. Allow the mass
to rise in the pan until it reaches 2. or 3 times its original bulk. Bake slowly in a
moderately hot oven for at least 50 minutes.
Long process.-To 1 cupful of the cool mashed sweet potatoes add 1 teaspoonful of
salt and either cake of yeast, dry or compressed, mixed with 4 tablespoonfuls of
lukewarm water, or 2 tablespoonfuls of liquid yeast. Add to this J to 1 cupful of
sifted flour. Cover and set' to rise where the temperature ranges from 60 to 700 F.
When the mixture is light and soft add the sirup and knead in another quantity of
flour sufficient to form a smooth, elastic, and rather stiff dough. Cover and let rise a
second tim6 until it becomes very light. Then knead, mold, and finish as directed
for the short process.
Cooked or baked squash, pumpkin, peas, beans, or dasheen may be substituted for
sweet potatoes. When larger quantities of sweet potatoes are to be used, less water
will be required; that is, for every 1j cupfuls of mashed sweet potatoes only 2 table-
spoonfuls of water per loaf are needed. In this case less flour will be required.
2 cupfuls of sifted flour.
1 tablespoonful of salt.
3 teaspoonfuls of baking powder.
1 cupful of mashed sweet potatoes.
3 tablespoonfuls of shortening.
Sufficient water or milk to mix.
* Liquid yeast, when used, should be included in the total liquid.
THE SWEET POTATO IN HAWAII. 17
Sift the flour, salt, and baking powder together. Cut or rub the cold shortening
into this mixture. In the same way nib into this flour mixture the mashed potatoes.
Finally, add just enofigh cold liquid to make the mass cling together. Do not knead.
Place mass on floured board, roll until 4 inch thick, and cut with a biscuit cutter.
Place in lightly floured biscuit tins and bake for 15 or 20 minutes in a moderately
hot oven. Bake potato breads more slowly than all-flour breads.
The tops of the sweet potato vine make excellent greens for the table, comparing
in this respect with spinach. Remove the tips to a length of 3 inches, wash, and
place in saucepan containing water and salt. Boil, drain, and season with salt and
pepper before serving.
1 tablespoonful of sweet-potato starch. About 1 cupful of boiling water.
4 cupful of cold water. Sugar to sweeten.
Place the sweet-potato starch in a quart container, add water, and mix thoroughly.
Gradually add boiling water and stir until a thick, paste-like porridge is formed. Add
sugar to sweeten and serve.
Pare sweet potato, cut into slices about one-fourth inch thick, and place in a
saucepan containing barely enough water to cover. Cook over a moderate fire for 14
hours. A little sugar may be added if desired.
HAM SMOTHERED IN SWEET POTATOES.6
1 slice of smoked ham cut into sizes for 2 tablespoonfuls of sugar.
serving. 1 tablespoonful of butter or ham fryings.
3 cups of raw sliced sweet potatoes. 1 cupful of hot water.
Broil the pieces of ham lightly on both sides and arrange them to cover the bottom
of the baking dish. Spread the slices of sweet potato over them, sprinkle with sugar.
Add the hot water and extra fat. Cover the dish and bake slowly until the ham is
tender, basting the potatoes occasionally with the gravy. Brown the top well.
SWEET POTATOES AND PEANUTS.
1 quart of mashed sweet potatoes. teaspoonful of cinnamon.
2 tablespoonfuls of butter or other fat. 1 teaspoonful of salt.
1 cupful of roasted peanuts chopped fine.
Mix the ingredients well; form into a mound upon a shallow baking dish; press a
tablespoonful of butter into the top. Heat in a moderate oven until brown.
To 1 pint of boiled and mashed potatoes add 1 pint of toasted bread crumbs rolled
fine, I pint mixed nut meats chopped fine (peanuts are excellent); season with salt,
a little pepper, also sage and mace, if desired; to the yolks of 2 eggs add 2 teaspoons of
baking powder and whip until light; pour the egg mixture into the first-mentioned
mixture and stir well; form into small cakes; dip each into the whites of the eggs, then
into shredded coconut, and brown in a frying pan containing a little pork fat (not deep
fat); turn; brown on both sides.
This and the following recipe were obtained from miscellaneous sources through the courtesy of the
Bureau of Home Econonncs of the United States Department of Agriculture.
SThis and the following recipes were obtained from the Tuskegee Normal and Industrial Institute,
Tuskegee Institute, Ala., through the courtesy of Dr. G. W. Carver. (Bul. 38, How the Farmer Can Save
His Sweet Potatoes.)
BULLETIN 50, HAWAII EXPERIMENT STATION.
SWEET POTATOES WITH ROAST PORK.
Parboil the desired number of potatoes with the skin on until nearly &ui
and skin; put in the baking dish with the nearly done roast; cook until don, 4 Z l
with the pork.
Cut in thin slices, steam until nearly done, allow the surplus water to drain off, or
dry between napkins, fry in deep fat to a light brown. A little salt adds to its flavor.
SWEET POTATOES BAKED WITH APPLES.
Wash, pare, and cut 4 medium-sized sweet potatoes into slices about inch thick,
pare and slice 4 apples in the same way; put in baking dish in alternate layers; sprinkle
13 cups of sugar over the top, scatter j cup of butter in lumps over the top; add j pint
of hot water; bake slowly for 1 hour; serve steaming hot.
Whip 2 eggs until quite light; 2 cupfuls of cold mashed potatoes; 1 cupful of flour -
into which 1 teaspoonful of baking powder has been sifted. The potatoes and eggs
should be worked together, then the flour and baking powder; roll lightly; cut quickly,
and fry in deep fat like doughnuts. Some think a little spice improves the flavors
Boil in skins; when tender remove skins, mash and beat until light; to each pint add '
a pint of milk and 4 eggs. Season and bake as pumpkin pie.
Cut in slices J inch thick, wash, and place in deep saucepan spread with butter,
season with a little grated nutmeg and salt; moisten with broth or water, cover and let -.
simmer over slow fire for j hour, turning the slices so that they may glaze on both sides.
Serve with drawn butter or other sauce.
SWEET POTATOES STUFFED.
Bake; then cut off one end and scoop out the inside; season with butter, pepper, and
salt; beat until light; replace in the skin; close with the piece cut off and put into the
oven to heat through. Serve in napkins. Suitable for luncheon.
A SOUTHERN DISH.
Cut cold baked sweet potatoes into slices and put into an earthern dish; add sugar
and butter to each layer and bake until slightly browned.
Take 2 cupfuls of mashed, boiled, steamed, or baked sweet potatoes; add the beaten
yolks of 2 eggs and season to taste; stir over the fire until the mass parts from the sides
of the pan. When cold form into small croquettes, roll in egg and bread crumbs, and
fry in hot lard to an amber color. Serve on napkins. The croquette mixture may be
made into balls inclosing minced meat. When used in this way, serve with sauce.
Mash boiled, steamed, or baked sweet potatoes, season, and add enough hot milk to
moisten; serve like mashed white potato; or put in pudding dish, dress the top with
egg, and brown in the oven. Serve with sauce.
SWEET POTATOES BAKED.
Bake like potatoes, without breaking the skin. When done, break the skin in one
place in the form of a cross, forcing the meat partly out, cap with butter, and serve.
I This and the following recipes have been taken from United States Department of Agriculture Farmeri'
Bul. 129, Sweet Potatoes.
THE SWEET POTATO IN HAWAII.
SWEET POTATOES AS FEED FOR FARM ANIMALS.
When the sweet potato is grown on a large scale in rotation with
other crops and it is desired to economize on labor in harvesting the
roots, cattle and sheep may be pastured on the area to consume the
vines, and later hogs may be turned in to harvest the roots for them-
selves. If the area in sweet potatoes is exceptionally large, and the
above system of harvesting is practiced, the grazing area should be
inclosed with a portable fence to prevent waste when the hogs are
turned in to root. Potatoes which are brought to the surface but
not eaten should be daily gathered from the paddocked area and fed
to other hogs.
Sweet potatoes can be fed to horses and mules as a supplement to
the regular carbohydrate feed. The roots should be cut into pieces
with a vegetable cutter and then mixed with a small quantity of mo-
lasses, so that the animals will become accustomed to them. The
work mules at the experiment station are given rolled barley in the
morning, corn at noon, and chopped sweet potatoes in the evening,
when corn and sweet potatoes are available, This ration keeps them
in excellent condition.
Sweet potato tops.-In the hog-raising and dairy enterprises in
Hawaii large quantities of the succulent garden pigweed or purslane
(Portulaca oleracea) and honohono (Com melina nudiflora) are fed to
hogs and cows. The following table gives the chemical composition
of sweet-potato vines, pigweed, and honohono:
Composition of sweet-potato vines, pigweed, and honohono.
Crop. Water. A. Crude Carbo- Fa
Per cent. Per cent. Per cent. Per cent. Per cent.
Sweet potato vines..................... ........... 87.67 1.27 P 2.93 7.77 0.35
Pigweed ............. .... ......................... 95.20 .96 i 1.01 2.71 .09
Honohono........................... ......... 89.43 1.40 1.27 7.58 .32
The sweet potato belongs to the morning-glory family, and many
varieties bloom profusely in Hawaii from November to April.
In ancient times the crop was cultivated, the native agriculturists
evidently appreciating the importance of selection and the value
of alternating the crop with other crops to improve the physical
condition of the soil.
The crop needs moderate rainfall, an abundance of sunshine, and
warm nights for best development. It should be grown in a well-
drained, moderately fertile, loose sandy soil. It responds to favor-
able treatment, making good growth and producing roots of fine
quality on well-prepared land that has been planted with legumes
the year preceding. The depth of plowing usually practiced for corn
is satisfactory for sweet potatoes.
Cultivation should begin when the vines are about 8 inches long.
S Usually from three to four cultivations are sufficient to keep the soil
in good tilth until the field is overrun with vines.
The plant is drought-resistant and produces a crop of roots with
very little moisture.
20 BULLETIN 50, HAWAII EXPERIMENT STATION.
In a test made to determine the effect of pruning on yield, it wI
found that production was considerably decreased when the vineq'
were cut back. Apparently the shorter the vine is cut, the gre it
will be the reduction in yield of roots. Yield is largely influeAeF.j
by the locality and the soil where the crop is grown, the kind g anl
amount of fertilizer used, the cultivation given, and finally by the
variety itself. It may be increased by proper cultivation and th
application of Tertilizers, or by the selection through several genera-;
tions of individual hills producing heavy crops of well-shaped roots'
The period of harvesting differs with the different varieties. Yel4
lowing of the leaves is not always an indication of ripening and ma9i
be due to the disease known as stem-end rot.
Unfortunately the sweet potato is not graded in Hawaii. Stand-,
ardization will hardly become a reality until uniformity of'size,
shape, and color is taken into consideration, and the roots are m tr-.
keted free from defects resulting from careless handling, diseases,
and insect pests. Regular-shaped, uniform, smooth, firm, anid
fresh-looking potatoes should be selected for home use.
The problem of storage can be eliminated by harvesting just
enough potatoes to meet the needs of the wholesaler or the house-
holder. When they are to be held for some time, sweet potatoes
should be carefully stored to reduce to a minimum the loss by
The sweet-potato plant is attacked by a number of insect pests
and fungus diseases which can be brought under control by the use
of proper measures.
In chemical composition the sweet potato compares very favor-
ably with taro, cassava, and potato.
On account of their high feeding value, sweet-potato vines should
be used as feed for farm animals. They are greatly relished by hogs
and dairy cattle, and when it is desired to practice economy of labor
in harvesting, the former may be turned in to harvest the roots.
after the latter have been allowed to pasture the vines.
0 -'1 1
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UNIVERSITY OF FLORIDA
3 1262 08929 0760