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represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
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Cooperative Extension Service.
Copyright 2005, Board of Trustees, University
growing Sweet Potatoes for Profit
R. D. William, N. J. Tielkemeier & G. W. Simone
Florida Cooperative Extension Service/ Institute of Food and Agricultural Sciences/ University of Florida/ John T. Woeste, Dean l l
FIELD PRODUCTION AND PEST MANAGEMENT
Your chances of digging 200 bushels or more
of potatoes per acre are good if you followed your
plan in PART I: Planning and Liming and the plant-
ing instructions given in PART II: Field Preparation
and Planting. Now you must control the weeds,
add more fertilizer, and learn to identify and con-
trol insect and disease pests of sweet potato.
Watch for pests or problems. Every few days,
walk through your sweet potato field. Look care-
fully for signs of insects or poor plant growth.
Once in awhile dig or uncover a few roots to look
for insects or diseases. Learn to identify the im-
portant pests of sweet potato. Then, you can
choose the right method to control the pest before
it destroys your whole crop.
Look carefully for insects or diseases every couple
Added or supplemental fertilizer should be ap-
plied alongside the sweet potatoes as a side-
dressing during the growing season. If you split
the complete fertilizer before planting, you should
side-dress the other half in 1 or 2 applications
about 3 to 6 weeks after planting.
Small farmers can dribble the fertilizer along-
side the sweet potato row. Keep the fertilizer off
the sweet potato leaves or you will burn them.
Cover the fertilizer with soil soon after you finish
applying the fertilizer.
Larger farmers can use a tractor and side-
dressing equipment. Place the fertilizer about 4 to
5 inches deep near the edge of the ridge or bed.
Be careful to place the fertilizer far enough away
from the plants to keep from cutting the sweet
potato roots. This is also a good time to kill weeds
and keep the bed formed by cultivating with disc
After heavy rains or long periods of cool
weather, be sure to apply some nitrate (NOs) type
of nitrogen and more potassium in your side-dress
fertilizer. This will keep your plants growing when
ammonium (NH4) type of nitrogen cannot change
to the nitrate form fast enough in the soil. You
should try to apply about 10 Ibs of nitrogen (N)
and 30 Ibs of potassium (K20) per acre.
Most root crops need an even amount of water in
the soil throughout the season. Otherwise, the
roots will crack or be poorly shaped. Water your
sweet potatoes whenever the soil begins to dry.
You can test the soil for moisture by digging
some soil from near the sweet potato roots. Hold
the soil in your hand and squeeze. Now open your
hand. If the soil crumbles and does not keep the
shape of your hand, it is too dry and you need to
water your sweet potatoes.
HERBICIDES FOR SWEET POTATOES
Time of Amount of
Herbicide application product/
name to crop acre Remarks
Amiben* Pretransplant 2 gallons Apply broadcast at planting.
Dacthal W-75* Pretransplant 14 Ibs. Apply broadcast at planting.
Vernam 7-E* Pretransplant Depends on Requires soil incorporation. Read
(Vernolate) type of bed label carefully to choose the correct
preparation method of applying Vernam for your
Enide 50W* Posttransplant 8 Ibs. Apply over sweet potato plant after
Dacthal W-75* Posttransplant 14 Ibs. Apply at last cultivation up to 6 weeks
(DCPA) after transplanting.
*Indicates trade or commercial names.
TILL THE SOIL AND CONTROL WEEDS
Sweet potato vines grow very fast. They cover
the soil within 6 to 8 weeks after planting. The
thick cover of sweet potato leaves shades the
weeds and keeps them from sprouting or growing.
Weeds that grow before the vines cover the soil
can be killed by shallow hoeing or tilling. When
the sweet potatoes are young, tilling with a rolling
cultivator will kill most small weeds. Later, use
disc hillers to cover weeds in the row and keep the
bed formed. But be careful to keep from cutting
sweet potato roots by tilling too often or too deep.
Chemical weed killers or herbicides can be ap-
plied to control weeds in sweet potato fields. These
chemicals slow or stop the growth of weeds. Herbi-
cides also can harm your crop if you apply the
chemicals the wrong way. Be sure to follow the
instructions printed on the label.
Herbicides must be applied evenly over the
whole field. A tractor and sprayer is needed to
apply these chemicals. When using herbicides for
the first time, apply them to a small trial area.
Then, you can learn how to apply the chemicals
without injuring your whole crop. For more facts
about herbicides, read Extension Circular 196.
The herbicides listed in this chart can be used
to control weeds in sweet potatoes.
LEARN TO USE PESTICIDES CAREFULLY
The use of pesticides is very important for good
crop production. But you must use pesticides care-
fully because many are poisons. Read the pesticide
label and instructions before each use. Follow all
cautions and warnings. Keep all pesticides in the
same container or package that they come in. Store
in a safe, dry place that is kept locked. Keep out
of the reach of children. Get rid of empty packages
or containers by following the instructions on the
label. Note carefully the time limit between the last
time you can apply the chemical and the date you
can harvest the crop.
Some pesticides listed in this production guide
may be for "restricted" use only. If so, you will
need a "restricted pesticide applicators license."
You can get a license if you study carefully and
pass a test. Ask your County Agent for more in-
formation about getting a license.
Pesticide labels and regulations change often.
In fact, some labels may have changed since this
guide was printed. Ask your County Agent or local
farm supply dealer about lawful pesticide uses for
sweet potato production.
Several kinds of insect pests can harm sweet
potatoes. Insects that eat sweet potato leaves do
not cause much damage. Control of these pests is
recommended only when many leaves are eaten by
the insects. Control methods are listed in the chart
or at the end of this section on insect control.
Insects that feed on sweet potato roots are
always bad pests. Damaged roots must be culled
or thrown away. Also, diseases can enter through
the insect hole and cause rotting or decay.
Watch for insect damage by removing a little
soil from the roots every few weeks. If you see
an insect or insect damage, use the following
photos and words to help you identify the insect.
Then, you can choose the right control method, if
one is needed.
Many pesticides may be poisons. Handle them
WIREWORMS are yellow worms with tough skins, usually /2 to 1 inch long. Their bodies appear to have rings and feel
slippery. Wireworms eat a ragged hole in the root, usually late in the season. Sometimes, the worm will eat completely
through the root.
SWEET POTATO FLEA BEETLES are tiny, black beetles that jump like a flea when disturbed. Eggs are laid in the soil
and hatch into slender white worms called larvae. The larvae feed on the root leaving shallow tunnels just under the skin. As
fhe root grows, the tunnels split open. A winding or uneven scar remains on the skin. The potatoes can be sold if the scars
M O.,A- L- 1i_
GRUBS are the "C-shaped," large white immature stages of scarib beetles. The grubs eat rough, shallow holes on the un-
derside of the root.
CUCUMBER BEETLES cause very little damage to sweet potato leaves, but the larvae can damage young roots. The larvae
are from 1/V to /2 inch long and light yellow. They have brown heads and a dark brown spot at the rear of the body. The
larvae eat small, round holes through the potato skin and form cavities under the skin. The holes or scars usually are formed
SWEET POTATO WEEVIL is the most damaging of all sweet potato pests. The adult weevil looks like a large ant. Look
for a bright orange mid-section and a dark colored head with a snout. Eggs are laid in the vines or roots. Pale white larvae
hatch within a week. The larvae eat the flesh or tissue of both the sweet potato stem and root. After the larvae feed a little,
a bitter taste is produced and the potatoes are not fit to eat. Weevils can infest potatoes both in the field and in storage.
Control of the sweet potato weevil is limited. At
this time, no insecticides are registered for weevil
control in the field. So, you must keep weevils
from entering your fields. Kill all weevils that come
in by accident.
Here is what you can do to control the sweet
Buy "certified" plants that are free of weevils
and other insects. Look carefully at the plants be-
fore planting. Remove and burn all plants that may
Rotate crops and fields. Do not grow sweet
potatoes in the same field two years in a row.
Plant new fields at least one mile from old
After harvest, disc old fields often to kill old
potatoes and reduce the weevil's food supply.
When cultivating your crop, throw extra soil
around the base of each plant. This will reduce the
number of eggs laid in the roots.
Select varieties that develop roots deeper in
the soil because they will have fewer weevils.
Clean all grading and storage areas com-
INSECTICIDES FOR SWEET POTATOES
Insecticide Amount Minimum days
Insect formulation per acre to harvest Remarks
Wireworms Diazinon 14G 21 lbs (Should be Apply over dry leaves
no problem) when roots begin to
Dyfonate 10G preplant 40 Ibs (Should be Mix preplant application
Postplant 30 Ibs no problem) with disc or apply over
leaves when roots begin
Dasanit 15G 30 Ibs band or Mix into soil with disc
46 Ibs broadcast before planting.
Parathion 10G 30 to 40 Ibs -Mix into soil with disc
Flea Beetles & Thiodan 2 EC 1 qt 1 day Apply over leaves at
Cucumber Beetles planting and 7 to 10
Parathion 4EC 1 pt 15 days Apply over leaves at
15WP 3 Ibs planting and 7 to 10 days
later. Parathion is
hazardous and should be
applied by a trained
Caterpillars Parathion 4EC 1 pt 15 days Same as above.
Leafhoppers 15WP 3 Ibs
Sweet potato No insecticide registered for weevil control in the field. However, sweet
weevils (field) potato weevil has been less of a problem where Thiodan was applied for
flea beetle control.
(Stored Imidan 5% Dust 2 to 4 oz per Wash in clean water
potatoes) 50 Ib bushel before selling.
Methoxychlor Dilute with talc -Wash in clean water
(Marlate) to 25% methoxychor before selling.
and apply 1 Ib per
20 crates of dry
Sweet potato diseases can attack the roots
either in the field or in storage. The best way to
control diseases is to keep them from infecting
your potatoes. Buy "certified" plants that are free
of disease. Inspect them carefully before planting.
Here are some good ways to reduce the chances
Cut vine cuttings from the tips of your "cer-
tified" plants. Be sure these cuttings appear to be
free of disease or insect damage.
Plant the cuttings in another field that has
been prepared correctly. These plants will take a
little longer to grow the potatoes. But more good
quality potatoes can be produced from these vine
cuttings than from the mother plants.
Rotate your fields every year. Also plant potato
varieties that resist disease. (See the section on
varieties in Part II of this guide).
At harvest, handle your potatoes carefully to
reduce bruising and scuffing. Always clean your
equipment and storage areas to reduce infecting all
potatoes if disease is present.
Learn to identify the following diseases:
Black rot and scurf diseases form spots on the
underground stems and roots. These spots are
called lesions. Black rot lesions are slightly
shrunken, round black spots. Diseased plants pro-
duce low yields. Roots or infected areas taste
Scurf lesions are gray-brown spots. These spots
grow only on the skin of the potato. Roots look
discolored, but yields are not reduced.
Control: Black rot and scurf diseases are caused
by molds or fungi that live in the soil. Prevent and
control these diseases by following all of the steps
Buy "certified" plants and plant in fields free
of sweet potato diseases.
Cut vine cuttings one-inch above the soil sur-
face. These cuttings will have less chance of being
infected with black rot or scruf.
Rotate your mother plant nurseries and your
growing fields with other crops such as corn, small
grains or pastures every year.
Wilt or stem rot disease is caused by a fungus
that lives in the soil. Plants with stem rot often wilt
in mid-day. Cut open stems of wilted plants length-
wise. They will look dark-brown along the edges
and inside the stem. Diseased plants and lower
leaves will look yellow. Growth will be stunted.
Young plants may die.
Control: Buy and select disease-free plants. Ro-
tate fields and crops.
Wilt or Stem Rot
Surface rot and soft rot are two diseases that
infect potatoes just before harvest or after har-
vesting. Surface rot produces round spots up to
an inch across. The spots are brown rather than
black like black rot. Unlike scurf which occurs
only on the potato skin, surface rot can infest the
whole potato. Stored potatoes that are infected
with surface rot will lose water from these spots
until only a hard, dry potato remains.
Control: Do not harvest potatoes when the soil
is too wet. Try not to bruise potatoes during har-
vest and handling. Rotate sweet potatoes with
other crops where the disease is present.
Soft rot disease is a fungus that often grows on
old bread in the home. This fungus produces tiny,
powder-like seeds or spores that float in the air.
These spores can infect the potato roots when the
soil is very wet before harvest. Soft rot can infect
bruised or injured roots during harvest, handling
or storage. Soft rot produces a gray, fuzzy mold on
the root surface. Diseased roots first turn soft.
Later, they become dry and hard.
Control: Avoid bruising and injuring potatoes
during or after harvest. Cure and store roots under
warm, moist conditions.
Internal cork disease is caused by a virus. Sweet
potatoes that have internal cork can be identified
only by cutting the root. When roots are sliced
open, dark-brown or black "corky" spots will be
found in the flesh.
* Control: Plant only internal cork-free sweet po-
tato varieties. DO NOT save seed potatoes from a
field with this disease.
1. Florida Extension Circular 440, "Growing
Sweet Potatoes for Profit."
PART I Planning and Liming
PART II Field Preparation and Planting
PART IV Harvesting and Marketing
2. Florida Extension Plant Protection Pointers
60, "Insects Affecting Sweet Potatoes."
3. Florida Extension Circular 196, "Chemical
Weed Control for Florida Vegetable Crops."
4. Florida Extension Circular 225, "Commercial
Vegetable Fertilization Guide."
5. Florida Department of Agriculture, Division of
Plant Industry, "Florida Sweet Potato Weevil
6. USDA Agriculture Handbook 388, "Sweet Po-
tato Culture and Diseases."
7. USDA Farmers Bulletin 1059, "Sweet Potato
8. USDA Pamphlet 874, "The Sweet Potato
Since extension circulars are revised from time to
time, be sure to obtain the latest copy.
Acknowledgements: The authors thank the many
staff and faculty members of the Institute of Food
and Agricultural Sciences (IFAS) including J. M.
Nehiley, L. Carter, P. F. Korshing, J. A. B. Pierce,
L. T. Christenberry, J. R. Yelvington and W. S.
Cheshire for helping develop and evaluate this
Special contributions were made by: The use of trade names in this publication is
F. A. Johnson and J. E. Brogdon Insect solely for the purpose of providing specific
Control information. It is not a guarantee or warranty
of the products named and does not signify
We also acknowledge the support from the IFAS recommendation of the product to the exclu-
Sf R D P sion of others of suitable composition.
Center for Rural Development Programs. were p d by te
Photographs in Part III were provided by the USDA.
This publication was promulgated at a cost of
$327.00, or 0.109 cents per copy, to provide new
information on growing sweet potatoes to both large
and small producers.
Single copies are free to residents of Florida and may be ob-
tained from the County Extension Office. Bulk rates are
available upon request. Please submit details of the request to
C. M. Hinton, Publication Distribution Center, IFAS Building
664, University of Florida, Galnesville, Florida 32611.
COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
Cooperative Extension Service, IFAS, University of Florida
and United States Department of Agriculture, Cooperating
K. R. Tefertiller, Director