INSTITUTE OF FOOD AND
UNIVERSITY OF FLORIDA
A Vegetable Crops Extension Publicatior
Veclable Crops Department 1255 HSPP Gainesville, FL 32611 Telephone 392-213.
I. NOTES OF INTEREST
A. Vegetable Crops Calendar
II. COMMERCIAL VEGETABLE PRODUCTION
A. Tropical Root Crops Cassava
III. HOME VEGETABLE GARDENING
A. Reaching Our Home Horticulture Clientele
The Institute of Food and Agricultural Sciences is an Equal Employment Opportunity Affirmative Action Employer authorized to provide research,
educational information and other services only to individuals and institutions that function without regard to race, color, sex, or national origin.
COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS, STATE OF FLORIDA, IFAS, UNIVERSITY OF
FLORIDA, U. S. DEPARTMENT OF AGRICULTURE, AND BOARDS OF COUNTY COMMISSIONERS COOPERATING
I. NOTES OF INTEREST
A. Vegetable Crops Calendar
The Twenty-second Annual Florida Tomato Institute will be held
September 8, 1983 at the Sandpiper Bay Conference Center, Port St.
Lucie, Florida. The Institute will precede the Annual Joint Tomato
Committee/Exchange Conference at the same location on September
9-10, 1983. A program of the conference follows.
A room is set aside for the demonstration of both the FAST and
FAIR computer systems. There will be people available both
Thursday and Friday for help if anyone wishes to try the system
FLORIDA TOMATO INSTITUTE
Port St. Lucie, Florida
September 8, 1983
9:00 Registration and Coffee*
(*courtesy of ICI Americas)
10:00 Introductory Remarks
10:15 The 1982-83 Tomato Season
Wayne Hawkins, Florida Tomato Committee/Exchange, Orlando
10:30 Critical Needs for Research
D. N. Maynard, Chairman, Vegetable Crops Dept., Gainesville
10:45 F.A.I.R., Florida Agricultural Information Retrieval System
Ken Pohronezny, AREC, Homestead
11:00 F.A.S.T., Making the Freeze Forecast Available to the Private
Sector J. F. Gerber, Executive Director Florida
Agricultural Service and Technology Inc., Gainesville
11:15 Changing Input Costs on Tomatoes
Jose Alvarez, AREC, Belle Glade
11:30 Federal Crop Insurance A Pilot Program for Tomatoes -
R. L. Brown, Collier County Extension Service, Naples
11:45 Discussion and Questions
12:00 Adjourn for Lunch
1:30 Tomato Stand Establishment
H. H. Bryan, AREC, Homestead
1:45 Fertility Management Overview of 1982-83 Fertility Problems
G. A. Marlowe, Jr., Vegetable Crops Dept., AREC, Bradenton
2:00 Fertility Management Using Seep Irrigation
P. H. Everett, ARC, Immokalee
2:15 Fertility Management Using Overhead Irrigation
S. J. Locascio, Vegetable Crops Dept., Gainesville
2:30 Bacterial Diseases of Tomatoes
J. B. Jones, AREC, Bradenton
2:45 Pesticide Update Fungicides
T. A. Kucharek, Plant Pathology Dept., Gainesville
2:55 Pesticide Update Insecticides
F. A. Johnson, Entomology & Nematology Dept., Gainesville
3:05 Pesticide Update Nematicides
R. A. Dunn, Entomology & Nematology Dept., Gainesville
3:15 Pesticide Update Herbicides
W. M. Stall, Vegetable Crops Dept., Gainesville
3:20 Questions & Discussion
II. COMMERCIAL VEGETABLE PRODUCTION
A. Tropical Root Crop Cassava
The following article is taken from a manuscript for a book
chapter authored by S. K. O'Hair, AREC, Homestead, Florida. Due
to its length the article is an extremely abridged version of part
of the chapter; published here with consent of the author.
The tropical root crops cover a number of different plants of
which cassava, the edible aroids and yams are the most important.
Their value is in the production of starch-filled storage organs
that serve as a low cost source of carbohydrates in the diets of
many people in the tropics. Additionally, one to all are often
utilized in small farm mixed plantings in the tropics. With the
movement of people from the tropics to Europe and North America,
these crops are now found in non-traditional distant markets. Due
to their relatively long growing season and requirements for warm
temperatures for optimum growth, tropical root crop production in
Europe and North America is limited to regions that have a long
frost-free growing season such as Hawaii and Florida in the United
States and Italy in Europe. Each crop has special qualities and
growing requirements; therefore, each will be covered separately
during the coming months.
Cassava (Manihot esculenta L. Crantz) is one of the more
important of the tropical starchy staples, being recognized inter-
nationally through the development of crop programs at the Inter-
national Center for Tropical Agriculture (CIAT), Call, Colombia
and the International Institute for Tropical Agriculture (IITA),
Ibadan, Nigeria. Also known as yuca (Spanish), manioc, tapioca
(French) and mandico (Portuguese), it is a very adaptable crop and
is considered to be outstanding in its food producing ability and
economy of production. Originating in Brazil and Paraquay, pro-
duction has spread throughout the tropics and subtropics, with wild
Manihot species growing as far north as Arizona. In the U.S.,
cassava was used during the Civil War as a calorie source and as a
substitute for corn starch. It has been grown along much of the
Gulf of Mexico and as far north as Atlanta and Memphis. The en-
larged roots are the plant part most often consumed. In parts of
East ad West Africa and Southern America the young tender shoots
are cooked as potherbs.
A member of the family Euphorbiaceae, cassava is a short-
lived perennial tropical shrub growing one to four meters tall.
Adventitious roots varying in shape from long and slender to
globose arise from stem cuttings and enlarge during the starch
The white starch-filled flesh of the root is crisp and uni-
formly fine grained. On a fresh weight basis, root starch concen-
tration ranges from 5 to 40% depending on cultivar, environment
and plant age. Cassava starch is 13 to 21% amylose and is con-
sidered to be eaily digested and suitable as a partial substitute
for maize or barley starch. Prepared in manners similar to pota-
to, cassava provides low-cost calories to the diet. There is 0.9
to 2.4% protein in the peeled fresh root and 1.1 to 4.90% in the
peel (the bark and phloem tissue), which is often discarded in the
preparation process. Leaves are high in protein ranging from 19
to 40% on a dry weight basis. However, the sulfur amino acids are
low or missing in roots and leaves. Thus, diets need the addition
of other foods high in methionine to make the protein intake com-
Although the processing of cassava roots into food items is
not a major industry, there is potential for expanded use of such
products. Cassava cakes, made from baked or fried grated root.
and "fufu", made from cooked roots that have been pounded and
slightly fermented, are sold commerically in some regions. Farin
is a dried product that is used in the Caribbean as well as in
Brazil, where it is known as farinha. In this case the roots are
peeled and grated, followed by juice extraction through pressing
and drying either in the sun or in a large heated pan. Much stir-
ring is required during the latter method to prevent the product
from burning. Once the farin is lightly browned, it can be stored
for several months in a protected location. It can be reconstitu-
ted to make a porridge or sprinkled over stews, cooked vegetables
or meats. Roots can be chipped, dried and processed into flour or
they can be pelleted and used for animal feed. Cassava flour can
be used as a partial substitute for cereal flour in the prepara-
tion of bread, with little or no noticeable effect.
Without processing, the root flesh and leaves may be toxic
due to the presence of free and bound cyanogenic glucosides (HCN).
The total HCN content varies considerably with cultivar, environ-
ment and plant age. Cultivars low and high in HCN are termed
"sweet" and "bitter", respectively, due to a bitter flavor that
accompanies the HCN. Levels in the peel, peeled root and leaves
ranged from 5 to 77, 1 to 40 and 0.3 to 29 mg/100 g (fresh wt.),
respectively. Juice extraction, cooking the leaves or roots, fer-
mentation of fresh roots, or combinations of these are processing
treatments that aid in reducing HCN levels to safe levels.
Toxicity from cassava may develop when considerable quanti-
ties are consumed over a period of time. This is particularly
true if the prepared cassava has high HCN concentrations and the
diet is poorly balanced nutritionally.
The largest producer of cassava is Brazil, followed by
Thailand, Indonesia, Zaire and Nigeria. World production is cur-
rently over 122 x 106 Mt/annum, of which over 60% is produced in
these countries. U.S. production is limited to backyard gardens
in Hawaii and 30 to 150 ha in southern Florida. Yields vary con-
siderably depending on cultivar, plant age at harvest and local
environmental conditions, which include fertility, pest and di-
sease presence and climate. Average world yields are 8.8 Mt/ha,
while the highest experimental yields exceed 60 Mt/ha/annum.
Thus, the potential for higher world yields is great.
Cassava grows best in warm tropical climates; however, culti-
vars have been selected for adaptation to mountainous, subtropical
and other ecological zones. It grows well in many soil types, and
it excells over other crops in production on marginal, unused
lands. However, it does not tolerate saline or water-logged con-
Land is usually worked with a plow or hoe prior to planting.
Stem cuttings 20 to 25 cm long are selected from the lower mature
sections of healthy plants and planted either flat two to five cm
below the soil surface or at a 450 angle to vertical position in
the soil with the top one-third exposed. The preferred position-
ing varies with soil conditions and planting time. If the soil
depth is shallow, or if it is dry and an extended dry period is
likely, then horizontal planting with complete soil coverage is
recommended. Otherwise, the latter positioning is preferred,
since lodging potential is reduced with the even root distribution
that develops around the base of the cutting. Stem polarity must
be observed during the planting process, since the cutting will
not survive if planted upside down. A fungicide and pesticide dip
is recommended as well as careful handling of the cuttings prior
to planting. Currently most cassava is planted by hand. However,
machines are being developed to handle this task for large plant-
ings. It is best to plant in moist soil at the start of the rainy
season. Raised beds or mounds are advised for areas where drain-
age is poor, land is shallow or erosion is likely to be a problem.
In the latter case, beds should follow the land contour. Plant
spacing of 1/ m2 is common. However, mixed croping is often prac-
ticed in the tropics. Mixed plantings can include other root
crops, cucurbits, maize or beans as well as young more permanent
plants such as bananas, plantains, citrus or cacao.
In the tropics, fertilizer is not generally used unless cash
crops are also in the same planting. Cassava responds most to
phosphorus fertilization. It has been demonstrated that VA mycor-
rhiza benefit cassava by scavenging for food and supplying phos-
phorus to the roots. Excessive fertilization can reduce root
yields by encouraging top growth at the expense of starch deposi-
tion in the roots. If available and needed, a (6-12-12) analysis
fertilizer is generally applied in split applications of 750 kg/ha
at planting or soon after and again one or two months later.
Unless rainfall is minimal, less than 750 mm, cassava does not re-
spond to supplemental irrigation. In drought situations, cassava
survives by dropping its leaves to conserve moisture. New leaves
develop when rains return.
Weed competition during the early stages of plant growth is a
major factor leading to yield reduction. Pests and diseases are
numerous and highly regional with the exception of a few.
Bacterial blight and brown leaf spot are the most common disease.
Mites, thrips and whiteflies are the most common arthropod pests.
Several nematodes have been found in association with cassava.
However, only root-knot on some genotypes has consistently been
associated with damage when soil populations are high. Genetic
resistance has been identified for many of the pests and disease,
and hybrids are being developed with these resistances. When
disease resistance is not present, yields can be reduced by 50% if
healthy, pathogen-free cuttings are not utilized.
Harvesting begins 8 to 10 months after planting with plants
being pulled from the ground by hand as the demand for roots
develops. Plants can be left in the ground for several years with
the roots becoming larger each year. Problems with this are that
the roots become fiberous and have a lower starch concentration.
Carbohydrates are translocated from the root to support leaf
growth at the beginning of the next season and later are deposited
as starch only in newly formed root parenchymatous tissue near the
outside of the root. Thus tissue produced during the previous
season looses and never regains its high starch concentration.
Pre-harvest removal of the upper stems and leaves instills length-
ened postharvest storage life to the roots. The mechanisms for
this are not yet understood. Otherwide, harvested roots will
maintain good quality for only a few days after harvest. Internal
breakdown with flesh darkening and localized rotting are the most
common postharvest problems. In the tropics, marketing takes
place in local street markets whereby a days supply of roots is
harvested and sold from a sidewalk stand. Some fresh roots are
shipped to the larger cities and even exported by air to North
American and European markets.
III. HOME VEGETABLE GARDENING
A. Reaching Our Home Horticulture Clientele
Extension works with both agricultural and non-agricultural
groups. Home gardeners are generally included in the latter
group. According to a national survey by the USDA, "A Profile of
Clientele Served by County Agricultural and Natural Resources
Extension Staffs", both groups receive a large amount of time from
Those of you agents who are concerned most with the large
suburban non-agricultural audience in your county may be interest-
ed in how you work with them in your programs as compared with how
others around the country work with them.
By far the greatest number of people reached by agricultural
agents is in the non-agricultural audiences, comprising 68 percent
of the audience reached. Commercial farmers reached make up only
12 percent of Extension's audience nationally.
Agents in 562 counties surveyed said they are reaching these
non-agricultural people through the following media:
Percentage of suburgan nonagricultural audience reached by:
Radio/TV News Phone Publications Magazines
36.7 35.4 23.9 23.8 20.8
Office visits Mail Meetings Demonstrations Site Visits
16.2 15.1 10.2 7.8 7.4
It is interesting to note that the same methods were used
with about equal effectiveness for both urban and rural counties.
For commercial farmers, direct mail was the most widely used
method, comprising 70 percent of the contacts made by extension.
Here is a brief summary of some of the methods and techniques
presently included in Florida home horticulture extension pro-
A. Prepared message agent goes to the station and reads it
"live" or "taped for airing".
B. Prepared message taped and sent to the station for airing
(by IFAS-Gainesville or by Agent).
C. Interview format live: agent is questioned "live-on-the-
D. Interview format taped: agent interview is taped for later
E. Talk show local live-on-the-air call in questions and an-
A. Interview show (live or taped agent is host).
B. Interview show (live or taped agent is guest).
C. Cable channel Extension in county has exclusive use of the
D. Video tape made by t.v. staff for later use.
E. Video tape made in Gainesville by IFAS for agent to use on his
F. Video tape made in Gainesville by IFAS and sent to t.v. sta-
tion for airing (agent may not be involved).
G. Regular t.v. programming from U.F., like the Old Sunshine
A. Fairly expensive video cassette players required for showing
tapes at meetings or other events.
B. Make tape yourself if you have a camera.
C. Video tapes prepared at Gainesville are sometimes available to
D. Video tapes, such as "IFAS Vegetable Gardening Tips" are made
in Gainesville and sent directly to t.v. stations.
E. Tapes may be filed and used when timely.
F. Used in meetings, self-help clinics, etc.
G. Many county facilities outside extension have V.C. equipment
for loan or rent.
A. Lecture or conference via telephone to distant audience.
B. Requires simple, inexpensive hook-up equipment.
C. Provides live participation.
D. Variety of visuals may be used by prior arrangements.
E. From speaker's standpoint, telelecture eliminates costly
travel and expenditure of time.
F. From viewer's standpoint, telelecture broadens inputs from
5. Slide/Cassette Tape Programs
A. Involves slide show synchronized to a narrated cassette tape.
B. Tape may be shown and slides shown by separate equipment, and
coordinated by agent, or synchronized electronically.
C. Ideal for lobby displays.
D. Great for self-teaching with minimum monitoring.
E. Allows preparation of a complete instructional program for
showing by an inexperienced person.
F. Agent may prefer to narrate slides rather than use the cas-
A. Secretary responds to phone request for information by playing
a short cassette tape message.
B. A timely gardening tip-of-the-day may be recorded and heard by
dialing an advertised number.
A. Extension personnel everywhere are looking for ways to utilize
computers in programming for home horticulturists. Data
banks, filing, and use of software on gardening, such as gar-
den planning, are some of the possibilities. Expect a rapid
increase in gardening related software development in the next
B. IFAS is providing vegetable gardening programs to be used by
commercial computer subscription services in South Florida.
8. Master Gardener Program
A. Florida, like many other states, is rapidly expanding the MG
program (over 15 counties now).
B. Involves volunteers training to become extension helpers, and
giving 50 hours or more of personal time to educational activ-
A. Successful gardening techniques may be demonstrated by Exten-
sion in a number of ways. Most involve a model garden located
strategically, as near the ag centers, community garden sites,
or down town.
B. Excellent method for use by Master Gardeners.
10. Other Common Methods Not Involving One-on-One
A. Newsletters/circular mail
B. Newspaper/magazine articles
C. Publication hand-outs dispensed from racks
D. Meetings, clinics, camps
As defined in the U.S.D.A. Profile Survey, "a county program
consists of the total Extension educational effort with mass
media, meetings, tours, bulletins, and other information as plan-
ned and carried out by county leadership with clientele groups".
Because the non agricultural group is the largest, representing 87
percent of the adult population, and receives only 11 percent of
total Extension staff time (see USDA Misc. Pub No. 1415), mass
media methods must be expanded and utilized to their fullest ex-
tent if Extension is to continue to make the sort of impacts our
supporters expect of us. We are reaching only 13 percent of our
audience as compared with 70 percent of the commercial farmers.
Prepared by Extension Vegetable Crops Specialists
D.N. Maynard S.P. Kovach
Chairman Assistant Professor
G.A. Marlowe M. Sherman
Professor Assistant Professor
W.M. Stall J.M. Stephens
Associate Professor Associate Professor
A. McDonald '
Anyone is free to use the information in this newsletter.
possible, please give credit to the authors.
The use of trade names in this publication is solely for the purpose
of providing information and does not necessarily constitute a recom-
mendation of the product.
Statement: "This public document was promulgated at a cost of $
or 4 per copy for the purpose of communicating current technical
and educational materials to extension, research and industry person-