Oklahoma Cooperative Extension Service HLA-6022

Sweet Potato Production

April 2022

Lynn Brandenberger
Extension Vegetable Crops Oklahoma Cooperative Extension Fact Sheets
are also available on our website at:
Bizhen Hu extension.okstate.edu
Extension Small Farms

Eric Rebek
Extension Entomologist

John Damicone
Extension Plant Pathology

Production Requirements
Sweet potato is a nutritious root crop that contains significant
amounts of fiber, beta carotene and vitamin C, particularly
in varieties with highly colored roots. It is native to tropical
Figure 1. Harvested sweet potatoes.
areas including Central and South America. This crop thrives
during summer’s warm days and nights, which are required selecting suitable soil; following good production practices,
for optimal growth and root development. When sweet potato including fertility, irrigation, pest management and careful
is managed properly, it has the potential to be one of the more harvesting; handling, curing and storing of sweet potato roots.
profitable vegetable crops grown in Oklahoma. It can be stored
for several months when cured properly and held under proper
conditions, making it possible to market sweet potato through
Expected Yield
an extended period of time. That said, it is not a “get rich quick” Yields of sweet potato in Oklahoma can vary considerably due
crop since it requires significant commitments of capital, time, to site, soil, weather, and crop variety. Under ideal conditions,
and management to make it profitable. Even with the use of very high yields can be attained, but more likely yields will range
mechanical harvesters and other production technology, labor between 300 to 350 bushels (bushel=50 lbs.) per acre of U.S.
requirements are about 60 man-hours per acre. Sweet potato No. 1’s. Another aspect of marketable yield to be considered
production is not recommended for growers who do not plan to are other classes of marketable roots including canners and
grow the crop for several years. Profitable production practices jumbos, which will provide additional income for producers,
include using good seed stock or purchasing certified slips; if markets are available or can be developed.

Table 1. Sweet potato varieties.

Variety-release date Flesh color Notes

Beauregard-1987 Orange Resistant to Fusarium wilt & root rot, Rhizopus soft rot
Bonita- 2011 White Resistant to root knot nematode, Fusarium wilt
Centennial-1962 Orange Resistance to wireworm, Fusarium internal cork
Cordner-1983 Orange Resistant to root knot nematode, early yielder, good slip producer
Covington- 2005 Orange Resistant to root knot nematode
Evangeline- 2008 Orange Resistant to root knot nematode, Fusarium wilt & root rot, Rhizopus soft rot
Jewel-1970 Orange Resistance to root knot nematode & Fusarium wilt
O’Henry- Cream Resistance similar to Beauregard
Southern Delight-1986 Orange Some insect resistance, good slip producer

Websites for further information on sweet potato varieties:

https://lsuagcenter.com/portals/our_offices/research_stations/sweetpotato/features/varieties/sweet-potato-variety-descriptions
https://potatoes.cals.ncsu.edu/sweetpotato/sweetpotato-varieties/
https://kerrcenter.com/publication/heirloom-variety-trial-report-2010-sweet-potato/

Division of Agricultural Sciences and Natural Resources • Oklahoma State University

Sites and Soils
Sweet potatoes produce best in a well-drained, light, sandy Nitrogen- Pre-plant apply 30 pounds per acre of nitrogen
loam or silt loam soil. Rich, heavy soils produce high yields of along with P2O5 and K2O by using a complete fertilizer. With
low-quality roots, and extremely poor, light sandy soils gen- most soils, but certainly sandy soils, leaching of nitrogen will
erally produce low yields of high-quality roots. Both surface occur. It is best to use a split application of nitrogen to prevent
and internal drainage are important in selecting a field. Poor leaching of nitrogen out of the root zone of the crop. In this
surface drainage may cause wet spots that reduce yields. case, 30 pounds would be applied pre-plant and incorporated
Poor internal drainage will also reduce yields. Soils with poor into the soil with the second application of 30 pounds coming
internal drainage are characterized by a high moisture content four to five weeks after transplanting into the field.
and poor aeration, which cause sweet potato roots to be large, During transplanting, a starter solution high in phosphorus
misshapen, cracked, and rough skinned. A three- to five-year can be applied at a rate of one-half pint of solution per plant.
rotation program should be used to reduce the chance of This starter solution can be prepared by adding three pounds
soil-borne disease problems. of soluble 15-30-15 in 50 gallons of water.

Varieties Seed Root Selection

Sweet potato variety selection should be based on several The process of properly selecting, curing and storing sweet
characteristics including market preference, pest resistance, potato roots for the production of slips (vine cuttings) is a
yield, quality and potential for slip production. As with all key step in profitable sweet potato production. Remember,
vegetable crops, market demands are a large factor in variety poor-quality seed roots will not produce the quality slips need
selection, so is the potential for a variety to be productive. It for the establishment and production of high-yielding-sweet
is also important to try new varieties in on-farm trials, and potato crops.
if they are successful, introduce them to customers so they
can provide input for future variety decisions. Sweet potato Steps for maintaining high-quality seed stocks:
varieties to consider are given in Extension Fact Sheet HLA
6035 “Commercial Vegetable Varieties for Oklahoma” available • Maintain a good supply of foundation stock. These are roots
on-line at: https://extension.okstate.edu/fact-sheets/commer- from which seed stock will be grown next year.
cial-vegetable-varieties-for-oklahoma.html. Another good • “Hill-select” foundation stock by selecting hills that produce
source of information on variety selection is Oklahoma State at least four U.S. No. 1 sweet potatoes.
University’s Vegetable Trial Reports MP-164; sweet potato trials
• Choose well-shaped roots that are free from insects and
were completed in 2012, 2013, 2014. Trial results are available
diseases as well as true to variety.
on-line at: https://agriculture.okstate.edu/departments-programs/
hla/research-extension/vegetables/trial-report.html. • Check the flesh color by cutting off about 1/2 inch of root
nearest the stem end. Discard ‘off’ types (mutants) if they
are found.
Soil pH and Fertilizer • Four bushels to six bushels of foundation stock will grow
Sweet potatoes are tolerant of variations in soil pH be¬tween vine cuttings to plant one acre of sweet potatoes for seed
5.5 and 6.8. However, the optimum soil pH for high yields of stock production.
quality sweet potatoes is 5.8 to 6.0. Apply lime if soil pH is
• Produce seed stock from vine cuttings taken from foundation
too low. A crop of sweet potatoes utilizes about 110 pounds
stock and planted on disease-free soil.
of nitrogen, 15 pounds of phosphorus, and 150 pounds of
potassium per acre from the soil. Based on OSU soil test • Handle seed stock potatoes very carefully - with cotton
results, the following amounts of P2O5 (phosphorus) and K2O gloves. Harvest before frost and cure and store separately
(potassium) are recommended (Table 2). Fertility recommen- from other sweet potatoes.
dations based on soil test results for specific vegetable crops • Never let seed stock remain in the field unprotected from
can also be found on-line by going to www.soiltesting.okstate. the sun after digging.
edu. Other fertility recommendations are available in Fact
Sheet HLA-6036 “Soil Test Interpretations for Vegetable Crops.”

Table 2. Phosphorous and potassium requirements for

sweet potato.

Phosphorous Requirements (lbs P2O5/Acre)

When test shows 0 10 20 40 >65
Add lbs. P2O5 120 100 80 45 0

Potassium Requirements (lbs K2O/Acre)

When test shows 0 75 125 200 >250
Add lbs. K2O 120 100 80 40 0 Figure 2. Seed stock for sweet potato production.

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Pre-Sprouting Seed Roots
Pre-sprouting seed roots prepares them for slip production rot, scurf, and root rot organisms. Washing seed potatoes that
and is similar to the root curing process done in the fall fol- are not pre-sprouted before fungicide treatment will remove
lowing harvest. It will shorten the amount of time required for dirt, which reduces the effectiveness of the fungicide. Seed
slip production by approximately a week and increase the roots should not be washed unless they will be treated in a
number of slips by two or three times, compared to roots that fungicide dip before bedding.
are not pre-sprouted. This process should begin with sorting About 12 square feet of bed is needed per bushel of seed
and culling out roots that will not be used for slip production.
Eliminate roots that are cracked, show signs of rot or those potato roots. Fertilize beds with two pounds per 100 square
not of the correct size or shape. Use seed roots that are be- feet of bed using a complete fertilizer such as 10-10-10 or
tween one inch and three inches in diameter. Pre-sprouting 12-12-12. The fertilizer should be mixed with the bed soil prior
requires temperatures to be maintained between 75 F and 85 to bedding the roots. Allow slip beds to warm to 80 F prior to
F and relative humidity of 85 percent to 90 percent with good bedding, then lower the temperature to 70 F or 75 F once
air movement provided by a small fan. Pre-spouting should sprouting begins. Place roots in the bed so they are not in
be started two weeks to four weeks prior to seed roots being contact with each other, then cover them with two-inch mesh
bedded up for slip production. Roots are pre-spouted and ready chicken wire, followed by two inches of clean sand or sandy
for bedding when most roots have sprouts 1/4 inch in length. soil. The mesh wire prevents roots from being pulled up when
Following pre-sprouting, conventional producers can apply a slips are pulled from the beds.
fungicide to reduce potential disease problems; see current After bedding roots, sprinkle water over the bed to slightly
edition of E-832 “Extension Agents’ Handbook of Insect, Plant moisten the soil, but do not overwater and create a soggy wet
Disease, and Weed Control” for recommendations. However, soil. Clear plastic can be placed directly over the plant bed
slips can be grown without fungicides for organic production surface. Remove the cover material when the slips push the
or if labeled fungicides are not available. covering up about two inches. Water the beds as needed to
keep the soil moist. Keep the beds covered with a light-trans-
Producing Slips “Plants” mitting cover such as clear plastic, polycarbonate, etc. until the
plants begin to emerge. Ventilate during the day to control air
Varieties differ in their ability to produce slips, but generally temperature in the beds. Air temperature in the beds should
a bushel of sweet potatoes will produce 2,000 to 2,500 slips be kept under 90 F to produce good-quality plants. Pull plants
in two or three slip harvests. Four bushels to six bushels of when they are about eight inches tall. They should have at
roots will be needed to grow slips for each acre transplanted least five leaves, stocky stems, and a healthy root system. This
in the field. Slips can be grown in cold frames or heated beds. type of plant is best for mechanical transplanting.
It is difficult to produce slips in open field beds in Oklahoma
due to the potential for very cool spring temperatures during If transplants are to be grown for sale, contact the Environmental
the slip growing season. Allow five weeks to six weeks for slip Resources and Horticulture section of the State Department of
production in heated beds and seven weeks to eight weeks in Agriculture (ODAFF), well in advance of production. They will
cold frames. If roots have been pre-sprouted, they will sprout provide regulations and requirements for growing and selling
more quickly and can be bedded up a week later than roots not certified sweet potato slips.
pre-sprouted. Pre-sprouting1 can be done by warming “seed”
State Department of Agriculture (ODAFF)
potato roots to 75-84 F at a relative humidity of 85-90% in a
122 State Capitol
well-ventilated room for two to four weeks.
Oklahoma City, OK 73105
Place pre-sprouted roots in the plant bed with the sprouts
Preparing Soil and Transplanting
upright; a few sprouts will be broken during handling, but this
causes no noticeable reduction in slip production. Roots not
pre-sprouted can be planted either as fungicide-treated or The production of sweet potatoes depends on good soil
non-treated roots in the plant bed. aeration. Good aeration is achieved by proper field selection
and by bedding the field prior to transplanting. Incorporating
Permanent plant production beds are a potential source of
pre-plant fertilizer and “bedding-up” two weeks prior to planting
disease. If permanent beds are used, remove, and discard
allows the bed to settle before planting. The bed should be
the old soil to a depth of 12 inches. Disinfect the bed frames
installed to provide an 8- to 10-inch rise in height after settling
and covering material with a recommended disinfectant. To
and transplanting.
refill the beds, bring in clean topsoil from an area where sweet
potatoes and nematode susceptible crops have not been grown. Early planting is an important factor responsible for high
New soil can be sterilized using soil heating techniques prior yields. Field transplanting should be accomplished as soon
to bedding roots. as possible after slip pulling. If slips must be held for several
days before transplanting, they are best held by “planting”
Before bedding sweet potato roots for plant production, ex-
the bottom end of stems into moist, soilless growing media in
amine roots carefully and discard diseased, mutated, and plastic containers. One container can hold a significant number
bruised roots. Separate the roots to be bedded according to of slips, which will begin to root out after a few days and can
size. This attains an even planting depth and uniform sprout- be held indefinitely. Cull weak and spindly slips for increased
ing. For conventional growers, seed potatoes can be treated yield. Set slips deep with at least three nodes (joints where
with a recommended fungicide by dipping immediately before leaves attach) below ground level.
bedding. Dipping will help control surface infestations of black

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 Figure 4. Click beetle. Photo courtesy Frank Peairs, Colorado
State University, Bugwood.org

Figure 3. Sweet potato flea beetle. Photo courtesy WonGun

Kim, Bugguide.net.

Figure 6. Mottled tortoise beetle (Deloyala guttata).

Photo courtesy Whitney Cranshaw, Colorado State University,
Bugwood.org

Figure 5. Yellowstriped armyworm (Spodoptera orni-

thogalli). Photo courtesy Russ Ottens, University of Georgia,
Bugwood.org

Figure 7. Beet armyworm (Spodoptera exigua). Photo Figure 8. Saltmarsh caterpillar (Estigmene acrea). Photo
courtesy John Capinera, University of Florida, Bugwood.org courtesy Frank Peairs, Colorado State University, Bugwood.org

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 Weed Control
Weed control in sweet potato fields is critical for the first four
to six weeks following transplanting. After this establishment
period, most sweet potato crops will cover the ground com-
pletely and effectively shade out weeds. The critical issue is
how to control weeds prior to the crop covering the ground
completely. In conventional production, several herbicides can
be used to provide weed control during this early period of crop
establishment; consult the current edition of E-832 “Extension
Agents’ Handbook of Insect, Plant Disease, and Weed Control”
for recommendations. In organic production, cultivation by
tractor-drawn cultivators and by hand hoeing would be one
way to approach weed control. Feeder roots soon occupy the
entire bed. To prevent damage to roots, cultivate weeds with
Figure 9. Scarabs or scarab beetles. Photo courtesy Alton equipment that does not scrape or remove soil from the bed.
N. Sparks, Jr., University of Georgia, Bugwood.org Disc hillers, rolling cultivators or other implements that throw
soil to the bed avoid root damage and increase the height of
the bed. A final bed height of ten inches is desired by the last
cultivation, when rapidly growing vines interfere thereafter.
Optimum planting dates in Oklahoma are:
Less damage to vines will occur if rows are cultivated in the
• Southern and Central areas - from May 1 to June 15 same direction each time. Weeds not controlled by chemicals
• Northern areas - from May 10 to June 20 and cultivation will require hand hoeing. In addition, mulching
One- or two-row transplanters are commonly used, but small- (plastic films or organic mulches) could be used to reduce
er operations can transplant by hand if not larger than one weed competition in the field.
acre. Investment in a transplanter as well as a digger should
be considered if planning on growing sweet potatoes on an If the ground has been in sod the preceding season, soil
annual basis. insects such as wireworms and grubs can be a problem.
In-secticides are generally applied either pre-plant or at
Irrigation immediately following transplanting is vital, as stand planting for soil insect control. Otherwise, leaf-feeding in-
losses due to drying out can be a significant factor in reducing sects such as the tortoise beetle and saltmarsh caterpillar
yields. Slips will be damaged if they are planted and left in the are predominant pests of sweet potato. Flea beetles and
field for short intervals of time (more than one hour) without yellow-striped cucumber beetle, and beet armyworms may
receiving irrigation. In Oklahoma, weather can be hot and dry be occasional pests. For specific insect control measures,
during transplanting season with temperatures near or above see the latest edition of E-832 “Extension Agents’ Handbook
100 F. When heat is combined with wind, it creates a serious of Insect, Plant Disease, and Weed Control.”
risk to freshly transplanted slips not watered immediately.There
are several ways to approach this situation. First, if overhead or
furrow irrigation is used, water should be applied immediately Diseases
following transplanting, possibly either watering single rows or The most common sweet potato diseases are scurf, stem rot
small blocks individually to reduce the time from transplanting (wilt), nematodes, black-rot and soft rots. These and other
to irrigation. Second, a transplanter can be altered to apply diseases can cause heavy losses in the field and in storage.
water onto each transplant as it goes into the ground, which They can be prevented or controlled by following recommended
will keep the transplant alive until the irrigation system is able practices in selecting resistant varieties, selecting seed stock,
to apply water. Lastly, if drip irrigation will be used in the field, producing transplants, selecting fields, and growing practices.
it should be installed prior to trans¬planting and be applying Scurf, black-rot and stem rot usually come from disease-infested
water during the transplanting operation, particularly in hand seed stock and can be controlled by a fungicide dip before
transplanted situations. These suggestions will result in very bedding seed roots. Nematodes can come from infested grow-
little loss of transplants and an adequate plant stand. ing beds or soil. Fields known to be infested with nematodes
or other sweet potato diseases should be avoided. A three-
Plant Spacing to five-year rotation should be practiced. Soft rots and other
storage disease problems can be reduced by sanitation and
A common spacing is 12 inches between plants on rows that disinfection of the storage house, proper curing, and careful
are spaced 36 inches to 42 inches between rows (12,500 to handling of the sweet potatoes during harvesting, curing and
14,500 slips per acre). Plant spacing depends on soil fertility storage. For specific disease control measures, see the latest
and availability of irrigation water. In fertile soils, wide spacing edition of the Extension Agents’ Handbook.
results in excessive jumbo roots and rougher potatoes. Close
spacing in very sandy soils may result in undersized roots.
The spacing range given will provide a good starting point for
growers, however adjustments may be considered as needed.

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Figure 10. Black rot, Fusarium stem rot and scurf in sweet potatoes.

Soil Moisture
Inadequate soil moisture is a consistent limiting factor in plow or a middle buster. For a larger planting, a three-point
Oklahoma sweet potato production. Rains are rarely spaced hitch chain-type digger is best. Complex harvesters are
to provide uniform and adequate moisture throughout the now avail¬able for large acreages. These require little labor
growing season. Supplemental irrigation should be available and deliver potatoes directly into containers. Regardless of
to supply up to 1½ inches of water every seven to ten days. the equipment used, it should be adjusted and operated to
Actual needs will vary with soil type, plant size and weather minimize skinning and bruising. Field grading is important.
conditions. Too much water is harmful and will reduce yield Use cotton gloves to prevent skinning. Place No. 1’s and No.
and quality. Moisture should be withheld toward the end of the 2’s in crates together and cuts, cracks, jumbos, and culls in
growing season to condition the soil and roots for harvesting, separate containers. Only store roots that are marketable or
and to discourage the development of cracks in roots and those being held as seed roots for next season’s crop. Size
jumbo size roots. Irrigation systems have been discussed characteristics of the various grades are as follows:
somewhat in the transplanting section, but the primary systems
used in Oklahoma would include overhead and drip irrigation. • U.S. Extra No. 1. (a) Size - (1) Length shall be not less
Over¬head systems could include pivot or linear systems, pipe than three inches or more than nine inches. (2) Maximum
and risers or a side-roll system. Drip irrigation is operated on weight shall be not more than 18 ounces. (3) Maximum
a more frequent basis with irrigations scheduled often daily or diameter shall be not more than 3 ¼ inches. (4) Minimum
multiple times per day. This is the major difference between diameter, unless otherwise specified, shall be not less
overhead and drip systems, i.e., with overhead systems based than 1 ¾ inches.
on applying substantial amounts of water on a less frequent • U.S. No. 1 and U.S. Commercial. (a) Size - (1) Maximum
basis and drip systems applying small amounts of water on diameter shall be not more than 3 ½ inches. (2) Maximum
a very frequent basis. Each system has advantages and weight shall not be more than 20 ounces. (3) Length, unless
disadvantages. Growers not equipped with irrigation systems otherwise specified, shall be not less than three inches
should consult an irrigation engineer to determine which type or more than nine inches. (4) Minimum diameter, unless
of system would work best for their operation. otherwise specified, shall be not less than 1 ¾ inches.
• U.S. No. 1 Petite. (a) Size. (1) Diameter shall be not less
Harvesting than 1 ½ inches or more than 2 ¼ inches. (2) Length shall
Regular field inspection is needed to determine when to be not less than three inches or more than seven inches.
harvest. Sweet potatoes can be harvested any time after • U.S. No. 2. (a) Size. Unless otherwise specified the mini-
sufficient numbers of roots have reached marketable size. mum diameter shall be not less than 1 ½ inches and the
The price for uncured potatoes in late August and Sep- maximum weight not more than 36 ounces.
tember may be high enough to justify sacrificing some
yield to begin digging and marketing early. If the crop is • Length defined as: the dimension of the sweet potato,
to be stored, harvest just before frost to maximize yields. measured in a straight line between points at or near each
When soil temperature falls below 55 F, some damage to end of the sweet potato where it is at least three-eighths
root quality and reduction in their worth for storage and inch in diameter.
slip production will result. Chilling injury can occur even • Diameter defined as: the greatest dimension of the sweet
though a frost has not occurred. In cool weather, remove potato, measured at right angles to the longitudinal axis.
all dug potatoes from the field before nightfall. Prevent
sunscald by removing or protecting harvested potatoes
from the sun. A 30-minute exposure to the sun can cause
sunscald, reducing quality.
Most mechanical harvesters require vines to be cut with a
rotary mower or otherwise removed to prevent interference
with digging. Smaller acreages can be dug with a turning

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Containers Grading and Marketing
Containers are important in handling, proper curing and Whether marketed from the field or from storage, fresh market
storage of sweet potatoes. To minimize handling and reduce sweet potatoes are usually washed, graded and often waxed
injury, containers used to harvest potatoes in the field are before marketing. Poorly shaped, diseased, and damaged
used in curing and storage. Bushel crates or plastic boxes are roots should be graded out to make a good-looking pack.
usually used; however, consider using larger containers like Buyer requirements for grade and size must be met for repeat
plastic bin boxes since there is less potential for root damage sales. Fresh market sweet potatoes are usually packed in
with these containers. One advantage of plastic containers 40- or 50-pound cartons.
is effective cleaning and sanitizing before harvest, whereas Small acreages of sweet potatoes can be marketed by pick-
wooden crates or baskets cannot be sanitized, resulting in your-own methods. Only dig potatoes that will be picked
higher potential for contamination by food-borne pathogens. up by customers during the next hour to prevent sun scald
When deciding what containers to use, consider adoption of injury. Farm to School programs, roadside stands, farmer’s
a standard size and type to simplify transport and storage. markets, and local stores are other possible markets for
small producers. Some processing potatoes are produced in
Curing Oklahoma. Be sure to determine processor requirements prior
to production and delivery. There may be size restrictions on
Sweet potatoes to be stored for later marketing or for seed processing deliveries or potatoes may be delivered field run
stock must be cured immediately after harvest to minimize with culls removed.
storage losses. Do not wash potatoes to be cured and stored.
Curing involves controlling temperatures and relative humidity
and providing ventilation for seven to ten days. Curing is a References
wound-healing process which occurs most rapidly at 80 F to 1Pre-sprouting sweet potatoes, Peirce, L.C. Vegetables,
90 F, a relative humidity of 85 percent to 90 percent, and good Characteristics, Production, and Marketing. 1987, John
ventilation to remove carbon dioxide from the curing area. Wiley and Sons, New York.
Wounds and bruises will heal and a protective cork layer will
develop over the entire root surface. In addition, suberin, a
waxy material, is deposited. The cork layer and suberin act
as a barrier to decay-causing organisms and to moisture loss
during storage.

Storage
Store sweet potatoes between 55 F and 60 F. Do not allow
temperatures to fall below 55 F or chilling injury will result.
Relative humidity should be maintained between 75 percent
to 80 percent to prevent excessive water loss from the roots.
Some ventilation should be provided to prevent carbon diox-
ide buildup.

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Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Director of Oklahoma Cooperative Extension
Service, Oklahoma State University, Stillwater, Oklahoma. This publication is printed and issued by Oklahoma State University as authorized by the Vice President for Agricultural Programs and
has been prepared and distributed at a cost of 20 cents per copy. 04/2022 KG.

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