FLORIDA AGRICULTURAL EXTENSION SERVICE
UNIVERSITY OF FLORIDA
INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES
Vegetable Crops Department
October 22, 1968
TO: COUNTY AGRICULTURAL AGENTS
IN THIS ISSUE:
1. Sweet Potato Notes
A. Variety Evaluation
B. Weed Control
C. Insect and Disease Control
E. Harvesting and Handling
F. Marketing and Promotion
G. Hot Water Bath for Sweet Potatoes
2. Plastic Mulch Applicator and Bed
Shaper for Strawberry Culture
3. Short Notes
A. New Lettuce Varieties
C. USDA Bulletins
0. New Telephone Number
1, Sweet Potato Notes.
Some notes from the Sweet Potato Short Course held at Abraham Baldwin
Agricultural College, Georgia Coastal Plain Experiment Station, Tifton,
Georgia, October 3, 1968.
Florida sweet potato growers should only use the information presented
here where It Is better suited to their production situation than that
Information presented in Florida Agricultural Extension Service Circular
97A, "Sweet Potato Production Guide."
A. Variety Evaluation.
Dr. S. A. Harmon gave an evaluation of varieties.
now in Georgia 12,000 acres of sweet potatoes supplied more
farm markets than 120,000 acres did a few years ago.
Seed potatoes certified are a direct measure of v<
clarity. In 1968, the varieties were certified In this orde
(61,000 bu.), Centennial (16,000 bu.), Rose Centennial (14,1
Early Sweet (2,300 bu.), Gold Rush (500 bu.), Bunch P. R. (
Julian (25 bu.), and several others.
He stated that
sweets to off-
r: Georgia Red
000 bu.), Red
COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS. STATE OF FLORIDA, COLLEGE OF AGRICULTURE.
UNIVERSITY OF FLORIDA, U. S. DEPARTMENT OF AGRICULTURE. AND BOARDS OF COUNTY COMMISSIONERS. COOPERATING
Atlanta market quotations show Georgia Red always quoted at a
higher price than any of the others listed. Although monthly price average
In 1968 for Georgia Reds was about $4.00, they start off in July at $8.00,
znd drop to $3.00 per bushel by September.
Coastal Sweet has by far the best eating quality and highest per-
centage of marketable yield, very good shape; skin color is dull, yellowish
tan so that buyers do not like it. Late 160 days. Best variety for local
sales to known, repeat customers.
Red Cliff Looks excellent, high yield.
Market Keeping Sprouting Disease Processing
Variety Yield accept. quality ability resistance quality
Georgia Red good good good exc. tolerant fair
Centennial exc. fair fair fair tolerant good
P. R. fair fair good good susc. fair
Gold Rush good poor fair fair tolerant exc.
It takes at least 6 years and, more likely, ten years to produce
,n acceptable variety from a breeding project. Sweet potatoes are very
mutable so that new strains and varieties have been developed from existing
ones. In the last 25 years, over 50 varieties have been officially named
In the United States. Only five or six are being grown commercially.
Characteristics that cannot be observed directly are also occurring in
sweet potatoes but are not being detected (such as internal quality).
In the development of a new variety, the following things are
1. Yield 5. Culinary Quality
2. Appearance 6. Disease Resistance
3. Keeping Quality 7. Insect Resistance
4. Sprouting Ability 8. Drought Resistance
B. Weed Control,
Dr. Norman Glaze, USDA, recommended Eptam at 7 pounds per acre
as a post-transplant over the top application; Vernam as a pre-plant appli-
cation 4 Inches deep and Incorporated at 1l pounds per acre. (Vernam is
qot cleared as an over-the-top application.) He suggested Diphenamid and
Dacthal as also being labeled for use. He mentioned amiben but stated
that methyl ester amiben was better, but not yet labeled on sweet potatoes.
C. Insect and D!sease Control.
Insect and disease control was covered by a panel. Nothing new
In control measures. Two publications were handed out and are available
from the University of Georgia Cooperative Extension Service in Athens,
"Control of Sweet Potato Insects," Ent. 2-3, Bul. 668.
"Diseases of Sweet Potatoes," Leaflet No. 47,
Dr. Harmon thoroughly discussed the fertilizer requirements for
sweet potatoes, He said nitrogen was only needed in low-to-moderate
quantities and was essential for fibrous (feeder) root growth elongation.
Phosphorus needs are quite low; however, he does not recommend
the elimination of phosphorus from fertilizer.
High potash is essential at fleshy root formation time for best
Among the minor elements, only Boron has been found to be
essential for good root production (applied at 10 pounds borax per acre).
More than this may be harmful. Use of dolomitic limestone to correct pH
is recommended. Calcium is also essential for good fleshy root formation.
May be quickly corrected by applying gypsum to growing crop.
Sweet potatoes take the following quantities out of the soil:
Yielded N P205 K20 Ca Mg
300 75 20 115 35 10
400 100 26 153 46 13
A starter solution with 4 to 6 pounds of 10-52-8 In 100 gallons
of water definitely pays. Phosphorus should be high and potash low to
prevent salt burn. Apply i-1 pint per plant.
Use 1,000 pounds 5-10-15 plus 500 pounds 10-0-10. Applications
should be split with one-third at planting time in three bands placed as
Second application or first sidedressing 30 days following planting and
third at lay-by. First applications should include the 5-10-15 and the
two sidedressings the 10-0-10. Dr. Harmon has had severe damage from
liquid fertilizer applied in the soil.
Broadcast application of fertilizer requires the use of one-
third more than banded and increases the weed problems significantly.
He has found no significant difference among different formulas
and sources except Rainbow mix 5-10-15 was slightly better--456 bushels
marketable per acre versus 442 bushels.
Total Yield (bu.) with 5-10-15
Irrigation 1,000 lbs. 2,000 lbs. Inches Applied
In /4 days 566 612 28
1 in /8 days 506 583 28
None 419 402
Dr. Harmon recommends to keep soil wet for first 30 days. For
the next 25-30 days, allow some water stress to occur and next 60 days
apply I to 1i inches every 10 days and never allow to dry out.
E. Harvesting and Handling.
A panel, moderated by Area Specialist Jim Barber, discussed pro-
blems and practices. A grower, Mr. Harry Lutz of Leesburg, Georgia,
explained his successful operation. He showed a film of his Johnson
Harvester, made In North Carolina, In use in his field. An extension of
the steel-rodded digging belt took the roots past six graders who selected
roots and placed them Into pallet boxes. He pointed out that soil condi-
tions need to be right--not too wet or too dry--to avoid skinning and
damaging sweet potatoes. Some matted soil appears necessary on the belt
to cushion roots as they pass down the grading line. The machine must be
operated slow enough to avoid damage. His machine traveled at 1.5 mph.
Fork-lifts take the pallets to the curing house within a few
minutes after digging. After curing, they are dumped into a washer, then
feeder roots and stems are broken off and are graded out. They pass through
a Botran (fungicide) tank and then are packed into corrugated fiber board
cartons. He said 95 percent of Georgia sweet potatoes are packed in
corrugated containers. Prior to digging, Mr. Lutz "conditions" his potatoes
by mowing the tops five days before harvest.
F, Marketing and Promotion.
A sweet potato broker said that 90 percent of the sweet potatoes
ha sells from Georgia go south (to Florida). He stressed a need for depend-
ability of supply and quality for a grower to be successful. To promote
sweet potatoes, a sweet potato queen has been selected.
Field demonstration conducted by Dr. S. A. Harmon showed bedding,
transplanting, digging and grading.
G, Hot Water Bath for Sweet Potatoes,
Bathing sweet potato sprouts In hot water helps destroy fungi
chat cause scurf and black rot, diseases that can severely damage sweet
Scurf and black rot fungi infecting a sweet potato seed root
spread onto the sprouts and eventually onto the new crop of sweet potatoes
produced by the replanted sprouts.
In the field test, ARS plant physiologist, L. J. Kushman at
Raleigh, N. C., and plant pathologist, E. M. Hildebrand at Beltsvllle, Md.,
almost completely halted the spread of scurf to the new crop by immersing
the basal portions of diseased sprouts for 10 minutes in water warmed to
1200 F. before replanting.
Although the seed roots from which the sprouts were obtained con-
tained some black rot, almost no black rot developed on the treated plants.
This bath in no way injured the plants.
If hot water treatment of sprouts can be used commercially to
control scurf and black rot, it may prove more effective than chemicals
because heat may affect disease organisms within the tissue as well as on
2, Plastic Mulch Applicator and Bed Shaper for Strawberry Culture Prepared
by Richard Cromwell, Extension Agricultural Engineer.
The equipment on the attached drawing is used for mechanically applying
plastic mulch and shaping the bed. These two operations are often done In
.;parate operations presently, but the growers could save considerable
expense and time by combining equipment and doing as many operations as
possible at once.
The tractor which draws the mulch applicator can be equipped with a
fumigant applicator mounted forward on the tractor. The fumigant used is
only effective where the plastic traps it and keeps it from being lost to
The operational principles of the equipment are:
1) At the beginning of each row the end of the plastic film is
covered with dirt for holding the end stationary and for sealing.
2) The shaping sled (bed former) is lowered down onto the previously
made bed to the desired position.
3) As the tractor moves forward, the trencher makes a small trench
and the plastic film Is forced into by the two tires which roll along
on the plastic directly behind the trencher. The plastic is held in position
by soil which Is placed along the edge by the disc shown !n the drawing
The disc Is positioned to the outside of the plastic and the depth of the
disc can be adjusted to get the best results.
r"- ---' '
PLASTIC MULCH APPLICATOR AND BED SHAPESR
A. Two New Lettuce Varieties.
Two new head lettuce varieties developed in Texas and by USDA
are Valtemp and Valrlo.
Zinophos has been cleared for use on strawberry plants as a bare
root dip. Immerse roots only for 15 minutes at the rate of one pound
active per 100 gallons of water (I,00 ppm active lnredlent) Zinophos
cannot be used on Fla. 0 or Dabre&k at more than 30 ppm without phytotoxicity.
greens, and turnip greens
0.75 Ibs. actual per acre
labeled for use on collards, kale, mustard
pre-plant soil Incorporation treatment at
a tolerance of 0.05 ppm.
Du-Ter fungicide developed by Thompson-Hayward Chemical Company
has recently been labeled for control of early and late blight on potatoes.
Reports received indicate It Is a very good material and should be used
at 5 ounces per 100 gallons of water. The tolerance has been established
at .05 ppm on tubers.
C. USDA Bulletins.
Received two USDA Bulletins.
Bul. 2232, "Commercial Growing of Asparagus"
Bul. 2233, "Commercial Growing of Watercress"
D. New Telephone Number.
Beginning November 9, the university is going on a direct dial
system and anyone In the Vegetable Crops Department can be called direct
by dialing 392-1794.
When we move into the new building later, there will be additional
telephone numbers added. We will notify you when we get moved around the
first of January, 1969.
Mason E. Marvel
Associate Vegetable Crops Specialist
V. F. Nettles
Vegetable Crops Specialist
/ James M. Stephens
Assistant Vegetable Crops Specialist