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not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
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Copyright 2005, Board of Trustees, University
COMMON DISEASES OF TROPICAL FOLIAGE PLANTS:
III. Soil-Borne Fungus Diseases1
J. F. Knauss ..... l
IFAS, University of F orida
Apopka, Florida& i0-\E 1IR
ARC-Apopka Research Repo t RH-75-8
The first two articles of this series dealt With the more important opical
foliage plant foliar diseases caused by fungal and bacte ia l n a s.
Although these previously discussed pathogens are eWQjt.a4 -5T ificant in the
Florida foliage plant industry, the fungal pathogens referred to as soil-borne
and causing root, stem and crown rots are by far the most destructive and important.
Severe economic losses caused by soil-borne fungal pathogens are often
experienced by Florida foliage plant growers. These losses probably comprise 25
to 50 percent of the total disease losses resulting from all foliage plant
pathogens. Although these figures are not substantiated by actual data, the author,
after spending nearly seven years in the Florida foliage plant industry, agrees
That disease losses resulting from attacks by these pathogens are high.
This article describes diseases caused by the more important soil-borne
fungal pathogens and includes fungicides found by research to be effective and
nonphytotoxic to foliage plants. The fungicide information, however, must not be
interpreted as a formal recommendation. Rather, foliage plant growers are advised
to consult with their state extension agent as to the legality of employing any
Soil-borne fungal pathogens are capable of attacking seed, seedlings, propagative
cane pieces, rooted and unrooted cuttings and established potted plants. Although
these diseases are usually more severe at particular times of the year, attack by
these fungi may occur year around in Florida because of its subtropical climate.
New foliage growers, especially.those trained in the north, are amazed at the number
and severity of disease problems they must face and overcome to realize a profit.
In addition to Florida's environment, so conducive for plant pathogen multiplication,
other factors that strongly influence disease development are related to many cultural
Originally published as ARC-A Mimeo 72-4. A revised form was published with
photographs in Florists' Review 154(3987), May 2, 1974 and reprinted in Florida
Nurseryman 20(1), January 1975.
methods presently employed.
I. STOCK BED AREA
Without question, the more disease-free the stock plants, the more vigorous
and disease-free plants will be in propagative and finishing areas. In Florida,
stock plants of many plant species are often grown in ground beds of native sandy
soil amended with peat. Effective sterilization of these beds prior to their
planting can be accomplished by chemical fumigation or steam sterilization. These
beds remain clean (free of pathogens) for only a short time before plant pathogens
become reestablished. There is no sense in fooling oneself, maintaining ground beds
in a disease-free state is impossible. The best one can hope for in ground bed
stock production is to maintain a low population of pathogens with a year-round soil
fungicide program. This type of program can be utilized for many foliage plants,
but yields and control of crop quality are usually far less than production in
raised beds under covered structures where sterilized soil mix, improved watering
systems and clean plants are employed. Even with raised bed production, however,
a minimum preventative program of soil fungicide application should be employed
with disease-prone foliage plants (pothos, dieffenbachia, aglaonema, some philodendrons,
maranta and others) to ensure maximum production and profit.
Selection of material to plant in stock beds is difficult because of the lack
of certified clean stock. Cuttings for stock should be chosen from plants known
to be healthy and which are growing under improved cultural conditions. To
minimize the carry-over of soil-borne pathogens, these cuttings should be taken
no less than one foot above the soil surface. Hot-water treatment of hardened
planting material of certain foliage plants (aglaonemas, aloes, caladiums,
dieffenbachias, Fittonia spp., Philodendron spp., Syngonium spp.) has been
employed and may rid the planting stock of soil-borne fungal pathogens such as
Rhizoctonia spp. and Pythium spp. This technique will, however, demand careful
temperature regulation to eliminate possible injury to the plant material.
II. PROPAGATION AREA
Foliage plant propagation by seed, cane or cutting should always be carried
out in raised beds, preferably employing sterilized media. In Florida, unsterilized
domestic or foreign peats are normally employed as the propagative media. Prior
sterilization is probably not so important as it first seems, if the peat is dug
from and old, deep bog and has not been recontaminated with plant pathogens after
digging. Peat from these type of bogs contain few, if any, plant pathogens.
Trouble usually occurs when native peat and/or muck is dug close to the soil surface
* and especially from areas previously cropped to vegetables or ornamental plants.
Peats taken from these areas are usually less desirable horticulturally and also
contain an abundance of pathogens that must be eliminated by fumigation or steam
sterilization prior to use.
After propagation of each crop, plant remains should be removed and new peat
incorporated to replace peat used in the previous propagation. The bed then
should be steam sterilized and leached prior to use. Growers who cannot sterilize
should use all the other procedures mentioned and employ a preventative soil
fungicide program to keep pathogen populations low. These fungicides are normally
applied as a preplant dip to the cuttings and/or drench to the propagative media.
Experience with peat-containing propagative media indicates drench treatments should
be applied prior to planting leafy propagative cuttings and immediately after
sticking nonleafy cuttings, cane sections and seed. Drench rates should be applied
according to the rules outlined at the end of this article. Keep in mind that the
more times a bed is reused without thorough sterilization, the more likely the prospect
of a more difficult-to-control, high pathogen population building up in the propagative
SWhen it is necessary to use unsterilized media, the foliage plant species
should be rotated in propagation areas. Some foliage species that are especially
poor risks to propagate repeatedly in the same media without sterilization are
syngonium nephthytiss), pothos, aglaonema, dieffenbachia, schefflera, neanthe bella
palm and peperomia. One should always follow these crops with a species that is
more disease resistant, one that in the past has given few or no problems during
III. THE FINISHING AREA
Rooted plants should always be potted in a sterilized potting media. Often,
apparently healthy foliage plants progressively deteriorate in the finishing or
holding areas. These plants are either infected at time of potting or were potted
in contaminated media. Even if plant and media are clean at time of potting, the
soil may become recontaminated or plants infected in many ways. Therefore, foliage
plants grown in Florida should receive a broad-spectrum soil fungicide drench soon
after potting. This drench will prevent development of a high pathogen population
in the medium thus allowing root growth and proper establishment. Although one
treatment is usually enough for most potted material, large plants held in the
* nursery for long periods should be retreated once every three months.
Other aids to prevent soil-borne fungal disease development in pots are:
(a) Use of well-aerated, easily drained soil mixes.
(b) Care to not overwater. Water only when needed and then water thoroughly.
(c) Place pots on surfaces that will not restrict drainage from the holes in
the pot. One should never put pots with holes in the bottom directly
on a plastic sheet.
1. Rhizoctonia solani, Rhizoctonia spp.
Susceptible plants: Aglaonemas, aphelandras, ardisias, azaleas, caladiums,
dieffenbachias, ferns, gardenias, Gynura sp., hoyas,
pertusums, marantas, the neanthe bella palm, peperomias,
Philodendron oxycardium, P. selloum, pileas, pothos,
scheffleras, Scindapsus pictus, Syngonium spp. and
Rhizoctonia is active the year around and prefers a warm, not excessively hot,
moist environment. When these conditions exist, growers must be on the lookout
for this pathogen.
Rhizoctonia has a wide host range and attacks all types of plant tissue.
Disease resulting from attack by this pathogen often appears to growers to occur
overnight. Although Rhizoctonia grows rapidly, it does not move that fast. This
impression by growers is probably caused by the pathogen's wide distribution and
its ability to survive conditions unfavorable to its growth and the fact it attacks
a wide variety of foliage plants when conditions become favorable for growth.
Rhizoctonia usually attacks seedlings at or near the soil line causing a pre
or postemergence damping off. On older schefflera seedlings, Rhizoctonia often
causes a reddish-brown constricted lesion at the soil line with healthy tissue
above and below. The fungus also may spread rapidly over the foliar surface of
closely spaced seedlings and cuttings. Aerial infections occur under warm,moist
conditions, especially when seedlings are planted close together. Aerial infections
by this fungus often cause a yellowing and eventual collapse of lower leaves and
stems of closely spaced plants or pots of aglaonemas, dieffenbachias, pothos and
syngoniums. In cases of foliar attack, reduction in watering coupled with wider
plant spacing and use of fans and turbulators to increase air movement among the
plants go a long way in solving the problem.
Normally, identification of Rhizoctonia infections can be made in the green-
house or nursery by the grower. Rhizoctonia produces prominent reddish brown
threads (which are really the body of the fungus) that may be seen on the diseased
tissue. Often these threads can be seen on the soil surface near infected plants.
If Rhizoctonia-infected leaves touch the propagation medium they will usually be
difficult to lift when raised slowly because the threads of Rhizoctonia are attached
to both soil and leaf surfaces. In a sense, these threads act like small ropes
holding the leaf to the propagation media. Again, the threads will be visible.
2. Pythium spp.
Susceptible plants: Aglaonemas, aphelandras, ardisias, caladiums, Christmas
cactus, dieffenbachias, marantas, pertusums, the neanthe
bella palm, peperomias, Philodendron oxycardium, P.
panduraeforme, P. selloum, other philodendrons, pothos,
scheffleras and many others.
In the Florida foliage industry, attacks by this fungus group are most severe
under warm, wet conditions. This temperature effect is somewhat opposite of that
in the north where attacks by species of this group are favored by cool, wet
* conditions. Pythium attacks seed, seedlings, cuttings propagative cane sections,
roots and occasionally stems. Potted plants infected with Pythium usually show a
slight to severe wilt often accompanied by a progressive yellowing of the leaves
from the base of the plant upward. Roots of infected plants will be collapsed
and black in color. Close observation of roots invaded by Pythium will show the
gray to black rot initiating at the root tip and progressing backward. The exterior
of severely rotted roots will sluff off leaving only the inner core giving the
root a hanging-thread appearance. In propagation beds, Pythium alone or in
combination with Rhizoctonia may rot the roots and stems of rooted cuttings causing
their eventual collapse.
Seed and seedling attack by Pythium may be inhibited by wider spacing of seeds
and careful watering. The root rot phase of the disease on rooted cuttings and
potted plants may be inhibited by planting in well-aerated, rapidly drained media.
Care not to overwater aids in Pythium Root Rot control.
Pythium may be spread on contaminated tools, hands, feet, media, flats, pots
or in or on infected plant material. Once established in a growing medium, Pythium
can persist for long periods of time, even in the absence of a susceptible host plant.
3. Phytophthora palmivora, P. parasitica.
Susceptible plants: Aglaonemas, azaleas, caladiums, dieffenbachias, Philodendron
oxycardium, probably other philodendrons, peperomias, others.
Phytophthora is so closely related to Pythium that much of the information
presented previously for Pythiumapplies here as well. As a pathogen group, however,
Phytophthoras are more aggressive when attacking the same host plant and are generally
harder to control than Pythiums. Phytophthora may also attack foliage, often
causing a serious leafspot of Philodendron oxycardium and at times causing a serious
foliar blight of Dieffenbachia species. In contrast to Pythium, Phytophthora has
the ability to attack mature tissue of plants such as Dieffenbachia picta 'Perfection'
causing plant collapse and cane decay. Stem attacks of D. picta 'Perfection" by
Phytophthora are often mistakenly contributed to infection by Erwinia chrysanthemi
because of the close resemblance of resulting disease symptoms. On this host,
positive diagnosis of either pathogen should never be made on symptoms alone and
should be reliant upon actual isolation of the pathogen.
4. Sclerotium rolfsii
Susceptible plants: Caladiums, dieffenbachias, Dracaena godseffiana, the
neanthe bella palm, peperomias, pileas, Philodendron
micans, P. oxycardium, pothos, Scindapsus pictus,
scheffleras, syngoniums and many others.
Sclerotium rolfsii has been reported on a wide variety of agronomic crops.
In Florida, the fungus attacks during the warm to hot, wet periods of the year.
This pathogen is mainly a problem in the south and is not a major concern to
Sclerotium rolfsii is easily recognized by its heavy, white fungus growth on
the soil surface and on the affected plants. Almost always, numerous white to tan
sclerotia about the size and appearance of mustard seeds or small Osmocote granules
can be found where the disease is present. These sclerotia act as resting
structures and allow the fungus to remain in an inactive but living state for long
periods of time. Once established in a propagation bed, S. rolfsii may spread
rapidly and cause rapid and severe losses. Losses from S. rolfsii primarily
occur in the propagation areas, with scattered instances noted in stock and
When a crop in propagation is severely affected by this pathogen, the bed
should be sterilized before reuse. Where impossible, the bed should be cleaned
of all plant residue and foliage plants other than those listed as susceptible to
S. rolfsii should be chosen for propagation. A preplant fungicide drench may
help control the pathogen but lack of phytotoxicity cannot be assured with the
fungicides known to control this pathogen. When centers of S. rolfsii infection
are noted in propagation beds, the diseased plants should be lifted, put into a
bag and destroyed. The infested area plus a 2-foot border should then be drenched
with an effective soil fungicide. After one day, the infested area (2-foot border
not included) should then be removed and discarded.
5. Fusarium moniliforme
Susceptible plants: Dracaena spp.
Little is known of the importance of Fusarium moniliforme in the decays of
unrooted cuttings of Florida foliage plants. Because it can cause a serious
cutting decay of Dracaena deremensis 'Warneckii' and D. marginata it probably also
attacks other dracaenas and the pleomeles, both known to be susceptible to foliar
attack by this pathogen. Understanding the importance of F. moniliforme in the
SFlorida foliage industry depends on future investigations.
FUNGICIDES FOR CONTROL
Several fungicides that are commercially available have been shown to have
excellent to good activity for control of the previously discussed pathogens.
Growers should not, however, think of fungicides as their only line of defense
against soil-borne pathogens but rather incorporate the following fungicide
suggestions with the best available methods of plant culture and employment of
SOIL FUNGICIDES FOR CONTROL OF SOIL-BORNE PATHOGENS
Material Conc./lOO gal. Comments
Banrot 15-25 WP 8 12 oz Good activity, active ingredient
m-thiophanate, also contains
ethazole (Truban or Terrazole)
which is active against Pythium.
Benlate 50 WP
Fermate 76 WP
Terrachlor 75 WP
Banrot 15- 25 WP
Dexon 35 WP
(Truban 30 WP or
Terrazole 35 WP)
Nurelle 7.2 EC
1 1 1/2 lb
3/4 -1 1/2 lb
8 12 oz
8 16 oz
8 12 oz
1 2 pt
Excellent control, must be used in
combination with ethazole or with
Dexon if Pythium or Phytophthora
Good control, may cause stunting
of seedlings and cuttings.
Good control, should be applied
only once a year. May cause
Good activity, active ingredient
ethazole (Truban or Terrazole),
also contains m-thiophanate which
is active against Rhizoctonia
Good control. Also active against
Excellent control of Pythium.
New compound due to be available
in 1976. Excellent control, non-
phytotoxic, systemic. Should be
tried and compared to presently-
(Truban 30 WP or
Terrazole 35 WP)
Nurelle 7.2 EC
8 12 oz
1 2 pt
Moderate to good control.
Excellent control. See above.
Material Conc./lO gal. Comments
Fermate 76 WP 2 3 lb Good control. May cause severe
stunting of seedlings and cuttings.
Terrachlor 75 WP 1 1 1/2 lb Good control. Should be applied
only once a year. May cause
BROAD SPECTRUM DRENCHES
Banrot 15 25 WP 8 12 oz At currently suggested concentrations
will provide control of Pythium,
Rhizoctonia and Fusarium.
Truban 30 WP + 12 oz + 8 oz Best combination for broad spectrum
Benlate 50 WP
control of Pythium, Rhizoctonia,
Fusarium, and Phytophthora.
aIf control of Sclerotium rolfsii is desired also, either Fermate 76 WP (2-3 lb/
100 gal) or Terrachlor 75 wP (1-1 1/2 lb/100 gal) must be used in place of Benlate.
SUGGESTIONS ON DRENCH RATE (VOLUME)
How much to apply to a bed or to pots is often a difficult question to answer.
The following suggested rules, if followed, will provide control with the least
Rate (volume) applied per sq. ft.
Type Unit surface area
Mini-pots and shallow flats 3/4 pint/sq. ft.
Other pots to 4 inches in diameter
and other propagative beds or units
up to 4 inches in depth 1 pint/sq. ft.
Pots > 4 inches in diameter and
propagative beds or units > 4
inches in depth 1 1/2 2 pints/sq. ft.
NOTE: If mixes or soils contain less than 50 per cent peat moss never exceed
application rate of 1 pint/sq. ft.
GENERAL RULES FOR SOIL FUNGICIDE DRENCH APPLICATION
1. Repeat drench applications should be applied no sooner than every 3 months.
2. With all drench applications except Nurelle, come back and lightly rinse
fungicide off foliage after application.
3. Where preventative drench is applied to leafy unrooted cuttings, apply
drench prior to sticking cuttings. Have all workers wear Playtex-type
rubber gloves when sticking cuttings.
To simplify information, trade names of products have been used.
No endorsement of named products is intended, nor is critism
implied of similar products not mentioned. Mention of a chemical
does not imply guarantee of effectiveness or safety, nor that
the chemicals or uses discussed have been registered by appropriate
state and federal agencies.