UNIVERSITY OF Cooperative Extension Service
FLORIDA Institute of Food and Agricultural Sciences
A Vegetable Crops Extension Publication
Horticultural Scienc= Departmet- P.O. 110690 Gainc~vilc, FL 32611 Telephone (352)392-2134
March 10, 1998
I. NOTES OF INTEREST
A. Vegetable Crops Calendar.
II. COMMERCIAL VEGETABLES
A. Hollowheart of Watermelon
B. Roselle (Hibiscus sabdarifa) Observations about a Potential
Niche Crop in North Florida
C. Post Freeze Pepper Mowing
D. Evaluation of Summer Cover Crops in South Florida
E. The Organic Industry
SIII. VEGETABLE GARDENING
A. Vegetable Varieties for 1998 Garden
Note: Anyone is free to use the information in this newsletter. Whenever possible,
please give credit to the authors. The purpose of trade names in this publication is
solely for the purpose of providing information and does not necessarily constitute a
recommendation of the product.
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, age, handicap or national origin.
"rvrIPcD ATn/tc CYTI'TMCIM W1 YV IT A(TlrT TT TI ; fA nMF PrnNrMTr1c' TAITPF f l P lA TAqI rTIVFR;rrY OF FLORIDA,
I NOTES OF INTEREST
A. Vegetable Crops Calendar.
April 28-30, 1998. Sustaining Vegetable
Production in Florida In-Service Training. Seminole
County Extension Auditorium, 250 W. County Home
Rd., Sanford, Florida. Contact Richard Tyson, 407-
323-2500 ext. 5554.
H COMMERCIAL VEGETABLES
A. Hollowheart of Watermelon.
Hollowheart of watermelon is a physiological
disorder manifested by the separation of flesh within
the fruit. It occurs in every production area. The
occurrence and severity vary considerably among areas
and seasons. Frequently, however, loads are rejected
because ofhollowheart. As far as I am aware, there is
no estimate of the economic impact of hollowheart
although it is certain to be significant. It is very
difficult to externally distinguish hollowheart fruit
from fruit with an intact heart although the former
tend to be somewhat asymmetrical. Non-invasive
detection of hollowheart has been attempted by
magnetic resonance imaging (MRI), mammography,
fluoroscopy, ultrasound, and xerography (McCuistion
et al., 1995). Following preliminary evaluation,
fluoroscopy was found to be most effective for
distinguishing hollowheart. Operators were able to
identify 20 of 23 melons with hollowheart using one
view. Detection improved to 22 of 23 fruit with
hollowheart when fruit were viewed from two
directions. The authors suggest that commercial
detection with fluoroscopy could be incorporated into
packinghouse operations. The Japanese are already
using nuclear magnetic resonance (NMR) in Tottori
Prefecture for simultaneous determination of soluble
solids and hollowheart (personal observation).
Most watermelon experts agree that there is a
higher incidence ofhollowheart in crown-set fruit than
in lateral-set fruit, that seedless varieties have more
hollowheart than seeded varieties, and that there are
differences among varieties in hollowheart
susceptibility. Beyond that, there is much speculation
as to the role of water and fertilizer management,
temperature, pollination, and other factors.
Because of the difficulty in understanding the
cause ofhollowheart, little research has been reported.
Results obtained in Japan (Kano, 1993) confirm that
hollowheart occurs more frequently in crown-set (7th
to 8th node) than in lateral-set (20th node) fruit. The
crown-set fruit had fewer but larger cells than the
lateral-set fruit; they also had larger intercellular
spaces than the lateral-set fruit. Accordingly, cell
separation occurs because the fewer, less compacted
cells in the crown-set fruit cannot keep pace with the
expansion rate of the rind. When growth rate was
depressed by defoliation, the inner cell growth rate did
keep pace with the expansion of the rind and
hollowheart did not occur. These results agree with
the notion held by some that watermelon plants that
are 'forced' are more likely to produce fruit with
hollowheart (Wien, 1997; Rubatzky and Yamaguchi,
In preliminary experiments (Maynard, 1995),
the incidence and severity of hollowheart was greater
in 'Jack of Hearts' than in 'Sangria'. Hollowheart in
'Jack of Hearts' was more frequent and severe when
fertilized with 130-60-180 lb/A N-P205-K20 than with
various combinations of higher N and K rates. No
relationship between fruit age (days after pollination)
and hollowheart was established. However, earlier
studies by Elmstrom et al., 1995 showed that there was
a low incidence and severity of hollowheart in 'Jack of
Hearts' and 'Crimson Sweet' watermelon at 5 and 12
days postpollination, but much greater hollowheart at
19, 26, and 33 days after pollination.
Elmstrom, G. W., F. McCuistion, Jr., and D. N.
Maynard. 1995. Incidence and severity of watermelon
(Citrullus lanatus) hollowheart. HortScience 30:427.
Kano, Y. 1993. Relationship between the occurrence
of hollowing in watermelon and the size and number
of fruit cells and intercellular air spaces. J. Japan.
Soc. Hort. Sci. 62:103-112.
Maynard, D. N. 1995. Watermelon hollowheart,
spring 1995. GCREC Res. Rept. BRAI995-28.
McCuistion, F. T. Jr., G. W. Elmstrom, P. Abbott,
B. Steinbach, B. Faile, N. Ackerman, L. Neuwirth,
and C. Spencer. 1995. Fluoroscopy as a non-invasive
method for detecting hollowheart and seeds in
watermelon fruit. p. 140-141 In: G. E. Lester and J.
R. Dunlap (eds.). Proceedings Cucurbitaceae '94.
Gateway Printing and Office Supply, Edinburg, TX
Rubatzky, V. E. and M. Yamaguchi. 1997. World
vegetables: principles, production, and nutritive value.
Second Edition. Chapman and Hall, New York.
Wien, H. C. 1997. The cucurbits: cucumber, melon,
squash, pumpkin. p. 345-386 In H. C. Wien (ed.)
The physiology ofvegetable crops. CAB International,
(Maynard, Vegetarian 98-03)
B. Roselle (Hibiscus sabdarifa)
Observations about a Potential Niche Crop in North
Roselle (also commonly called throughout the
tropics by Rosella, Jamaican Sorrel, Indian Sorrel, Red
Sorrel, Javel Jute, Sorrel, Florida Cranberry, etc.) can
easily be grown as an annual in North Florida from
seed planted no earlier than mid-March in (Union
County). A robust, six-foot high plant similar in
appearance to okra, Roselle begins flowering when day
lengths shorten in the Fall (about mid-October for
North-Central Florida). As flowers open in the
morning, they have a light yellow to sometimes pink
color with a dark red "eye". After pollination, the
calyx becomes fleshy over a matter of a couple of
weeks. November 15 appears to be an average date for
calyx harvest (for fresh juice and processing). Frosts
damage fruit color and taste, leaves for edible purposes
and make dried plant material unmarketable for the
dried floral material industry.
Reported and experienced uses for Roselle
calyxes have been: fresh juice, tea, jelly, "cranberry"
bread, and a very smooth wine (e-mail "Union" a
request for the recipes). Fresh green leaves are edible
and can be cooked up as a vegetable such as in soups
(Caribbean Kalalu, etc.). Linda Landrum (Volusia
Horticulture Extension Agent) suggested we grow
Roselle for the fresh cut foliage industry. We also tried
to produce an air-dried material for the dried "silks"
flower arrangement trade.
Doyal Godwin was recruited as a cooperator
(call 904-496-2874 for seed). Seed were planted
March 15, transplants were set April 15 between 12 -
18 inches apart, with 9 feet between rows. Ten pounds
of 10-10-10 analysis fertilizer were applied per 100
feet of linear row prior to transplanting into a
Flatwoods soil. Ten pounds of 13-4-13 analysis
fertilizer were applied per 100 linear feet of row, as a
side-dress application on September 1. November 21,
plants were harvested and graded (based on floral
industry request of 32 inch stalk/branch minimum
length). Three separate samples of 10 linear feet of
row were quantified, means follow:
Means/10 linear Feet of Row
In-row Plant Spacing = 18.9 inches (1.575 ft.)
Saleable Branches/stems (> 32 in. length) = 58.7
Cull Branches/stems (< 32 in. length) = 23.3
Mature Calyxes = 316
Wholesale fresh cut prices for Roselle ranged
from $2 $3 for a bundle of 5 10 stems; however
retail demand was so low that 15 bundles could not be
moved at that time. One acre could provide an
average of 51,281 saleable stems (probably more than
the entire state's demand at this time). Potential
wholesale value (to the producer) on a per-acre-basis
could be high if there were more demand for the fresh
cut material: 5,128 10,256 bundles/acre times $2 -
$3/bundle (you do the math).
We tried to cut and dry 100 linear feet of
Roselle plant material on clothesline strung under a
pole shed for the dry "silk" materials trade and ran
into a problem "fixing the red color" as a frost froze
and burst the cell contents. Further drying was
unsatisfactory. Drying must be done with controlled
forced heated air much like a tobacco curing barn.
Storage of the large volume of dried material could be
a problem, because it tends to grow mildew when air
Although Roselle holds up well as a fresh cut
plant material (still opening buds after a week in
water) retail florists don't demand it, so wholesalers
are reluctant to purchase large quantities. Roselle
might be a good dried arrangement candidate, with
controlled heated forced air curing. The tremendous
productive capacity of this plant could easily be its own
marketing undoing; plantings should be on a small
trial basis. It is a stunning landscape plant in the
(Jacque Breman, Vegetarian 98-03)
C. Post Freeze Pepper Mowing.
The past two winters have given us ample
opportunity to test the theory of whether or not there is
a benefit to mowing freeze damaged pepper. In the
Winter of '96 southwest Florida experienced three
successive freezes (four in some areas) over the course
of about 30 days whereas Winter '97 featured only one
freeze. Regardless of the year, temperatures dipped
below 28 F (24 in one case) and stayed there for 5 to
8 hours! As cold as it was pepper crops, more likely
than not survived, often supporting one half to two
thirds of the foliage that existed prior to the freeze.
History tells us that these plants will continue to grow
and produce new fruits. But can we "help" Mother
Nature by perhaps mowing away the old tissue to make
room for the new?
Studies conducted by the SWFREC on late
fall planted bell pepper crops that underwent a
freeze(s) in either '96 or '97 may shed new light on the
effects ofmowing. Obviously the stage of crop growth
when a freeze event and mowing occurs can effect the
experimental results. These crops were sufficiently
close in maturity to make the results comparable as the
crown fruit had been picked in the' 96 crop and the '97
crop had not yet been picked when the freezes
The compact growth of winter pepper
generally results in plants that are less than 20 inches
in height. To determine how much foliage (debris)
removal was "too much" we imposed several mowing
treatments from none to severe. In 1996, freeze
damaged 'Enterprise' bell pepper stands were mowed
with an electric hedge trimmer to leave 3 and 6 inches
of plant or left unmowed. In '97, with 'Memphis', a 9
inch plant height was also included. These mowing
treatments removed all dead or damaged tissue caused
by the freeze. Local growers may mow less severely,
removing only the top 3 to 6 inches of top growth,
leaving 14-17 inch plants.
The major impact of mowing occurred at first
harvest and in both '96 and '97 the results were the
same, with one small difference. Pepper that had been
left unmowed yielded no more fruit than the lightly
mowed treatments (Figure 1), but had more culls,
mostly buttons. In '96 the higher cull production of
the unmowed treatment lead to a greater marketable
yield by plants that had been mowed to leave 6" of
foliage (Figure 2). Moderate mowing (6" in '97 and 9"
in '97) resulted in similar yields to the unmowed
treatment. Severe mowing (3" height) however,
consistently yielded fewer total and marketable fruit
than the other mowing treatments.
Unmowed or slightly mowed pepper probably
had more pre-formed flower sites, which resulted in
more fruit at first harvest (and some cases other
harvests as well) than the severely mowed plants.
Conversely, those same flowering sites may have lead
to the increase in culls exhibited in the unmowed
pepper. It should be noted that in '96 the mowing
experiment was established after the last freeze so the
plants were subjected to several weeks of additional
freezes. All that additional cold weather may have
affected newly forming fruit (i.e., more buttons). In
'97 only a handful of days following the mowing
treatments had temperatures that dipped below 500
and no additional freezes occurred. Therefore one
might expect varying results from mowing according
to the number and type (duration, severity, etc.) of
freeze experienced. These studies may however
support the practice of cosmetic mowing. For those
growers who just can't let Mother Nature do her job,
some mowing seems appropriate and may remove
some potential buttons in the process.
(Vavrina, Vegetarian 98-03)
Fig 1. Effects of post freeze mowing on pepper marketable
yield from 18 plants, spring 1997.
4 0 II;i l i, :1 Ili ;
u! 30 I OUnmowed
0 IIM' oll i : iJMowed to 9"
S1'.1 I!'.iI I i 1 I I II AMowed to 6"
20 I'OMowed to 3"
Fig. 2. Increased cull production after multiple freezes
"reduces" yield in mowed pepper, spring 1996.
D. Evaluation of Summer Cover Crops in
Summer cover crops are used for weed control
and to retain nutrients during the heavy summer rains.
They have become an integral part of vegetable
production practices in south Florida. Moreover the
use of cover crops will continue to increase as farmers
seek to improve soil quality and reduce chemical input.
A wide variety of plants are used as cover crops
during late spring and summer in south Florida.
Obviously legumes contribute more nitrogen (N) by N
fixation compared to nonlegumes such as sorghum-
Sudan grass which is a common cover crop in this
area. In order to select the best cover crops for south
Florida, Drs. Herbert Bryan and Yuncong Li initiated
a trial to evaluate ten cover crops in the summer 1997
at the Tropical Research and Education Center,
Homestead, FL. All of the cover crops were seeded on
July 14, 1997, and cut and tilled on Oct. 22, 1997.
Sorghum-Sudan and sunflower were fertilized by 326
lb 10N-OP-12K-8Mg while no fertilizer were applied
for other cover crops. 'Sunbeam' tomatoes were
planted on Dec. 23, 1998. The evaluation of effects of
cover crops on tomato growth with various rates of
fertilizer application is still in progress.
The sunn hemp, Crotalariajuncea L, stands out
from other tested cover crops. It is also called SANN
HEMP, or INDIAN HEMP (Crotalaria juncea), and
is a plant of the pea family (Fabaceae, or
Leguminosae). The plant is cultivated in many tropical
countries for fiber production and as a green manure
crop. Sunn hemp is easy to grow on almost all soil
types. Seeds germinated very well and seedlings
rapidly produced a thick ground cover. It produced
a total of 7,700 lb dry biomass (roots and shoots) per
acre 3 months after seeding. Because it is a legume,
the sunn hemp fixed 182 lb N/ac. We strongly
recommend sunn hemp as a cover crop for vegetables
and tropical fruits in south Florida.
Aeschynomene is a warm-season legume forage and
well adapted to South Florida. It is the only widely
grown summer forage capable of maintaining growth
under root-flooded conditions. It may reach heights of
3 or more feet. Aeschynomene has resistance to most
root-knot nematodes. Aeschynomene evenia, a newly
available species was used for this trial. It produced
2,600 lb dry biomass per acre which was less than that
of sorghum-Sudan. However, it fixed 56 lb N per acre
compared to 27 lb N/ac for sorghum-Sudan.
Aeschynomene also hadvery good ground cover (about
95% of area).
Guar, Cyamopsis tetragonolobus L., also called
"cluster bean" is a legume and well adapted to
locations with more tropical climates. Very little
information is available on the use of this crop in
Florida. The growth of guar in this trial was not good,
and this may have been caused by late planting.
Soybean, Glycine max L. and cowpeas used for
this trial are forages of subtropical legume and grow
well in south Florida. They are made into hay, silage
or seeds and are also used as a cover crop in tropical
countries. Soybean provided better yield and ground
cover than cowpeas.
Peanut, Arachis hypogaea L., is a warm
season/tropical perennial legume native of South
America. It has been reported to grow well in south
Florida. However, it takes a long time to be come
established and cover the ground. It only produced
1200 lb dry biomass per acre 3 months after seeding.
Even though it contributed 26 Ib N per acre through N
fixation, it is not recommended as summer cover crop
for vegetable production. It could be evaluated as a
cover crop for tropical fruit groves in this area.
Savanna stylo (Stylosanthes quionesis), and
Florida balsawood (Ricinus communis L.) also were
planted in this trial, but these crops were not harvested
because of very poor germination and slow growth
Velvet bean and hairy indigo were not included
in this trial but had been observed as cover crops in
1968 by Dr. Herbert Bryan, TREC, Homestead. Both
of their crops grew very poorly in the calcareous soils
in south Florida.
Table 1. Average plant height, fresh and dry yield, ground coverage and fixed nitrogen for eight cover crops grown on a calcareous
soil in Homestead.
Seeding Plant Biomass' Ground coverage Nitrogen in plant
Plant Legume rate Height Fresh Dry Weeds Crop Shoot Root Total
lb/ac inches --- 1000 lb/ac-- --- -%----- % % Ib/ac
Sun hemp yes 40 71.5 30.7 7.7 1.0 99.0 2.5 0.6 182
Sorghum-Sudan' no 60 29.9 11.4 3.0 1.7 85.0 0.9 1.1 27
Aeschynomene yes 40 14.8 11.2 2.6 0.8 95.0 2.4 1.1 56
Soybean yes 70 16.6 9.0 2.3 3.0 66.7 3.1 1.4 67
Sunflower no 45 32.8 14.4 2.2 15.0 71.7 1.6 0.8 33
Cowpeas yes 100 21.1 7.7 1.5 25.0 60.0 2.3 1.3 34
Guar yes 40 18.9 7.2 1.4 27.0 61.7 2.1 1.3 27
Peanut yes 80 5.5 6.9 1.2 7.7 75.0 2.3 1.3 26
Weeds' no nd nd 1.8 0.3 56.7 0 1.3 0.5 4
2 Biomass was calculated by total weight of root and shoot.
Sorghum-Sudan and sunflower were fertilized by 326 Ib 10N-0P-12K while no fertilizer were applied for other cover crops.
Weeds were harvested from control plots and height of weeds was not reported because of variation.
E. The Organic Industry.
This past December, the U.S. Department of
Agriculture proposed federal standards for foods
produced "organically." It took seven years (the
Organic Foods Production Act was first passed in
1990) for the issuance of those proposed rules. Public
comment will be accepted before a final version of the
rules is issued in 1998.
The organic industry did not wait for federal
standards. Several states developed certified organic
professional associations which have led to different
requirements and cultural practices in order to be
qualified to be called organically grown. Florida law
provides for independent certifying agencies such as
Florida Certified Organic Growers and Consumers,
Inc., to assist organic growers to become certified. In
addition, there are three national organizations
providing services to the organic industry: Organic
Crop Improvement Association (OCIA), 3185 Twp.
Road 179, Bell Fontaine, OH 43311, 513-592-4983;
Organic Growers and Buyers Association (OBGA),
1405 Silver Lake Road, New Brighton, MN 55112,
612-636-7933; and Organic Food Production
Association of North America (OFPANA), P. O Box
1078, Greenfield, MA 01301, 403-774-7511.
The U.S. market for organic products has
been increasing by 20% each year for the past five
years, according to several sources in sales and
marketing. They also expect the growers to continue,
driven largely by a health-conscious population and a
general sense of environmental responsibility. As the
market grows, so does the opportunity for growers.
Put into perspective, organic products account for only
1% of national food sales, but now account for about
$3.5 billion annually, compared to $421.8 billion in
conventional food-store sales.
Organic farmers face higher costs because
their natural fertilizers and pest control efforts are
more expensive. Labor to replace mechanization
common in conventional farming is also more
Many think that what people are buying when
they purchase organic foods is a life style, a marketing
aesthetic, an "organic sensibility." They do not really
know what organic is or understand the meaning of
"organic." Is there an Extension need/program here?
(Marion White, Vegetarian 98-03)
II VEG ETABLE GARDENING
A. Vegetable Varieties for 1998 Gardens.
Florida gardeners are fortunate to have
hundreds of vegetable varieties from which to choose
to start their gardens. Seed company catalogs and seed
packets in supply stores display each variety in a
colorful and descriptive manner. What is generally
omitted is the success rate for these offerings under
FLORIDA conditions. All these varieties are offered
nationwide. Each variety will grow better in one area
than another, so there must be some basis for making the
correct selections for Florida. Obviously, gardeners are
looking for wide and varied results. Some just like to
experiment or try something they have heard about. But
most are best served by recommendations that answer
"yes" to the following questions:
a) Are the seeds available
b) Is the variety adaptable to Florida conditions
c) Has the variety produced well in Florida
d) Is there resistance or tolerance to disease and pests
common in Florida
e) Does the product have excellent (or good) quality
f) Does the variety have some unusual characteristics --
heirloom, nutrition, aesthetic, etc.
With these questions in mind, I have compiled
the following list for all Florida. The list contains just
one variety name for each kind or type of vegetable.
Failure of a variety to make the list does not mean it
would not be as a choice or better than those on the list.
Glaring omissions, especially the hybrids, are most likely
due to a limited source of seeds.
Bean, green bush snap
Bean, bush shell
Bean, bush wax
Bean, bush lima
Bean, pole lima
Corn, sweet (white)
Detroit Dark Red
Florida Deep Heart
Early White Vienna
Onion, green bulbing
Onion, red bulbing
Pea, edible podded
California Blackeye 5
Early Cal Wonder
American Purple Top
Squash, summerSN Early Prolific Straightneck
Squash, summerCN Early Summer Y. Crookneck
Squash, zucchini Black Beauty
Squash, winter(acor) Table Queen
Strawberry Sweet Charlie
Tomato, large red Solar Set
Tomato, small red Sweet 100
Tomato, large size Delicious
Tomato, container Micro Tom
Turnip Purple Top
Watermelon, long Jubilee
Watermelon, round Dixielee
Watermelon, icebox Sugar Baby
Watermelon, large North Carolina Giant
(Stephens, Vegetarian 98-03)
Prepared by Extension Vegetable Crops Specialists
Dr. D. J. Cantliffe
Dr. S. M. Olson
Mr. J. M. Stephens
Dr. G. J. Hochmuth
Dr. S. A. Sargent
Dr. C. S. Vavrina
Dr. D. N. Maynard
Dr. W. M. Stall
Dr. J. M. White
The research and extension reports from the Suwannee Valley REC in Live Oak for 1997 are now
complete. If you are interested in receiving a copy of any of these reports, you may use a copy of the listing below
to order by checking those of interest. Send your order to:
Suwannee Valley Research and Education Center
7580 County Road 136
Live Oak, FL 32060
SUWANNEE VALLEY RESEARCH AND EDUCATION CENTER
RESEARCH AND EXTENSION REPORTS 1997
Report No. Title of Report
Send requested copies to:
Response of Cucumber to Meister Controlled-Release Fertilizers
Response of Pepper to Meister Controlled-Release Fertilizers
Evaluation of Several Greenhouse Cluster and Beefsteak Tomato Cultivars in
Mulched Pepper Response to Pursell Polyon Controlled-Release Fertilizers
The Evaluation of Three Pickling Cucumber Plant Populations on Plastic
Mulch Culture in North Florida.
Producing Strawberries in North Florida Using an Outdoor Hydroponic System
Response of Sweet Corn and Snap Bean to Groplex Humate
Response of Mulched Tomato to Meister Controlled-Release Fertilizer
Response of Mulched Pepper to Meister Controlled-Release Fertilizer
Response of Tomato and Pepper to Monopotassium-Phosphate Starter Solutions
Response to Snap Bean, Carrot, and Sweet Corn to Monopotassium-Phosphate
The Evaluation of Three Pickling Cucumber Cultivars on Plastic Mulch and
Bare Ground Culture in North Florida
Efficacy of Monopotassium-Phosphate as a Fungicide for Powdery Mildew
Control in Squash and Muskmelon
Effect of Three Planting Depths on Greenhouse Tomato Yield
Evaluation of Several Yellow Squash and Two Zucchini Squash Cultivars for
Production During Spring 1997 at Live Oak, FL
The Effect ofAmisorb, a Nutrient Absorption Enhancing Polymer, on Pepper
Plant Nutrient Status and Yield
The Effect of Amisorb, on Watermelon Plant Nutrient Status and Yield
The Effect of Fumigant and Mulch Type on Watermelon Yield and Fruit Size
Evaluation of Several Seeded and Seedless "Allsweet-type" Watermelon
Comparison of Different Commercial Fertilizer and Poultry Manure Rates and
Combinations in the Production of Eggplant
Snap Bean and Sweet Corn Response to N Rate and Furrow-Placed Groplex
Mulched Pepper Response to Pursell Polyon Controlled-Release Fertilizers,