HISTORIC NOTE


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not reflect current scientific knowledge
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Copyright 2005, Board of Trustees, University
of Florida









SUGGESTIONS FOR THE CONTROL OF SOIL-BORNE
FUNGAL PATHOGENS OF FOLIAGE PLANTS

J. F. Knauss
Agricultural Research Center Apopka (ARC-A)
Apopka
ARC-A Mimeo 72-4


The following information is an extension of ARC-A Mimeo 71-2 and is

intended to serve as a guide for the control of soil-borne fungal patIhgens-

of foliage plants. The chemical control measures sigge sitfust i '

misinterpreted as a formal recommendation nor is the'use of trade ame
AUGU |
intended to discriminate against products sold by other producers which

might be just as effective or may be the same but sold under a jffe~i* 0orida

trade name. All chemicals and rates mentioned are suggest'eT~ or media

consisting totally or largely of peat and may not be safe in other media

types.


INTRODUCTION

Severe economic disease losses caused by soil-borne fungi are experienced

every year by foliage plant growers. Losses resulting from attacks by soil-

borne fungal pathogens have been estimated to comprise 25 50% of the total

disease loss resulting from attacks by all foliage plant pathogens. Although

these estimates are not verified as fact, the author after 3- years of

observation of Florida foliage plant production, agrees losses resulting

from attacks by soil-borne fungi are high indeed. For the purpose of this

mimeo we will restrict the subsequent discussion to those soil-borne fungal

pathogens which cause the majority of disease, i.e., species of Pythium,

Phytophthora, Rhizoctonia and Sclerotium rolfsii.













SOIL-BORNE PATHOGENS, INFORMATION RELATIVE TO THEIR CONTROL

These pathogens are capable of attacking all manner of plant material,

i.e., seeds, seedlings, cane pieces, rooted and unrooted cuttings, and small

and large potted plants. Although disease is more severe at particular times

of the year, attack may occur almost year-round with most of these pathogens

because of Florida's sub-tropical climate. Because of this, many ornamental

growers who are growing in Florida for the first time are amazed at the

number and severity of disease problems they must face and overcome in

order to realize a profit. An environment ideal for disease development is

truly the main reason Florida is such a haven for plant disease.

In conjunction with an environment conducive to disease development are

several other reasons for the severe soil-borne diseases experienced by

Florida foliage growers. These are listed in the following discussion

according to the growing area involved:

1. Stock Bed Area

In the Florida foliage industry most stock areas have been prepared as

ground beds of native soil in open slat sheds. This soil is usually

amended with peat or some other suitable organic material. Effective

sterilization of these beds, prior to planting, may be accomplished by

chemical fumigation or steam sterilization. The "clean" nature (freedom

from pathogens) of these ground beds, however, usually lasts only a short

time. This occurs because of the relative ease by which pathogens are

reintroduced into the clean area on diseased or infested planting material

or by spread from infested areas by normal foliage plant cultural methods.

There is no sense fooling ourselves, maintaining ground beds in a disease-

free state is an impossible task. The best one can hope for in ground bed









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stock production is to maintain a low population of pathogens by utilizing

a year-round soil fungicide program directed at keeping the major pathogens

under control. This can be accomplished for many foliage crops but the over-

all profit realized probably is far less when compared to raised bed production

in covered structures where clean soil mix and plant material are employed.

Even with raised beds, however, a minimum preventative program of soil

fungicide application will have to be employed with the more disease-prone

crops (pothos, dieffenbachia, aglaonema, some philodendrons, maranta, and

others) to insure maximum production and profit.

2. Propagation Area

Foliage plant propagation by seed, cane or cutting is ordinarily done

in raised beds consisting totally or largely of domestic or foreign peat.

Often the media employed in these beds are not sterilized prior to propagation.

This may not be as important as it first seems, however, if the peat is dug

from an old, deep bog. Trouble with propagation peat usually occurs when

a native peat or muck is used which was dug from an area previously cropped

to vegetables or ornamental plants. Peat taken from this type of area

often contains an abundance of pathogens that must be eliminated by fumigation

or steam sterilization in order to produce quality foliage plants.

After propagation of the initial crop in the new bed, the bed should

be worked up, the plant remains (roots, leaves, stems, etc.) pulled out and

new peat mixed in to replace the peat used-up in propagation of the previous

crop. The bed should then be steam sterilized to eliminate all remaining

pathogens. After sterilization, the bed must be leached thoroughly.

Growers who do not sterilize their propagation beds prior to re-use, should

use the other pre-mentioned procedures (other than sterilization) and employ

a preventative soil fungicide program to keep the pathogen population low.










These fungicides are normally applied as a plant dip to the propagative

material prior to sticking or as a drench to the propagative media.

Experience with peat media indicates that drench treatments to the bed

for maximum effectiveness should be applied just prior to sticking leafy

propagative units. The drench may, however, be applied immediately after

sticking non-leafy cuttings, cane sections or seeds. In both cases,

application is at a rate of 1 quart per square foot of propagation area.

Keep in mind that the more times one reuses a propagation bed without a

thorough sterilization, the more likely is the prospect of building up a

high pathogen population which will be more difficult to control.

When reusing propagation areas attempt, whenever possible, to rotate

the foliage species after each propagation. Foliage species that are

especially poor risks to repeatedly propagate in the same media without

media sterilization are syngonium nephthytiss), pothos, aglaonema, dieffenbachia,

neanthe bella palm and peperomia. Always follow these with a foliage

species which is more disease resistant, i.e., one which in your past

experience has given little or no problems.

3. Finishing Area Pots, Combinations, etc.

Often after potting, apparently healthy foliage plants progressively

deteriorate in the holding or finishing area. Plants that respond in this

manner were probably infected at time of potting or were potted in pathogen-

infested media. Even if the plant and media are clean when potted, the

soil may become recontaminated or the plant may become infected in several

different ways. Because the chances of media recontamination are good under

present growing methods, a broad-spectrum soil fungicide drench (at the rate

of 1 pint/6 inch pot) should be applied soon after potting. This drench








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will prevent a high pathogen population in the media thus allowing root

growth and proper establishment of the potted foliage plantss. The fungicide

drench will also protect against recontamination of clean soil from contaminated

sources. Although one treatment is usually enough for most potted material,

large potted plants which will be held in the nursery for a long period of

time should probably be retreated once every 4 months. The following combi-

nations appear to give broad spectrum activity: Truban Benlate, Truban -

Terraclor, Dexon Benlate, Dexon Terraclor, with Truban and Terraclor

used at 12 oz. and Benlate and Dexon used at 1 Ib each per 100 gal water.

Other aids in preventing soil-borne fungal disease development in pots

are:

1. Use well-aerated, easily drained soil mixes.

2. Take care not to overwater, water only when needed and then thoroughly.

3. Place pots in a manner which will allow unrestricted drainage from

the holes in the pot. Never put pots with holes in the bottom

directly on a plastic sheet.



THE MAJOR PATHOGENS

Pythium species

This fungus group produces disease year round but is most severe in the

wet, warm months. Pythium attacks seeds, seedlings, cuttings, cane, roots

and occasionally stems. Seed and seedling attack may be inhibited when they

are not planted close or kept excessively wet. Pythium Root Rot may be

inhibited by planting in well-aerated, rapidly drained media. Care not to

overwater also aids in root rot control. This pathogen may be spread on

contaminated tools, hands, feet, media, flats, pots or in or on infected








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plant material. Once established in the media, Pythium can persist for long

periods of time, even in the absence of a susceptible plant. Foliage plants

which are particularly susceptible to this fungus group and chemicals which

may be used for control will be listed later.



Phytophthora species


The information presented for Pythium applies in large part also for

this fungus group. Although closely related to Pythium, Phytophthora is

more difficult to control. It also attacks the leaves and has been observed

to produce severe foliage disease on Philodendron oxycardium and Dieffenbachia

amoena. Another feature of this group which is different from Pythium is

its ability to attack mature plant tissue often causing severe stem and

cane decays of fully matured plant tissue. As with Pythium, susceptible

foliage species and chemicals for control will be listed later.



Sclerotium rolfsii


Attacks by this fungus are generally restricted to the warm to hot

portions of the year, with the most severe disease losses occurring when

wet and humid conditions exist for long periods of time. This fungus is

easily recognized by its heavy, weft-like white growth on the soil surface

and the affected plants. Almost always, numerous light tan sclerotia about

the size and appearance of mustard seeds or small osmocote granules are found

to be present. These sclerotia act as resting structures and allow the fungus

to remain in an inactive but living state from one crop to another and for







-7-

much longer periods of time. Once established in a propagation bed, S. rolfsii

may spread rapidly and cause rapid and severe losses if left unchecked. A

wide range of plants are attacked by this fungus with losses occurring

primarily in propagation areas but with scattered instances noted in stock

and finishing areas.

When a crop in propagation is severely diseased by this pathogen, the

bed should be sterilized before reuse. If this is impossible, clean the

bed of all plant residue and propagate a foliage plant known to be resistant

to S. rolfsii. A preplant drench with Terraclor, Fermate or Demosah may help

but safety to the propagative material cannot always be assured with any of

these fungicides. When centers of S. rolfsii infection are noted in a

propagative bed, the diseased plants should be removed carefully and the

infested area plus a 2 foot border drenched with one of the previously-

mentioned fungicides. The infested soil (2 ft border not included) should

then be carefully removed after being allowed to set for 1 day. As stated

for the previous pathogens, a list of susceptible plants and chemicals for

control will be listed later.



Rhizoctonia species


Of all the soil-borne fungal pathogens that attack foliage plants, this

group appears to be the most active on a year-round basis. It has caused

untold losses in the propagation and finishing of foliage plants. Rhizoctonia

prefers a warm, not excessively hot, moist environment. This corresponds

in the Florida foliage industry to the periods of middle and late spring and

fall. Although this generalization is normally true, the winter of 1971-72









-8-

was an exception and had periodic warm and moist periods. During these

periods Rhizoctonia was particularly active and many growers were unprepared

to combat the problem. Disease resulting from attack by this pathogen often

appears to growers to occur overnight. Although Rhizoctonia grows rapidly,

it does not move quite that fast. This impression among growers is probably

caused by the fungus' wide occurrence throughout the growing areas, its

ability to survive during weather unfavorable to its growth, and its ability

to attack rapidly such a wide variety of foliage plants.

Rhizoctonia is easily recognized by the prominent red-brown threads it

produces. These threads may often be seen when affected plant material is

examined closely. Often these threads are seen on the soil surface in the

diseased area. If Rhizoctonia-infected leaves touch the media surface they

will usually be difficult to lift, if raised slowly, because the threads

are attached to both the soil and leaf surface. In a sense, these threads

act like small ropes holding the leaf to the media surface. Again the

threads will be visible.

When foliar attack of foliage plants occurs, reduction in watering,

wider spacing to allow better air movement among plants, increased air

movement produced by fans or turbulators and foliar applications of Benlate

or Daconil will control the pathogen.

In all types of production, this pathogen as with the previously-

mentioned pathogens, is best controlled when clean plants, soil and pots

are utilized. With problem crops, however, most effective control is

usually achieved when a preventative fungicide drench is employed just

prior to or just after sticking the propagative material and soon after

potting. Of the fungicides tested thus far as a soil drench, Benlate has

generally been the most effective and definitely the safest. Benlate may

be applied several times in the same area or to the same pot several times








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a year. This may not be the case with the other fungicides to be listed

later as they should not ordinarily be used more than once a year to the

same media or pot.



FOLIAGE PLANTS PARTICULARLY SUSCEPTIBLE TO THE
MAJOR SOIL-BORNE FUNGAL PATHOGENS


In the following, the major pathogen will be listed. Underneath each

list will be found foliage species and type of tissue which the author has

found to be particularly susceptible to the pathogen. Foliage growers are

encouraged to utilize the lists as a guide to the problems they may face

and to take preventative action to keep the soil-borne fungal pathogens

under control.



Pythium


Plant
Attacked

African violet

Aglaonema spp.

Aphelandra spp.

Ardisia sp.

Caladium sp.

christmas cactus

Dieffenbachia spp.

Maranta spp.

Monstera deliciosa (P. pertusum)


Tissue
Attacked

roots, stems

roots, stems

roots, stems

seeds, seedlings, roots

roots

roots, stems

roots, canes, stems

roots

roots, stems







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Pythium cont'd


Plant
Attacked

neanthe bella palm

Peperomia spp.

Philodendron panduraeforme

P. selloum

pothos

schefflera


Tissue
Attacked


roots

roots, stems

roots

roots, stems

roots, stems

roots, seedlings


Phytophthora


Plant
Attacked

African violet

Aglaonema spp.

azalea

Caladium spp.

Dieffenbachia spp.

Philodendron oxycardium


Tissue
Attacked

roots, stems, leaves

roots, stems

roots, stems

tubers, roots

roots, canes, stems

leaves, stems


Sclerotium rolfsii


Plant
Attacked

Caladium spp.

Dieffenbachia spp.

Dracaena godseffiana


Ti ssue
Attacked

tubers, petioles

canes

cuttings, stems







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Sclerotium rolfsii cont'd




Plant
Attacked

neanthe bella palm

Peperomia spp.

Pilea sp.

Philodendron micans

Philodendron oxycardium

pothos

Scindapsus pictus

schefflera

Syngonium spp.


Tissue
Attacked

seedlings

cuttings, stems

cuttings, stems

cuttings, stems

cuttings, stems

cuttings, stems, stock plants

cuttings, stems

seedlings, stems

seedlings, cuttings


Rhizoctonia spp.


Plant
Attacked

African violet

Aglaonema spp.

Aphelandra spp.

Ardisia sp.

azalea

Caladium spp.

Dieffenbachia spp.

ferns

Gardenia spp.

Hoya spp.

Monstera deliciosa (P. pertusum)


Tissue
Attacked

stems, leaves

stems, leaves, roots

seedlings

cuttings, stems, leaves

cuttings, stems, leaves

tubers, roots, leaves

canes, cuttings, roots, stems

foliage, roots

cuttings, leaves

cuttings, leaves

roots, seedlings, leaves








-12,


Rhizoctonia spp. cont'd


Plant
Attacked

neanthe bella palm

Peperomia spp.

Philodendron oxycardium

Philodendron selloum

Pilea spp.

pothos

Purple Passion (Gynura sp.)

schefflera

Scindapsus pictus

Syngonium spp.


Tissue
Attacked


seedlings

stems, cuttings

roots, cuttings, stems

seedlings, roots, stems

seedlings

cuttings, roots, leaves, stems

cuttings, leaves

seedlings, stems, roots

cuttings, stems

cuttings, leaves


Soil Fungicides Suggested for Pythium Control


Truban 30 WP 8-12 oz/100 gal

Very effective; effective often for 8-12 weeks (long lasting); safe

for use on foliage plants at suggested concentration. Application may

be repeated every 3 months in media consisting totally or largely of

peat; should not be applied more than twice a year to sandy, ground

beds; may be mixed with Benlate or Terraclor.







:-13-

Soil Fungicides Suggested for.Pythium Control Cont'd


Dexon 35 WP 1.0 lb/l00 gal

Effective; effectiveness may last only 1 month where heavy watering

occurs; light sensitive; may injure plants if used more than 3 times

a year in same soil; tendency to injure plants in sandy soils, even

with only one application; compliments Truban in a control program

because of activity against Pythium and fact that recent research

indicates considerable activity against the bacterial genus, Erwinia.

This genus (Erwinia) commonly causes many propagative rots of foliage

plants. Dexon may be mixed with Terraclor or Benlate.



Soil Fungicides Suggested for Rhizoctonia Control


Benlate 50 WP 1.0 lb (0.5 lb as foliar spray)

Most effective chemical tested; no injury as drench on cuttings of Hoya,

Syngonium, Purple Passion or seedlings of schefflera; expensive but

should be part of all Rhizoctonia control programs.



Terraclor 75 WP 1.0 Ib

Very effective; slight injury to cuttings of Syngonium and Purple

Passion and to seedlings of schefflera; moderate to severe injury to

cuttings of Hoya; Use only once a year in same soil, alternate with

other chemicals.







-14,

Soil Fungicides Suggested for Rhizoctonia Control Cont'd


Daconil 75 WP 1.5 Ib

Effective but when applied as drench moderately to severely injured all

plants tested; as foliar spray effective and safe for control of foliar

Rhizoctonia.



Demosan 65 WP 1.0-1.5 lb

Slightly to moderately effective; slight to moderate injury on Syngonium,

Purple Passion and Hoya. Moderate injury on seedlings of schefflera.



Fermate 76 WP 2.0-3.0 lb

Effective; severe injury to s.hefflera seedlings; initially slight to

moderate injury to cuttings of Purple Passion but disappearing after

rooting and extended watering.



Soil Fungicides Suggested for S. rolfsii Control



Terraclor 75 WP 1.0 lb

Most effective and long lasting chemical tested. Slight phytotoxicity

to seedlings of schefflera and cuttings of Syngonium and P. oxycardium;

slight to moderate phytotoxicity to rooted and unrooted cuttings of

Peperomia. Use only once a year in the same soil, alternate with another

chemical.







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Soil Fungicides Suggested for S. rolfsii Control Cont'd


Demosan 65 WP 1.0 lb

Effective for approximately one month but effect decreases with

prolonged watering; slight phytotoxicity to cuttings of Syngonium;

slight to moderate phytotoxicity to cuttings of Peperomia and seed-

lings of schefflera.



Fermate 76 WP 2.0-3.0 lb

Effective and long lasting; severe phytotoxicity to seedlings of

schefflera and cuttings of Syngonium; slight to moderate phytotoxicity

to cuttings of Peperomia.



Soil Fungicides Suggested for Phytophthora Control


To date little information is available on the relative effectiveness

of soil fungicides for control of this pathogen on foliage plants.

Fungicides which have given an indication of some degree of control

when used as a drench are Truban 30 WP (12 oz), Dexon 35 WP (1 lb)

and Dithane M-45 (2 lb). Truban and Dexon appear to be safe on most

plants, while M-45 will cause phytotoxicity to dieffenbachia. For

foliar infections Daconil WP (1.5 lb) and Dithane M-45 (1.5 lb)

applied as foliar sprays appear to provide the best control.