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Copyright 2005, Board of Trustees, University
Update on Leatherleaf Fern Wilt
C. A. Conover, R. T. Poole and L. L. Loadholtz :
Agricultural Research Center Apopka
University of Florida
ARC-A Research Report RH-79-1
Research conducted to date on leatherleaf fern wilt has not provided
any final answer to the question, "What causes wilt"? However, research
data collected from cooperating fern producers during 1978 has provided
useful information that can be used by the fern industry and as the basis
for specific research. The results of an experiment where fern was
collected from five Volusia County fern producers and compared with ARC-
Apopka fern are described below. The test was started on July 6th, and
fern was collected every 2 weeks through November 8th, 1978.
An attempt was made to select 5 producers with fern reported to have
varying problems with wilt, from none to severe. Cut ferns were held in
deionized water under 75 ft-c for up to 14 days. Wilted fronds were
removed daily and the number of days to wilt recorded. Many comparisons
can be made with the large volume of data accumulated, but only those
considered most relevant are discussed.
Growers have reported that wilt becomes a problem in July and continues
until the cool nights of fall occur. Data in Table 1, however, indicates
that some other factor depressed the severity of fern wilt in our hottest
An attempt to correlate information in Table 1 with temperatures
recorded in the ferneries was unsuccessful, since maximum temperatures
remained high from July 20 through October 12. However, very high rainfall
occurred in the month of July while almost none occurred in early August,
and these data correlate well with severe wilt in July and low levels in
Table 1. Influence of harvest date on number of Leatherleaf fronds
wilted after 3, 6, 9 and 12 days.
Number wilted fronds*
Harvest Date 3 6 9 12
July 6 5 8 11 13
July 20 11 18 23 24
August 3 7 13 21 24
August 17 2 6 10 20
August 31 2 2 11 19
September 14 5 11 15 19
September 28 3 11 22 26
October 12 4 13 18 23
October 26 1 1 4 7
November 8 0 1 6 9
Average of fern from all sources
- out of 30 fronds.
When a wilting average for all weeks was developed for all six sources
of leatherleaf fern, the data in Table 2 was obtained.
Table 2. Influence of source on number of leatherleaf fronds wilted
after 3, 6, 9 and 12 days.
Number of wilted fronds*
Source 3 6 9 12
A 9 19 23 26
B 1 3 7 16
C 4 6 12 18
D 3 7 13 18
E 4 10 18 23
F 1 4 7 10
*Number wilted fronds out of 30.
Source F is Agricultural Research Center-Apopka fern, and we know the
most about this source. However, we should mention that in two previous
years we had not been able to obtain any wilted fronds in a two week
period. Thus, these results represented a deterioration in the quality
of this Research Center's fern.
Originally, we believed that high fertilizer levels could be causing
fern wilt. However, a comparison of source B's fern (900 lbs N/A/yr) with
this Research Center's fern (F) which received 450 lbs N/A/yr indicated
this was probably not a factor.
During September in conversations with producers the subject of
fertilizer sources and ratios was discussed. Based on information supplied
by producers, the comparison of fertilizer source (specifically nitrogen
source) with percent wilted fronds was highly correlated. Specifically,
producers who used fertilizer sources composed almost exclusively of Urea
and Ammonium (Sources A and E) had the most severe wilt problem, while those
using 25% nitrate nitrogen (Sources B and F) had the least. Fern sources C
and D were intermediate, and there was an indication that they used some
nitrate nitrogen, but probably less than 15%. These data indicate that there
is a possibility that nitrogen source is very important to the fern wilt
problem. One additional point worth mentioning is that the fertilizer source
-*: at Agricultural Research Center-Apopk- prior to 1978 was 50% Nitrate 50%
Ammonium, and was changed in February 1978 to 25% Nitrate 25% Ammonium -
Fern tissue samples taken monthly from the various producers (4 sets of
samples) during the term of this research do not show major differences in
macronutrients. Although this may be difficult to understand, it has been
consistent. The only difference observed in tissue content of good versus
wilt prone fern has been with micronutrient levels. Generally, fern with
the highest wilting percentage has been high in manganese and zinc. What
this means is unclear at this time, but previous research indicated that
relatively low levels of micronutrients were capable of decreasing yields.
In addition to the research described, considerable other research was
conducted during 1978. Dr. Marousky at the AREC-Bradenton worked on post-
harvest factors such as holding solutions, stem cutting and temperature, and
found that although he could somewhat delay wilting (1 to 2 days) he could
not stop it. Dr. Sheehan and Dr. Nell from the Ornamental Horticulture
Department conducted dye tests to determine if there were stem obstructions
to water uptake, but found that solutions moved equally well in fern that
wilted quickly and fern that did not. They also examined both wilted and
non-wilted fern stems under an electron microscope and could not observe
any stem blockage. Dr. Knauss at the ARC-Apopka examined both wilted and
non-wilted fern stems on several occasions and could not find any disease
organism present that could account for wilting. Dr. Hamlen examined the
level of nematode infestation between fern that wilted and did not, but
obtained no correlation whatever.
As a sideline to the collection of fern from various sources, we
attempted to retard wilting of fern that we obtained from the poorest source.
We used several compounds that either closed stomates or coated foliage,
Sbutnone provided more than 1 to 2 days extra shelf life. The best material
we used was Vapor Guard at a rate of one part to 50 parts water as a dip.
We do not, however, suggest this as standard practice.
In summary, research conducted during 1978 indicates that the wilt
problem is probably not due to a new pathogen or pest, or to stem blockage.
Rather, indications are that the basic physiology of the fern has been
altered to produce weak stems with large thin walled cells. Based on what is
now known we believe nutrition and watering are factors to be considered.
Thus, the suggestions that follow should be beneficial in reducing wilt
problems in leatherleaf ferneries during 1979.
1. Fertilizer Source Use a fertilizer source (whether liquid or dry)
that provides 40 to 60 percent of the nitrogen in the nitrate form.
2. Fertilizer Ratio Use a 2-1-2 or 4-1-4 ratio since leatherleaf fern
does need phosphorus. Use a 1-0-1 ratio only if a soil test indicates
that you have high phosphorus.
3. Fertilizer Level The annual fertilizer rate depends on whether water
is used for freeze control and the age of the fern, as both these
influence the requirement. The suggested range for fern is as follows:
400-600 lbs N/A/yr
200-300 lbs P205/A/yr
400-600 Ibs K20/A/yr
The lower rates are for established fern that is not sprinkler
irrigated for frost control, while the higher rate is for young fern
that is sprinkler irrigated for frost control.
4. Micronutrients Research at the ARC-Apopka has shown a yield decrease
of 10 to 25% over a period of a year when a single micronutrient
application was made. Table 3 shows comparisons
presently used in the leatherleaf fern industry.
Table 3. Comparison of micronutrient levels obtained
sources when 500 lbs N/A/yr is applied from
with some fertilizers
from several fertilizer
a 2-1-2 ratio fertilizer.
Element A B C D E
Magnesium Mg 60.00 112.5 150.00 14.8 0.0
Manganese Mn 15.00 10.6 7.50 1.5 35.5
Copper Cu 1.50 12.5 1.25 0.4 0.0
Zinc Zn 4.50 12.5 3.75 1.8 1.0
Iron Fe 24.00 43.7 6.25 2.1 0.0
Boron B 0.15 2.0 1.25 0.1 5.0
Molybdenum Mo 0.01 0.0 0.06 0.0 0.0
This level caused a 10% yield
reduction over a check which did not receive
Source A was the rate that provided a 10% yield decrease. Although
direct comparisons are not possible, it is possible that source B could
easily decrease yield by 10% or more, and source C may also present a
problem. Source E is excessively high in boron and the manganese rate might
also be high. Source D is probably acceptable and may even be slightly low.
However, without extensive research none of these points can be proven. ..
As a suggestion, any fertilizer with an analysis close to 10% nitrogen
(8 to 12%) should contain the following ranges if approximately 500 lb N/A
Magnesium Mg 0.10 to .30
Manganese Mn 0.03 to 0.06
Copper Cu 0.008 to 0.015
Iron Fe 0.035 to 0.07
Zinc Zn 0.020 to 0.04
Boron B 0.016 to 0.02
5. Soil pH is important because it controls availability of macro and
micronutrients; especially the conversion of ammonical forms of nitrogen
to nitrates. The pH range presently suggested is between 5.5 and 6.0,
but our research has shown yield decreases at 6.0 and above. Therefore,
based on present information, we suggest the pH be maintained from 5.5
to about 5.8.
6. Watering Based on observation, we feel that leatherleaf fern is often
overwatered, and this may have an effect on fern wilt. In our experience
we have found that 1 to 2 inches of water a week is sufficient during
warm seasons and 1/2 1 inch during winter months.