INSTITUTE OF FOOD AND
UNIVERSITY OF FLORIDA
A Vegetable Crops Extension Publication
egetable Crops Department 1255 IHSPP Gaincsvillc. FL 32611 Telephone 392-2134
November 14, 1984
I. NOTES OF INTEREST
A. Vegetable Crops Calendar
II. PESTICIDE UPDATE
III. COMMERCIAL VEGETABLE PRODUCTION
A. Row Covers for Commercial Vegetable Culture
B. Mulch and Row Covers on Muskmelons in Florida
IV. HOME GARDENING
A. Cloning Vegetables 4-H project with
B. Master Gardener Activities.
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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
1. Nov. 29, 1984. Annual Allied Industry Workshop. 9:30 a.m. -
3:30 p.m. Manatee County Extension Office, 1303 17th St. -
Palmetto, FL. Person in charge: Dr. Phyllis Gilreath (813)
2. January 29-31,1985 Commercial Vegetable Crops In Service
Training for Extension Agents. (Theme: IPM). Dade Co.
Extension Center, 18710 S.W. 288th St. Homestead, FL.
3. February 6, 1985 Strawberry Field Day. 2:00 p.m. to 5:00 p.m.
Dover AREC (Hillsborough County) Dover, FL.
II. PESTICIDE UPDATE
1. Section 18 for Permethrin on Watercress.
A section 18 specific exemption has been granted for the use
of permethrin (Ambush) for the control of diamondback moth on
watercress. A maximum of 156 acres of watercress in Seminole
County may be treated.
2. Section 18 for Dyrene on Watercress.
A section 18 specific exemption has been granted for the use
of Dyrene (anilazine) for the control of cercospora leaf spot on
A maximum of 130 acres of watercress in Seminole County may
3. Section 18 denied for Oxamyl on SNAPBEANS.
A request for a section 18 for use of oxamyl for the control
of nematodes on snapbeans was not forwarded to EPA.
The denial was based among other things on this being the
fifth year for this use as an emergency exemption and minimal
activity towards registration for this use.
(Stall Veg. 84-11)
III. COMMERCIAL VEGETABLES
A. Row Covers for Commercial Vegetable Culture
Description- Row covers are structures used to protect plants in
one continuous tunnel with the objective of enhancing crop growth and
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Fig. 1. The California two-sheet perforated
poly row cover closed using the
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Fig. 2. The two-sheet system
opened for ventilation.
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Fig. 3. The single-sheet slitted
clear poly row cover.
Fig. 4. The non-woven (spunbonded)
row cover (used without hoops).
Insert showing swatch of cover
yield through moderation of the microenvironment. Most of the row
covers presently in commercial use are constructed from clear
polyethylene supported by wire hoops.
The first successful commercial-scale use of poly covers was made
in San Diego County in California in 1958 but only recently has the
use of row covers for commercial vegetable production rapidly
expanded. Traditionally, row covers have been used in spring to
increase earliness of vegetables. However, new types of row cover
materials allow the extension of the vegetable season further into the
fall and winter.
Present-day row cover technology traces back to research during
the 1950's in Kentucky by E. M. Emmert and to C. A. Shadbolt, 0. D.
McCoy and B. J. Hall in California in the late 1950's and early
1960's; widespread use of row covers did not occur until recently
following research in New England by 0. S. Wells and J. B. Loy. Their
research showed that row covers can be used economically on many
vegetables particularly the cucurbit crops.
Types of covers- There are basically two types of row covers for
commercial use: clear polyethylene and spunbonded or non-woven
polyester and polypropylene. The clear poly covers allow early
vegetable planting resulting in 2-3 weeks earliness and in many cases,
increased total yields over non covered crops. The non-woven
materials increase earliness and total yield for many crops, but also
are effective in extending the harvest season in the fall or winter.
The clear poly can be vented or unvented. The unvented covers
require manual opening to control heat build-up on sunny days. The
vented poly covers consist of a loose fabric material. Similar to
interfacing in the textile industry, and therefore are
self-ventilating. Only minor reductions in light levels (10%-20%)
have been reported for these covers and this has not been enough to
affect crop growth.
Installation- The poly covers require physical support which is
generally achieved through the use of wire hoops. The non-woven
material is light weight (0.6 ounces per square yard) and can be laid
loosely on the plants with no support hoops.
The installation of row covers varies as to type of cover and
geographic region. The California system for cucumbers employs 2
sheets of 36 inch wide, 1.5 mil. perforated clear Poly supported by
9-guage wire hoops (Fig. 1.). The wire (70 inches in length) is
formed in an oval shape so that approximately 30 inches of soil is
covered. The hoops are placed 5-7 feet apart and placed deep enough
in the soil to make a cover that is 15-16 inches tall. Wooden stakes,
1 inch by 1 inch by 28 inches are driven into the ground at 10-15 foot
intervals. Wire (16 guage) is stapled to the top of the stakes and
the two sheets of poly are clipped together at the wire with
clothespins. The other edge of each poly sheet is buried in the soil
at the base of the hoop.
A similar system is used for tomatoes except that 6-foot
stakes are placed at 3-foot intervals with 2 wires attached at the
20-inch height. Hoops are placed at 3-foot intervals. With the
2-sheet system, manual venting is employed by rolling the plastic back
as needed and clipping it to the hoops (Fig. 2.). The covers are
manually closed during night and cool periods.
Because of the labor cost involved in venting the 2-sheet
system a search was begun for a single-sheet, self-ventilating cover.
Research in New Hampshire showed that slitted 1.1 or 1.5 mil. clear
poly ground mulch could be used as a cover. The commonly used 3-foot
wide clear poly ground mulch was widened to 5 feet for use as a cover.
The single sheet can be slitted using two rows of slits down
the length of the cover. The slits are 5 inches long and .75 inch
apart. Perforated poly can also be used as long as the holes are
large enough to allow adequate heat escape.
The single sheet poly can easily be installed with a mulch
laying machine which has been modified to support the roll of cover
above the pre-installed hoops. The hoops are made of 9 guage wire cut
in 63 inch lengths and formed in an oval to cover approximately 30
inches of bed. The hoops are planted at 4-5 foot intervals and the
cover applied over the hoops with the edges of the poly sheet buried
at the base of the hoops. The height of the cover depends on the
clearance of the machines used to install the poly. Recently a
machine was developed which will install the hoops mechanically and
apply the poly cover in one operation.
The non woven covers can be applied without hoops because of
their light weight (Fig. 4.). Like the poly covers they can be
applied with a mulch laying machine with minor alterations to assure
the cover is laid loosely over the row. This usually involves the
addition of a wheel or shaft in the center of the machine over which
the cover flows as it is being applied. The wheel or shaft raises the
center of the cover material while the edges are being buried and
causes the material to be laid with some slack instead of taunt. In
general, the cover is not affected by the wind and usually no rubbing
damage occurs to the plants except for possibly some of the leafy
vegetables such as spinach.
Timing- One of the most critical factors in the successful use of
row covers is the timing of application and removal. Both poly and
non woven materials provided a certain degree of frost protection.
The frost protection is greater when the covers are used without poly
ground mulch and is likewise greater in the fall season than in the
spring season. The slitted poly covers provide 1-2 OF protection
while the non woven covers can give up to 70F protection. However,
the major benefit of the covers is not only in frost protection but in
their overall growth enhancing character. Therefore, time of
application is an important factor in realizing the maximum benefit.
Likewise, time of removal is important because some crops such as
tomatoes and peppers cannot tolerate the extremely high temperatures
that might develop in the covers if they are left on the crop too
long. Care must be practiced to ensure that the covers (especially
the nonwoven) used on bee-pollinated crops are removed when blossoming
Improper timing of application and removal probably is a large
factor in some of the conflicting reports on yield advantages from row
covers. With the advent of new row cover materials such as the
non-woven materials and the pigmented plastics, growers will be better
able to tailor the row cover material to the crop, time of season and
specific prevailing environmental conditions.
Costs- Studies done in Illinois by J. Gerber on muskmelons
compared the cost of materials labor and machinery operation to
install black polymulch, slitted poly covers alone and mulch plus
cover. In 1982 the cost for black poly mulch application was
approximately $230.00 per acre compared to $680.00 for the row cover
alone. The combination of mulch and cover therefore is slightly over
$900.00 per acre. This research showed that melons would have to sell
for only 22.3 cents each to break even on the mulch plus cover system
and 11.5 cents for the mulch alone system. Although the mulch plus
cover system seems less cost-effective than the mulch alone, higher
yields and higher prices for the extra early melons from the covers
make it an attractive system.
Weed and pest control- Very little work has been done on
pesticide use with installed row covers. In general, insect and
disease control has not been a problem because the covers are removed
at about the same time that spraying commences. Weed control,
however, is a problem when the covers are used without black poly
mulch. The covers not only enhance crop development, but also speed
up weed growth. In a muskmelon test, chemicals presently labeled for
weed control failed to control weeds under plastic covers. Rates of
application and phyto-toxicity from volatile chemicals are questions
that need to be answered. Presently, the use of black poly mulch in
conjunction with row covers is the best option in terms of crop growth
enhancement and weed control.
Specific crop responses- The cucurbit crops (muskmelon, cucumber,
squash and watermelon) have responded the best to both types of row
covers. Tomatoes and peppers have responded positively but seem to be
more sensitive to high temperature in the covers making timely
ventilation or cover removal critical. Other crops which have
responded positively to row covers include lettuce, radish and beets.
A portion of the positive response of crops like radish to row covers
(particularly non woven) has been the protection from insects while
the cover is in place.
An integrated system- That row covers alone produce positive
yield responses is well documented. However, their fullest potential
has been realized where covers are used as a part of an integrated
growth intensifying program. Research indicates that this system
should include black poly ground mulch. Likewise, drip, irrigation is
used in the system to ensure that adequate moisture is present under
the covers to support the accelerated growth rate of the plants. The
drip irrigation also facilitates the application of fertilizers to the
plants while the covers are in place.
Future research- Although the row covers are evolving as part of
an overall growth and yield enhancing system, there is much research
needed to refine the components. Additional crops need to be studied
for their adaptivity to the row cover system. New cover materials are
being developed which will need field study. Research and weed
control and fertility in the covers has only begun. Many large
vegetable producing areas, Florida for example, are just beginning to
evaluate the new row covers. The large vegetable states offer immense
potential for row cover use.
In summary, the row cover area is one of the fastest growth areas
in the agricultural plastic industry. It holds much potential for
increasing vegetable production in order to meet specific marketing
strategies. If anyone has questions on this subject, please contact
(Hochmuth Veg. 84-11)
B. Mulch and Row Covers on Muskmelons in Florida.
The use of row covers has been tried for one year in Gainesville.
This was a 2 x 6 factorial experiment with no cover, clear slitted
plastic tunnels, hot caps and three methods of non woven row covers
used with and without plastic mulch. Muskmelons cv. 'Magnum 45' were
direct seeded on March 15, 1984. One month later the row cover
treatments were removed. This was prior to flowering.
There was a tremendous difference in the growth of all plants
under the row covers. Although we were worried that the succulent
plants would sunburn after removal of the row covers in bright sun,
this did not occur. Harvest ran from June 5 to June 22 on the plots.
The results showed that there was no increase in total yield due
to the use of row covers. There was, however, a significant increase
in early yield when row covers were compared to hot caps and no cover.
The lack of increase in total yield but significant increase in
early yield agrees with ongoing research in North Carolina and
Overhead irrigation was used on the plots. Soil temperatures
were taken during the growing period.
One aspect that was noted is that the soil will dry out much
faster under the covers. Whether this is due to the higher soil and
air temperature during the day or to increased respiration from the
larger plants under the covers or to a combination of both is not
known for sure. What is known is that the soil must be moist for the
row covers to add any heat protection during cold periods. In other
areas of the country, drip irrigation is the preferred method to keep
the soil moist.
When we compared the use of plastic mulch in the experiment, it
was found that the mulched plots had significantly more total yield
than the non mulched plots. The mulched plots also had significantly
higher early yields. The increase in yields on black plastic mulch
has been shown before in Florida.
We are planning on repeating and expanding the experiment
this coming spring. A recommendation for the use of row covers cannot
be made on one season's work. The economics and timing of planting
and cover removal must be worked out.
The use of plastic mulch, however, is recommended. The added
expense for the mulch is recovered with higher earlier and total
(Stall Veg. 84-11)
IV. HOME GARDENING
A. Cloning Vegetables 4-H Project With Scientific Appeal.
Want to give your 4-H horticulturists an idea for a bit more
scientific challenge than the old backyard garden seems to provide?
Then turn them on to cloning vegetables. Cloning, also called tissue
culture and in vitro culture, may be high technology, but it is not
magical nor is it too complicated for your more aspiring, bright young
4-H'ers to understand and learn to demonstrate.
The technology of plant tissue culture has come a long way since
the early days of the sixties when its methodology was being worked
out. Today scientists at universities and in private laboratories
everywhere are using it to produce test tube plants. Now, for 4-H
members and high school students, there are kits available for home
and classroom projects. Before we discuss these kits, let's take a
quick look at what cloning is all about.
Tissue culture- cloning, or tissue culture, is a plant
propagation technique for the regeneration of plants from cultured
Purpose- Tissue culture offers many advantages to plant breeders,
genetecists, seedsmen, and others working with plants in some of the
(1) Reduces the amount of time needed to develop new varieties
(2) New plant types (mutants) might result since chromosomal
aberrations are not uncommon in callus derived plants.
(3) Produce disease free plants.
(4) Aids in the manipulation of genetic information.
(5) Allows biotech companies to multiply plants innumerable times,
transfer the clones to fields for seed production, with the sale
of the seeds the ultimate goal.
How cloning is done The following is a very generalized outline
of the procedures followed in the tissue culture of vegetables.
(1) Select propagation material such as shoot tips of tomato, roots
of carrot, or flower buds of broccoli.
(2) Sterilize plant part, then dissect into tissue segments call
(3) Transfer to callus initiation medium.
Note: Each medium contains various ingredients which differ
according to plant parts selected and formula. Murashige and
Skoog developed a medium which is used quite frequently by
scientists. It includes such things as major and minor salts,
sucrose, vitamins, agar, and various concentrations of growth
hormones like IAA, BA, Z, and NAA.
(4) Incubate at proper temperature, light, and humidity conditions
while callus (undifferenentiated cell development) forms.
Usually takes about 7 days for callus to form).
(5) Transfer to shoot development medium.
(6) Incubate at proper conditions. Roots and shoots will develop
usually in about 35 days from the initial placement in the
(7) Transfer tiny plantlets, now having roots and shoots, to the test
tube. Note: some companies are using tiny capsules. An indivi-
dual plant is enclosed in its own individual test tube or c a p -
(8) Culture at proper conditions for growth of roots.
(9) Transplant to soil medium and slowly acclimatize to new growing
The Student Kits Biological supply companies are now offering
for sale plant tissue culture materials, sold separately, or as kits.
Their purpose is for use by students for experimentation. Some kits
include enough materials for one or two students (or 4-H'ers), while
others are larger and have enough for 30 students. All kits come with
instructions. Kits include the culture media along with tools and
other supplies necessary to develop shoots and roots from a piece of
tissue. Of course, each kit is specific for a particular vegetable or
Summary A plant tissue culture project may be just the thing to
stir the imaginative and inquisitive minds of your 4-H members looking
for a more challenging opportunity in 4-H club work. Such a project is
on the (pardon the expression) "cutting edge" of technology in the
field of horticulture. Kits are available (contact me for information)
and are not too expensive. Let's keep older youth in 4-H, and turn
them on to new and more rewarding experiences in horticulture.
(Stephens Veg 84-11)
B. Master Gardener Activities
A graduation ceremony and educational program for 60 Master
Gardeners from Duval, ST. Johns, Putnam, Clay and Flagler Counties was
held in Fifield Hall on October 31. Assistant Dean Jim Brasher
presented certificates after an inspirational talk to the MG's and
agents. Dr. David Hall of the Botany Department presented a discussion
and hands-on class on plant identification. The vegetable specimen
garden tour led by Dr. Mike Lazin, answered many questions on varieties
and production practices for the group. Dr. Bill Becker of Agriculture
Engineering completed the program with a slide show and talk on safety.
On November 8, the current class of 15 MG's from Marion County
attended a similar program at UF. After the Specimen Garden tour, Dr.
Freddie Johnson (Entomology) presented a slide show on beneficial
A slide show on the First Five Years of the Master Gardener
Program was presented by Kathleen Delate in the Garden and Landscape
Section at the Florida State Horticultural Society Meetings in Miami
Beach on November 5, 1984.
Highlands County held an appreciation luncheon for Master
Gardeners who had provided exceptional service in the county. Clarice
Lott and Jim Stephens conducted the awards ceremony during which
plaques were presented.
The first issue of the Florida Master Gardener newsletter, called
the Voluntiller, is scheduled to go out this month. Only Master
Gardeners and those associated with the program will be on the mailing
list to receive the bi-monthly newsletter.
(Delate and Stephens Veg. 84-11)
Prepared by Extension Vegetable Crops Specialists
D. N. Maynard
G. J. Hochmuth
J M. S ephens
Visiting Ext. Agent I
S. M. Olson
W. M. Stall