PROTECTING LEATHERLEAF FERN FROM COLD DAMAGE WINTER 1980-81
R. H. Stamps and A. R. Chase .'. .. '. i
IFAS University of Florida- L.
Agricultural Research Center-Apopka ....,
ARC-A Research Report RH 81-10
Two types of weather conditions, radiational fro1 a r l ffFtil
can cause cold damage to leatherleaf fern, Rumohra ad i-Rai4+ta naq
frosts, which result from rapid radiational cooling of plant material, occur
on clear nights when the sky acts as a black body and absorbs radiant heat from
fronds. Airmass frosts result from the introduction of a cold air mass with
temperatures below O0C (320F). These conditions can and do damage the above
ground portion of unprotected leatherleaf fern in Florida. Visually detectable
injury of immature fronds usually occurs after exposure to temperatures below
-1C (30F) (5). Preliminary tests have indicated that immature fronds are
capable of surviving air temperatures below -1C (30F) for several hours but
damage to the fern makes them unmarketable (W. H. Bodnaruk, Jr., personal
During the winter of 1980-81 dry bulb temperatures at least as low as
-13C (9F) were observed at ferneries in Central Florida. Due to fern losses
caused by these cold temperatures and high seasonal demand during the late
winter and spring, growers who successfully cold protected their fern capitali-
zed on the situation and maximized their economic returns in 1981.
Plants can be cold protected by changing the plant and/or by changing the
plant's environment. Intrinsic plant cold hardiness can be increased through
genetic manipulation. Chemicals, including fertilizers, also can be used to
increase the cold hardiness of some plants. Traditional efforts to protect
leatherleaf fern have centered around heating the fernery. Most leatherleaf
ferneries use overhead sprinkler irrigation to add heat. This method can result
in deleterious effects to the fern and the local environment caused by the large
volume of water used for cold protection. Application rates in excess of 103,000
L/ha/hr (11,000 gal/A/hr) are common (10) and cause leaching of nutrients and
pesticides from soil, damage soil structure and may cause root and rhizome
damage (3). Excess soil water and the resultant lack of adequate oxygen in the
root zone can aid disease development and reduce root and top growth. Intensive
ground water withdrawals also can cause problems such as salt water intrusion,
temporary losses of water to domestic wells, and increased sinkhole activity
(10). During-March of 1980 reductions in the potentiometric surface of the
Floridan aquifer of over 9.1 m (30 ft) and 30.5m(100 ft) were recorded in
nonpumping and pumping wells respectively (A. T. Rutledge, personal communicat-
Another approach to cold protecting plants involves changing the leaf
surface environment. Lindow (8) has found that leaf surface populations of
ice-nucleation-active (INA) bacteria
theirr plants by limiting super coolir
can incite frost damage to corn and
ng of the plant by initiating damaging
Heat Loss from Ferneries
Heat is energy that flows from one place to another by virtue of a
difference of temperature. There are three ways in which heat transfer
ordinarily takes place and, therefore, three factors account for the
majority of the heat loss from leatherleaf ferneries. Heat that flows
through a material is lost by conduction. Heat loss by conduction depends on
three factors: 1) the heat transfer coefficient, U, of the fernery covering,
2) the surface area of the fernery, and 3) the difference between the
temperatures inside and outside the fernery.
Convection, also called infiltration, heat losses are caused by the
circulation of air. These losses can be significant and depend on how open
the fernery is to air movement, the temperature difference between the inside
and outside of the fernery and the amount of wind.
The third type of heat loss is due to radiation of heat to the sky. On
clear winter nights solid objects on earth radiate heat energy into space at
approximately 0.1 calorie/cm2/min or one million BTU/A/hr (9).
Reduction of Heat Loss from Ferneries
I .:II-I Jri .uri UT TU9 -1d- 1T1C di Lr I~d-rrd dIS reue Iaito nedt -.-- --- ___-
In Lfne Turm OT Tog dar~lTIcil or iman-imadae) also reduces raolaaion nead
During the 1980-81 winter ferneries were heated by burning petroleum
derived fuels or applying water. The few ferneries that used heaters were
lined with polyethylene. Conover, et al (1) indicate that heating of fern
nay increase winter yield up to 25%. This winter some fern damage was noted
in ferneries that used heaters. Heaters, of course, are not practical to
cold protect fern in oak hammocks.
As mentioned earlier, most ferneries used water as their heat source.
Heat is added to the system, as water cools to OOC (320F), one BTU* per
degree Fahrenheit per pound of water, due to sensible heat. An additional
144 BTU's per pound is released when OC (32F) water freezes due to the heat
Df fusion. The total heat released depends upon the temperature, volume of
water applied and the amount of water which is converted to ice.
During the winter of 1980-81 a preliminary experiment was initiated to
determine whether fern could be cold protected using about one-half the
recommended amount of water. Nine frost protection nozzles were installed in
place of conventional nozzles in a fernery in northwest Volusia County.
Nozzles were spaced on 9.1 m (30 ft) centers in a 3x3 configuration covering
the area between the southern perimeter of the fernery and a roadway in the
fernery. In addition to this preliminary test a survey was made of many of
the irrigation systems used by growers in Orange, Lake, and Volusia counties
to cold protect fern (Table 1).
Table 1. Irrigation systems used successfully for cold protection of leather-
leaf fern in Orange, Lake, and Volusia counties during the winter of 1980-81.
Type Nozzle Nozzle Pressure Sprinkler Appl Min
No Sprinkler Size Angle at well spacing rate1 temp2
1 SN3 4mm 7 2.8 kg/cm2 9.1m x 9.1m 10.7 mm -13C
(5/32") (40 psi) (30' x 30') (0.42") (90F)
2 SN 4mm 7 2.1 kg/cm2 9.1m x 9.1m 9.1 mm -90 C
(5/32") (30 psi) (30' x 30') (0.36") (160F)
3 SN 4.4mm 120 2.8 kg/cm2 12.2m x 12.2m 7.2 mm -11C
(11/64") (40 psi) (40' x 40') (0.28") (120F)
4 SN 3.2mm 70 2.5 kg/cm2 9.1m x 9.1m 6.3 mm -90 C
(1/8") (35 psi) (30' x 30') (0.25") (15F)
5 SN 4 mm 12 2.8 kg/cm2 12.2m x 12.2m 5.8 mm -11C
(5/32") (40 psi) (40' x 40') (0.23") (120F)
64 SN 2.8mm 11 2.8 kg/cm2 9.1m x 9.1m 5.2 mm -12C
(7/64") (40 psi) (30' x 30') (0.205") (11F)
The efficacy of irrigation for cold protection is dependent on the
distribution of water. Maintenance of an ice and water interface is
essential to maintain the ice-enclosed plant tissue at a temperature of OC
(32F). Water that runs off and does not freeze contributes little heat
energy. The number and type of sprinkler heads, orifice size and design,
operating pressure and rotation rate, all affect water distribution. The
speed of rotation of the sprinklers and the resultant frequency of wetting
of the leaf surface are of great significance in obtaining a maximum
protection from frost. Table 1 shows that leatherleaf fern was successfully
cold protected in the experimental plot with an application rate of about
5.2 mm (0.2")/hr. This application rate is well below conservative published
figures for cold protection of citrus (2). Success of this system was
probably due to the low wind conditions, close sprinkler spacing, high
sprinkler rotation rate and the reduction of heat loss and wind speed due to
the polypropylene shade fabric. Further testing is necessary to determine
if reduced water application rates will provide protection under windy
freeze conditions. Reduced water usage during cold protection periods would
reduce irrigation energy and material requirements, reduce impact on the
Floridan aquifer and reduce adverse effects of copious water applications to
fern and soil.
In addition to the methods for cold protection listed in the first
section, a relatively new method has been under observation. Several species
of bacteria are ice nucleation active (INA) at temperatures slightly below
freezing and initiate formation of ice crystals leading to frost damage.
These bacteria are present on the leaf surfaces of many plants and affect
frost sensitivity of those plants. Methods which control the activity of
these INA bacteria are, therefore, important in diminishing frost and freeze
damage. These methods involve the use of antibiotics, antagonistic bacteria
or bacterial ice nucleation inhibitors (6,7,8). Of the three methods listed
,the easiest to use is a bactericide spray. The following tests were conducted
to determine the potential for controlling INA bacteria on leatherleaf fern ir
Florida. Initial studies did not identify INA bacteria on commercial fern
plantings and, therefore, failed to establish that control of INA bacteria
would diminish the cold damage to fern.
Leatherleaf fern were grown in eight inch pots in a shadehouse until
needed. Four to six plants were chosen for each treatment according to number
of healthy fronds and overall plant appearance. In the first test, six plant!
were treated with a known INA bacterium at the rate of 2 x 107 bacteria per m
sprayed to the point of runoff. Another set of six plants was sprayed with
sterile culture broth of the bacteria adjusted to the same concentration as
the other treatment. Plants were maintained in a greenhouse for one week befl
they were exposed to the frost treatment. The apparatus used for the frost
treatment was constructed by Dr. George Yelenowsky at the USDA station in
Orlando, Florida. Test temperatures were suggested by Dr. Yelenowsky. In oni
experiment plants were exposed to -5C (23F) for 4 hrs while in a second the,
were exposed to -4.4C (24F) for 4 hrs. Four days after this treatment, the
percentage of damaged fronds was recorded for each plant (Table 2). In INA
UdCLer il d LredLtU pldIlLS [il 1U i ur lr+ ri dL -3 1, k. rJ LIit Uallldytd Wda
increased by 300% over the control plants, while for plants treated for
4 hrs at -4.4C (240F), the damage in the presence of the INA bacteria was
increased by 900%. Thus, INA bacteria increase frost or freeze damage on
leatherleaf fern in the same manner as they do on many other crops tested (7).
Table 2. The effect of ice-nucleating active bacteria (INA) on cold damage
to leatherleaf fern.
Duration Mean percentage of
Treatments Temperature (hr) damaged leaves1
INA bacteria -50C (230F) 4 80 a2
Control (broth) -50C (230F) 4 20 b
INA bacteria -4.40C (240F) 4 20 a
Control (broth) -4.40C (240F) 4 2 b
INA bacteria -50C (230F) 2 29 a
Antagonistic bacteria -50C (230F) 2 29 a
INA and antagonistic
bacteria -50C (230F) 2 30 a
Control (broth) -50C (230F) 2 33 a
Streptomycin sulfate3 -50C (230F) 2 22 a
Water -50C (230F) 2 18 a
1Values given are the mean for two tests.
2Means followed by the same letter were not significant at the 5% level using
Duncan's Multiple Range Test.
3Streptomycin sulfate was sprayed at the rate of 200 ppm to the point of runoff.
The second set of tests was performed to determine the potential for use
of antagonistic bacteria on the leatherleaf fern. A bacterium stock
antagonistic to the INA bacteria was obtained and maintained in a freezer
until needed. Four treatments were used, 1. INA bacteria only; 2. antagonistic
bacteria only; 3. both bacteria; and 4. sterile media only. Four plants were
chosen for each treatment and sprayed with the appropriate solution one week
prior to cold treatment. Treatments 1 and 3 were sprayed with hli I I INA l,t (ri
(2 x 107 bacteria/ml) one day before the other treatments were applied. PidniLt
were exposed seven days after application of INA bacteria to -5C (230F) for 2
hrs since damage under these conditions was intermediate. Four days after the
cold treatment plants were rated for percentage of damaged leaves (Table 2).
Treatment 4 (control) incurred the same damage level as the other three
treatments. This test was repeated once with similar results. The use of
antagonistic bacteria in controlling INA bacteria was unsuccessful under these
iII b i- I a i o L uI LutLS a UO CI. Il- i.iuc -pi ay wa: uzocu Lu ucLCI )III1C
effect on INA bacteria which may have naturally occurred on the test fern.
ive plants each were treated with either water or streptomycin sulfate
?00 ppm) sprayed to the point of runoff one week prior to the frost
-eatment at -50C (230F) for 2 hrs. Plants were rated as described earlier.
i the first test less damage occurred on plants sprayed with the
ictericide than those sprayed with water. However, in the second test
iis was reversed and plants sprayed with the bactericide had more damage than
)ntrol plants. On the average no benefit was seen using the bactericide.
ince the response of the plants to the bactericide was so variable, use on
commercial basis would not be advisable.
These tests established several important facts concerning the potential
or cold damage control based on control of INA bacteria. First, INA
icteria do increase the frost damage incurred by fern when applied artifici-
lly, although no evidence has been found to prove that they are involved in
old damage under commercial conditions. Second, application of known
itagonists to fern either in the presence or the absence of INA bacteria did
ot decrease the cold damage to the fern and should not be considered
commercially feasible at this time. Third, the use of bactericide sprays such
s streptomycin sulfate did not consistently decrease the damage from cold and
would not be reliable under field conditions. At present the use of these
methods would not be reliable and cannot replace conventional methods for cold
damage protection in leatherleaf ferneries.
Sincere appreciation is extended to Dr. D. D. Mathur for his assistance
n the frost protection nozzle study and to Dr. G. Yelenowsky for his generous
cooperation and valuable suggestions in performing the INA bacteria tests.
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leatherleaf fern cold protection. Univ. of Fla., Agr. Res. Ctr., Apopka,
Res. Rept. RH-78-6.
Gerber, J. F. and J. D. Martsolf. 1965. Protecting citrus from cold
damage. Univ. of Fla., Agr. Ext. Serv. Circ. 287.
Harrison, D. S. and C. A. Conover. 1970. Irrigation of leatherleaf and
plumosus ferns. IFAS, Univ. of Fla., Agr. Engr. Mimeo Rept. 70-7. p. 5.
Henley, R. W. 1981. Perforated roof liners save heat in shadehouses.
Southern Florist & Nurseryman 18(46):23-24.
5. Henley, R. W., B. Tjia, and L. L. Loadholtz. 1980. Commercial
Leatherleaf Fern Production in Florida. IFAS, Univ. of Fla.
Ornamental Horticulture Report. Coop. Ext. Serv. Bull. 191. p. 21.
6. Lindow, S. E. 1980. New method of frost control through control of
i 1. LII'UVJL .J L. L. 1 I .V n 11I UII ) % UI . JJI %- I JI U LI TV III IU I Il U I u *
A bacterial ice nucleus active in increasing frost injury to corn.
8. Lindow, S. E., D. C. Arny, and C. D. Upper. 1978. Distribution of
ice nucleation-active bacteria on plants in nature. Applied and
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control. Proc. Int. Soc. Citriculture. 1:203-208.
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withdrawals for fernery freeze protection southeast Putnam County,
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Department, Technical Report No. 8.
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