S. L. BROTHERS
Circular 222 November 1961
NIVEI TY OF FLORlIDOAl7
AGIULUA EXESO SEVC
S. L. Brothers, Assistant Agronomist, Agricul-
tural Extension Service, and Fred Clark, Associate
Agronomist, Agricultural Experiment Station
COOPERATIVE EXTENSION WORK IN
AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
Agricultural Extension Service, University of Florida,
Florida State University and
United States Department of Agriculture, Cooperating
M. O. Watkins, Director
PLASTIC COVERS FOR
TOBACCO PLANT BEDS
There are two principal methods of growing
tobacco plants in Florida-cold frame and open
field production. In the cold frame method, cheese
cloth covers have been used since the early 1870's.
Open field production of plants is of recent origin.
It developed in central and southern Florida as a
result of the severe outbreak of blue mold in the
tobacco area in the 1930's.
Plants produced in the open fields of central
and southern Florida, especially in the vegetable
growing areas, are exposed to virus diseases that
affect tobacco and may be attacked by nematodes.
Either or both of these pests could seriously affect
the farmer's income, if present in plants produced
in the open field and transplanted on the farm.
The principal benefit of cheese cloth covers
has been protection against frost and wind dam-
age. Open field production does not provide such
With both the cold frame and open field meth-
ods, the grower has had to prepare seedbeds early
and hope for favorable weather. Usually, it has
taken longer to produce seedlings of transplant
size than to grow the crop after it was trans-
planted to the field.
Development of better procedures for produc-
tion of tobacco plants appeared desirable. Use of
better planted covers seemed worthy of investi-
Research.-In the fall of 1957, the Agronomy
Department of the Florida Agricultural Experi-
ment Station began tests of several types of cov-
ers for tobacco cold frames. The results of four
years of research during the period 1957 to 1961
clearly show the superiority of translucent plastic
film as a cover for tobacco seedbeds.
Translucent plastic film was superior to cheese
cloth in every experiment. The superiority was
measured in faster germination, more plants,
faster plant growth, more vigor and reduction of
leaching losses of plant nutrients. Benefits not
measured included protection from freezing tem-
peratures and reduction of damage by blue mold.
Figure 1.-Top and bottom pictures show beds that were
covered with plastic. Center bed was seeded
at same time as top bed but grown under
;rF -4~-i:;r- -
t.;' d -
In the 1958 plant production season, the cold-
est on record in Florida, tobacco seedlings under
plastic reached transplant size in 64 days, while
those grown under cheese cloth required 96 days.
The value of plastic film was found to extend to
the field. Higher yields and better quality were
produced from seedlings grown under plastic film
than from plants grown under cheese cloth.
Demonstrations.-During 1960, county agents
and tobacco growers carried out a total of 41 dem-
onstrations in 17 counties. All types of side walls
and frames were used, and numerous ways of at-
taching the plastic to the frame were tried. One
type of frame and a means of attaching the plastic
that met with much favor are shown in the pic-
ture on the front cover.
Over this frame the plastic was stretched and
stripped down the center, with each edge sand-
wiched between 1" x 2" strips. The plastic was
rolled to the center from each side to permit wa-
tering or other treatment of the plantbed.
Most beds grown under plastic films were suc-
cessful, and farmers were well pleased with the
Preparation of the seedbed should begin four
or more weeks ahead of seeding date. Clear all
roots and other trash from the bed area and turn
or disk the soil, leaving a well prepared bed. This
bed should be in good tilth and leveled by raking
just before treating it for control of weeds and
About one week before seeding date, apply
not more than 150 to 200 pounds of a 6-9-3 tobacco
plantbed fertilizer containing one percent water
soluble magnesium for each 100 square yards of
plantbed. Spread fertilizer as uniformly as pos-
sible and rake it into the top one to two inches
of soil. The bed should be moist at the time the
fertilizer is applied.
Application of organic fertilizers, such as
chicken manure or stable manure, is not recom-
mended for beds to be covered with plastic film.
Figure 2-Cross ties, logs or sawed
In late December or early January, a week or
more before seeding the bed, but after it has been
fertilized and when the temperature is above
500 F, apply one pound of methyl bromide per
100 square feet of bed area, using the following
procedure for a 100-square-yard bed:
1. Subdivide the bed into three plots of equal
size, and place a gas receptacle, such as an open
quart Mason jar or a Number 2 tin can, at the
center of each plot in an upright, or slightly slant-
2. Place the outer end of the tubing of an ap-
plicator in each receptacle and extend the tubing
two or more feet beyond the outside of the bed.
3. Stretch a gas-proof cover over the entire
bed and to the ground outside the bed on all sides,
and bank edges of cover with soil to prevent escape
of the gas to be released.
4. Release three pounds of methyl bromide
gas into each receptacle, by use of the special ap-
5. Remove cover 24 to 36 hours after treat-
ment. Never leave it on longer than 48 hours re-
gardless of the temperature. Rake the soil with a
handrake to expedite escape of the gas fumes, and
allow at least 48 hours to elapse before seeding.
r may be used for plant bed sidewalls
Methyl bromide is highly poisonous. The gas
should be released and the cover removed from
the windward side of the bed so that any escaping
fumes will be carried away from the operator.
The varieties of tobacco grown in the past have
contributed to the good acceptance of the Florida
crop by tobacco companies. If you have had suc-
cess with the variety you have grown in the past,
by all means stick to it. If you wish to change to
a supposedly better variety, plant only a few rows
to see what it will do before making a complete
change. Varieties that have been and still are
good include Hicks, White Gold, 402, Golden Har-
vest and Golden Cure.
Seed may be sown about 60 days prior to the
date you desire to have transplants ready to go to
the field. For most growers this will probably be
around January 10. Use 1/4 ounce of seed of the
chosen variety per 100 square yards. To facilitate
uniform distribution, the seed may be mixed with
four to eight pounds of weed-free dry sand or dolo-
mitic limestone. Firm the soil and sprinkle the
bed lightly after sowing to settle soil around the
Sidewalls of 6- to 10-inch materials should be
fixed in place around the seeded area. A substan-
tial frame will be needed to support the plastic
film. Suggested types are shown in Figures 1
and 2. Strips 1" x 4" for the center ridge and
1" x 2" for the rafters will give a strong frame
that will withstand wind and rains.
After construction of the frame has been com-
pleted, stretch the plastic cover over the frame
and fasten it to the sidewalls. One side of the
plastic may be fastened permanently. If possible,
let the permanently attached side be toward the
prevailing wind. This will make it easier to re-
place covers when watering and carrying out other
management operations. The other edge of the
plastic cover may be sandwiched between 1" x 2"
strips or it may be reinforced with masking tape
and fastened. Poultry netting over the frame
will give additional support. Each grower must
devise a means for attaching the plastic so that
it may be removed from time to time for watering
and otherwise managing the bed. Be sure the
plastic is stretched tight to prevent it from sag-
ging when it rains and to prevent it from tearing
during high winds. Beds of 35 to 50 feet in length
rather than 75 to 100 feet may facilitate handling
of covers. This would be especially helpful if plas-
tic is sandwiched between 1" x 2" strips. Covers
that are not elevated, used in some tobacco areas,
are not recommended in Florida, particularly for
If the bed is moist at the time the plastic cover
is fastened on, watering may not be necessary for
two or three days. The bed should be inspected
daily, however, and water applied as needed. Good
soil moisture during the first two weeks is neces-
sary for germination and establishment of a good
stand. Daily watering may be necessary. Don't
let the moisture condensation on the under side
of the plastic deceive you into thinking that soil
moisture is adequate. This can happen and the
soil still be too dry for good germination. This
is particularly true on the deep sandy soils com-
monly used for beds in Florida.
Perforated hoses have been used to supply
moisture in some demonstration beds. Width of
bed and water pressure will need to be considered
in determining the number of lines of hose that
will be needed. Over-watering should be avoided,
as plant food may be leached below the root zone.
Ventilation usually is not necessary during
the first five or six weeks after seeding. After
this, however, watch your plants daily and give
some ventilation if necessary. Several days with
outside temperatures of 750 may make ventila-
tion necessary. Usually, leaving each end open
will be sufficient. If it is necessary to apply top
dressing fertilizer to plants under a plastic cover,
mix five pounds of nitrate of soda in 50 gallons of
water and sprinkle the mixture on 100 square
yards of bed. If dry material is substituted, pull
plastic cover back and allow several hours for
plants to dry before applying the fertilizer. After
it is applied, be sure to sprinkle with water to
wash it off the plants. Never apply dry fertilizer
of any kind when plants are wet.
PREVENTION OF BLUE MOLD
Although the higher temperatures under plas-
tic covers seem to reduce damage by blue mold, a
regular dusting or spraying program for control
of this disease should be carried out. Spray or
dust with ferbam or zineb from the time plants
are the size of a dime until they are pulled for
transplanting. Rates of application and intervals
between applications of dusts or sprays should be
the same as recommended for beds with cheese
cloth covers. Excessive amounts of ferbam or
zineb dust may be harmful under plastic film.
ADVANTAGES OF PLASTIC COVERS
1. Use of plastic covers for tobacco seedbeds
permits seeding three to four weeks later than
when cheese cloth covers are used, thus reducing
total management time.
2. Less seed is required, and more rapid
growth with less fertilizer is obtained. One-
fourth ounce of seed is sufficient for 100 square
yards of bed when plastic covers are used.
3. Plastic films reduce water loss by evapora-
tion. Nevertheless, it is advisable to check soil
4. Plastic films provide better protection
against cold and frost than does cheese cloth.
5. Under plastic a greater number of plants
survive, have better root systems, and reach prop-
er size by the most desirable transplanting date.
6. Blue mold does not appear to be as dam-
aging under plastic, probably because of the high-
er temperatures reached during the day under
7. Fewer applications of fungicides, insecti-
cides and fertilizer are needed, since the plants
under plastic are protected from wind and rains.
8. Increased field yields have resulted from
the use of plants grown under plastic films.
9. Plastic film used for fumigating the bed,
providing it is not black plastic, can be used over
the plantbed, thus eliminating the need for pur-
chase of an extra cover.
Good tobacco yields depend upon early plant-
ing of good tobacco plants in the field; plastic cov-
ers can be used with "predictability" rather than
with "probability" to help growers produce good
If suggested management practices are fol-
lowed, tobacco growers should be able to produce
plants more economically than formerly and they
will have better plants.
Table 1.-Data on Tobacco Seedling Production Using
Plastic and Cheese Cloth Bed Covers.
Monthly Summary Seeding to
Max. Min. Plastic cloth
Jan. '58 ..-........... 60.5 37.5 64 96
Feb. '58 .............. 62.6 34.9 64 96
March '58 ............ 72.4 50.2 64 96
Jan. '59 ............ 68.9 41.8 60 88
Feb. '59 ........... 75.4 54.6 60 88
March '59 ........... 73.3 49.9 60 88
Jan. '60 ............. 69.4 43.2 72* 98
Feb. '60 ............. 70.2 43.4 72* 98
March '60 ............ 72.1 44.7 72* 98
Jan. '61 ............. 63.8 40.1 74* 95
Feb. '61 ............. 74.4 47.2 74* 95
March '61 ............ 81.1 54.0 74* 95
51-year average 4-year average
Jan. .... .............. 68.9 47.2
Feb. .................... 70.4 47.9 68 94
March ............ .75.9 52.5
* These plants could have been transplanted from 2 to 5
days earlier. Transplanting was delayed because cheese-
cloth covered plants needed more size for transplanting.