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GULF COAST RESEARCH & EDUCATION CENTER' Scene
IFAS, UNIVERSITY OF FLORIDA
5007 60th Street East
Bradenton, FL 34203
REC Research Report BRA1988-3 -9
The Control of Fusarium Wilt with The Integrated
Lime (pH), Nitrate-N, Chemotherapy System
Arthur I. Engelhard,S. S. Woltz, and J. P. Jones1
Fusarium wilt is a disease that occurs on many plants especially
ornamentals and vegetables. The pathogen, Fusarium oxysporum (F.O.)
usually has physiologically specialized forms (f.s. or formal specials)
that each cause wilt only in one crop. For example, the carnation wilt
organism is F.O. f.sp. dianthi, the aster f.s. callistephi, the cyclamen
f.s. cyclaminis, the tomato f.s. lycopersici, and the chrysanthemum f.s.
chrysanthemi (although there is a rarely encountered f.s. tracheiphilum
race 1 that causes disease in a few cultivars of chrysanthemum). The
pathogen persists for years in the soil and thus is a constant threat to
future crops after it is present. Severe losses have been experienced by
producers in pot-grown and field grown crops. Many papers have been
written on the partial control of Fusarium wilt but to the author's
knowledge, complete symptom control has not been obtained with any system
other than that described herein. This paper presents details of the
integrated lime (p1l), nitrate-N, chemotherapy control system that was
developed at the Univ. of Florida Research Center at Bradenton and
successfully used commercially in Florida. Some publications by Engelhard
(1,2), Engelhard and Woltz (3,4,5), Jones and Overman (6), Jones and Woltz
(8,9), Woltz and Jones (13) and Holtz and Engelhard (12) support the
statements and conclusions.
The Integrated Lime (pH), Nitrate-N, Chemotherapy System
The method integrates three components which must be used simultaneously
to control disease. The three are (1) p1 control with lime, (2) a
specific form of nitrogen in the fertilizer mix and (3) use of an
effective systemic fungicide. Each of the components gives partial
control and the effects are additive. They are described below.
(1) pH. Research indicates that for best disease control the pH of
the soil should be maintained at least in the range of 6.5 7.0 for the
duration of the crop. The degree of disease control is increased as the
pH is raised. Occasionally when the pH goes higher than 7.0,
micronutrient deficiencies may occur. As the pH drops below the suggested
range, the severity of wilt increases. The pH can be maintained by using
liming materials such as ground limestone, dolomite and hydrated lime.
IProfessor, Plant Pathologist, Professor, Plant Physiologist and
Professor, Plant Pathologist, respectively.
The pH of the soil must be maintained throughout the life of the crop and
must be checked periodically, especially on long season crops.
(2) Specific form of nitrogen. The nitrogen source used should be
all in nitrate form, such as calcium, potassium, or sodium nitrate. If
plants grow poorly in all 103-N determine if 10% ammonium-N gives better
growth while still maintaining good wilt control. Using an ammonium
source such as ammonium nitrate, ammonium sulfate or urea causes a very
significant increase in Fusarium wilt symptoms.
(3) Systemic fungicide. The third component that is needed in the
control system is an effective systemic fungicide. Benomyl 50 H (Benlate)
has been effective when drenched on the soil at a concentration of 120 g
/1OOL (one pound/100 gallons). Approximately 200 ml (6.8 fl. oz.) was
adequate for a 15 cm pot (6-inch) and 50 ml (1.7 fl. oz.) for a 10 cm pot
(4-inch). One application at potting time and a second 10 days later was
effective. No phytotoxicity was observed even at four times this rate on
potted chrysanthemum and King Aster plants. Thiophanate methyl, a
chemical related to benomyl also is effective.
It must be emphasized that this control method will not control Fusarium
wilt effectively unless all three components are used simultaneously. A
susceptible cultivar can be killed by Fusarium wilt even when drenched
with benomyl when the nitrogen source is ammonium nitrate.
HODE OF ACTION
This control method is a disease management system that provides
conditions that are unfavorable for the growth of the Fusarium oxysporum
fungus. A pH in the 6.5-7.0 range or higher coupled with the use of
nitrate nitrogen are conditions which discourage the growth of the wilt
producing fungus. fMinor elements such as zinc, iron and manganese are
less available and their availability decreases as the pH is progressively
raised. The Fusarium oxysporum fungus grows better when luxurious amounts
of the minor elements are supplied. Conversely, reducing the minor
elements starves the fungus. Also dissolved phosphorus and magnesium in
the soil solution are kept at a lower level by elevated soil pH's which
retards the disease production by Fusarium. Therefore, inoculum potential
present in the soil is kept at a lower level. Using a systemic fungicide
that is toxic to the fungus further reduces the level of the disease.
This method was successfully used commercially on chrysanthemum and King
Aster. Using only 2 of the 3 components with carnation was partially
successful in Fusarium wilt control in experimental plots (2). Using
nitrate-N and high pH reduced disease and increased yield significantly on
field grown tomatoes in Florida (6,7,8). Sarhan and Kiraly (10) in
Hungary obtained complete control of Fusarium wilt of tomato with an
integrated nitrate, lime, fungicide regime. It is possible that this
integrated lime (pH), nitrate-N, chemotherapy system, if used in its
entirety throughout the duration of the crop, may effectively control
Fusarium wilt symptoms in any crop infected with a wilt disease caused by
r -. t
This control method is no substitute for good sanitation practices. The
nature of the Fusarium wilt fungus is such that when the disease is
established on a flower farm it is virtually impossible to eradicate it.
Based on information available on several Fusarium wilt diseases, it is
likely that the fungus survives in the soil for many years. It can
potentially survive under greenhouse benches, in field soils, in saran
house post rows, around buildings and even in wood (bench supports). It
was demonstrated by Jones and Holtz (8) at the University of Florida
Research and Education Center, Bradenton, that the tomato Fusarium wilt
fungus can live in wooden tomato stakes and can be spread to non-infested
fields on the stakes. The wilt fungi can grow in nutrient solutions in
hoses and in watering systems. It can also be spread by wind, running
water, and soil on equipment, shoes and soil under fingernails. It can be
spread by tools used in taking cuttings and by infected cuttings. The use
of "home-grown" or non-indexed cuttings may provide a source of the
fungus, even though the cuttings themselves do not show visible symptoms.
The integrated system method should be used in addition to all the good
sanitation and fumigation measures that are constantly needed to control
the spread of Fusarium wilt.
Fusarium wilt should be prevented from occurring rather than treating the
problem after it exists. Methods of preventing or controlling Fusarium
1. Use as resistant a cultivar for specific needs as possible.
Remember, however, that the fungus can live in cultivars showing
few or no outward symptoms.
2. Fusarium wilt can be carried in chrysanthemum cuttings. Obtain
cuttings from sources with up-to-date culture-indexed programs
which include screening for Fusarium wilt (Strider and Jones,
3. Plant only in disease free soil or potting mixtures. Steam
sterilize soil. Use steam at 130oF for 30 minutes or methyl
bromide at 20/100 ft2,
4. If Fusarium wilt is present:
a. Sterilize hands, hoses, "spaghetti" watering systems,
benches and all other equipment that comes in contact with
the plants or pots. Flush out hoses and watering systems
with diluted (10% chlorox) sodium hypochlorite, LF 10, or
b. Keep feet off benches, keep fingers and tools out of pots
of plants (unless first dipped in a disinfectant).
c. Carefully remove infected plants and/or containers by
placing in a plastic bag where they are growing and remove
from the growing site. Never dump on the growing site as
the soil underneath will probably stay infested for years.
Haul to a dump at least one mile away and bury to prevent
spread of the spores. Do not spread soil from the infested
location to surrounding areas.
d. Spot fumigate infested sites immediately.
Symptoms and Diagnosis
Fusarium wilt of chrysanthemum is frequently difficult to diagnose because
of the variability of the syndrome of symptoms on the various cultivars.
The symptoms may resemble those caused by Pythium root rot, Fusarium stem
rot, nutritional deficiencies or excess water.
Disease development depends on the chrysanthemum cultivar and
environmental factors such as temperature (minimum temperature about 720F
day and night), nitrogen nutrition and soil reaction. When conditions for
disease development are optimum, the first symptom is chlorosis or
yellowing of one or more leaves on one side of the stem tip. There may be
a slight to pronounced cupping and curvature of the chlorotic leaves. The
stem often curves toward the affected side of the plant, particularly if
one side of the vascular system happens to be more affected than the
other. This is common on young, rapidly growing, susceptible cultivars.
As the disease progresses, chlorosis of the affected leaves becomes more
general and severely affected leaves wilt. Wilting leaves occur initially
on the most severely affected side of the plant, but as disease progresses
the entire plant wilts and dies.
Symptoms on the more resistant cultivars include leaf chlorosis, stem
necrosis, stunting of the leaves and reduced rate of plant growth. These
symptoms may be so mild that they resemble a nutritional disorder or so
severe that after extended periods of leaf chlorosis stem necrosis and
death of the plant follow. Black necrosis of the stem sometimes occurs.
It may extend from the roots into the upper part of the stem. In some
instances, this black necrosis occurs only in the upper part of the stem
and has no externally visible connection with the base or tip of the
plant. This black streak symptom may be confused with Pythium root and
Vascular discoloration always occurs in the stems when there are leaf
symptoms. It also occurs in the leaves of some cultivars. In the stem,
various intensities of brown to reddish brown discoloration are associated
with the portion of the vascular system leading to affected leaves.
Externally visible vascular discoloration in leaf veins occurs on some
cultivars but is uncommon. On cvs. Yellow Delaware and Delaware, vascular
discoloration of leaf veins is prominent and one of the earliest symptoms.
In greenhouse experiments, leaf symptoms showed one week after inoculation
on a very susceptible cultivar like Yellow Delaware but not until 5 weeks
on a more resistant one like Bluechip when both were grown under identical
conditions. Yellow Delaware plants died in 4 weeks while Dluechip had
mild symptoms 8 weeks after the initial inoculation.
On carnation plants leaves become chlorotic and then necrotic. Vascular
discoloration occurs first in the side of the stem associated with the
initial infection. The non-infected side of the stem continues to grow
while the vascularly affected side does not, resulting in the formation of
the familiar shepherd's crook on the terminal of the affected stem.
Leaf wilt on one side of the plant followed by a black streak up the stem
occur on King Aster. Leaf chlorosis and general wilt occur soon after
visible symptoms appear on this very susceptible crop plant.
Chlorosis of leaves, wilt and vascular discoloration are symptoms common
to most plants infected with Fusarium wilt.
1. Engelhard, A. IU. 1975. Aster Fusarium wilt: Complete symptom
control with an integrated fungicide-N03-pH control system. Proc.
Amer. Phytopath. Soc. 2:62.
2. Engelhard, A. U. 1979. Control of Fusarium wilt of carnation with
an integrated nitrate-nitrogen and systemic fungicide control
program. Phytopathology 69:1027.
3. Engelhard, A. H. and S. S. Woltz. 1971. Fusarium wilt of
chrysanthemum: Symptomatology and cultivar reactions. Fla. State
Hort. Soc. Proc. 84:351-354.
4. Engelhard, A. H. and S. S. Holtz. 1972. Complete control of
Fusarium wilt of chrysanthemum with chemotherapeutants combined with
a high lime and nitrate-nitrogen culture regime. Phytopathology
5. Engelhard, A. U. and S. S. Holtz. 1973. Fusarium wilt of
chrysanthemum: Complete control of symptoms with an integrated
fungicide-lime-nitrate regime. Phytopathology 63:1255-1259.
6. Jones, J. P. and A. J. Overman. 1971. Control of Fusarium wilt of
tomato with lime and soil fumigants. Phytopathology 61:1415-1417.
7. Jones, J. P. and A. J. Overman. 1985. Management of Fusarium wilt,
Fusarium crown rot, Verticillium wilt (race 2), southern blight and
root-knot of tomato on fine sandy soils. Proc. Fla. State Hort. Soc.
8. Jones, J. P. and S. S. Woltz. 1968. Field control of Fusarium wilt
(race 2) of tomato by liming and stake disinfestation. Proc Fla.
State Hort. Soc. 81:187-191.
9. Jones, J. P. and S. S. Woltz. 1970. Fusarium wilt of tomato:
Interaction of soil-liming and micronutrient amendments on disease
development. Phytopathology 60:812-313.
10. Sarhan, A. R. T. and Z. Kiraly. 1931. Control of Fusarium wilt of
tomato with an integrated nitrate-lime-fungicide regime. Acta
Phytdpath. Acad. Scient. Hungaricae 16(1-2):9-14.
11. Strider, D. L. and R. K. Jones. 1985. Fusarium-free cuttings are
available. N. C. Flower Growers Bulletin 29(4):5-7.
12. Woltz, S. S. and A. W. Engelhard. 1973. Fusarium wilt of
chrysanthemum: effect of nitrogen source and lime on disease
development. Phytopathology 63:155-157.
13. Woltz, S. S. and J. P. Jones. 1968. Hicronutrient effects on the in
vitro growth and pathogenicity of Fusarium oxysporum f. sp.
lycopersici. Phytopathology 58:336-338.