Common fungal root rot diseases of foliage plants

Material Information

Common fungal root rot diseases of foliage plants
Series Title:
ARC-A research report
Chase, A. R ( Ann Renee )
Agricultural Research Center (Apopka, Fla.)
Place of Publication:
Apopka Fla
IFAS, University of Florida, Agricultural Research Center-Apopka
Publication Date:
Physical Description:
5 p. : ; 28 cm.


Subjects / Keywords:
Foliage plants -- Diseases and pests -- Florida ( lcsh )
Fungal diseases of plants -- Florida ( lcsh )
Plant roots ( jstor )
Diseases ( jstor )
Pythium ( jstor )
government publication (state, provincial, terriorial, dependent) ( marcgt )
bibliography ( marcgt )
non-fiction ( marcgt )


Includes bibliographical references (p. 5).
General Note:
Caption title.
Statement of Responsibility:
A.R. Chase.

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University of Florida
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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
70921195 ( OCLC )


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A. R. Chase1
IFAS, University of Florida LiRA
Agricultural Research Center-Apopka
ARC-A Research Report RH-81-7

The previous article in this series dealt with soilbo fefungcal-orgaiiis "

which attack stems of foliage plants. This article discusses root rots caused

by some of the same as well as closely related organisms. Control of root rot

diseases is based upon the same cultural methods as control of stem rot

diseases since many times the pathogens inhabit the soil or potting medium.

Nearly all foliage plants are subject to root rot diseases caused by

several fungi. The most common pathogens are Rhizoctonia spp., Pythium spp.,

Phytophthora spp., and Fusarium spp. These four genera account for the most

severe losses due to root rot experienced by the nurseryman. Another organ-

ism, Cylindrocladium floridanum, causes a root rot disease which has become

a serious disease of Spathiphyllum 'Clevelandii'. General symptoms of each

root rot will be discussed below but it should be kept in mind that under

many production systems more than one of the pathogens may be present and

involved in the root rot complex.

Fungi causing root rot disease occur throughout the nursery. Initially

they are found in seed beds and stock areas where they are readily identified

and diseased plants can be removed. Plant loss at any stage is very expensive

and avoidance of even low levels of pathogenic organisms is advisable. Use

of sterile or new soil as well as new pots and pathogen-free plant material

are a few of the most important methods recommended for root rot control.

Consult "Foliage Digest" [2(3):16 and 3(10):13] for additional discussion of

soilborne disease control.

Assistant Professor of Plant Pathology, Agricultural Research Center, Rt. 3,
Box 580, Apopka, FL 32703.

Root rot diseases are most severe when plants are overwatered or kept

in poorly drained, water-logged potting medium. Overwatering causes root

death due to oxygen starvation and even weakly pathogenic organisms can

invade dead roots. Once the organisms have entered the root, they advance

easily into living tissue and cause additional root loss. Always avoid use

of poorly aerated soil and overwatering.


Cylindrocladium petiole and root rot of Spathiphyllum spp. has become

a serious problem over the past three years. Identification of the cause

of root rot on this plant is especially important since symptoms of Pythium

root rot and Cylindrocladium root rot are similar. Cylindrocladium root

rot appears to be most severe in the late summer months and can escape notice

until plants collapse. Examination of the root system often reveals a com-

pletely rotten root system. Complete wilt and collapse of infected plants

are common. Some of the initial symptoms of this disease are small elliptical

lesions (spots) on the petioles and leaves of plants. Although lower leaves

sometimes turn yellow, it is not as common as with Pythium root rot. Knowing

which organism is causing root rot allows accurate chemical treatment and

the possibility of both organisms infecting plants should not be overlooked.

Control of this disease should be based first on using pathogen-free seedlings

or tissue cultured plants. Growing plants off the ground and using sterile

potting media are also very important. The disease appears to spread from

infected plants to healthy plants and all infected plants should be removed

from the growing area and destroyed as soon as they are discovered. At this

time, Spathiphyllum sp. is the only known host of Cylindrocladium sp.


Fusarium spp. does not usually cause as serious a loss in roots as other

organisms. Root rot problems diagnosed and treated for Pythium sp. alone may

not diminish because Fusarium sp. invades the root system and, in the absence

of competition from Pythium sp. develops extensively. Many plants are sus-

ceptible to Fusarium root rot including those listed for Rhizoctonia spp. and

cultural controls for Fusarium root rot are the same as for the other root


PHYTOPHTHORA and PYTHIUM (1,2,4,6,7,10)

Phytophthora and Pythium spp. are common root rot organisms of many

foliage plants. Losses are most severe in Florida in the summer when con-

ditions are wet and hot, but disease occurs throughout the year. Pythium

root rot initially is characterized by rot of the small feeder roots. The

outer portion (cortex) of the roots is easily removed from the root core.

Both Pythium and Phytophthora spp. are most severe when soils are poorly

aerated. Most diseases caused by Phytophthora spp. involve both stems and

roots of plants which were discussed in the.previous article. Diseases

caused by Pythium spp. generally damage the root area most extensively.

Since roots do not absorb as much water when they are infected with root rot

organisms, tops of infected plants often wilt. Always examine roots of a

wilted plant to check for signs of root rot prior to watering the plants.

The addition of water to Pythium or Phytophthora spp. infected plants in-

creases the activity of these fungi. In addition to wilting, infected

plants show symptoms on their lower leaves of chlorosis or yellowing. Many

growers use this symptom as a positive diagnosis of Pythium root rot, but

since other factors may cause yellow lower leaves this should not be the

only criterion. Always examine the roots being sure to look for the death

and rot of feeder roots. The chemicals which control Pythium spp. do not

always give good control of Phytophthora spp. and unless a broad spectrum

treatment is used the organism causing the root rot should be identified

through isolation and culturing.


Rhizoctonia sp. is one of the most important root rot organisms of

seedlings and small plants. This organism causes damping-off of seedlings

and seed rot. There are many plants susceptible to Rhizoctonia root rot

including ferns, marantas, palms, philodendrons, pileas, pothos and syngon-

iums. Controlling an initial infection is important since it is easily

spread due to its wide host range. Although Rhizoctonia may be active

throughout the year, it is most severe during the summer when warm, wet

conditions prevail. Rhizoctonia sp. usually attacks plants at the soil

line and causes root loss and constriction of the stem which results in

girdling and death of the tops. As mentioned in the first article of this

series, this organism can attack leaves as well as roots and is especially

severe if plants are grown closely together and kept moist. Entire stock

beds are lost to Rhizoctonia infections in very short periods of time.

Since this organism develops rapidly, it must be diagnosed promptly and

controlled to minimize losses. By far, the best method of control is

avoidance of the disease through use of sterile potting media and potsand

growing plants away from native soil.

Since nearly all foliage plants are subject to the root rots listed above,

there was no table of hosts included in this article. Prevention is the key

to control of root rots and should be standard practice on all the plants you




1. Alfieri Jr., S. A. and J. W. Miller. 1971. Basal stem and root rot
of Christmas cactus caused by Phytophthora parasitica. Phytopath.
2. Averre III, C. W. and J. E. Reynolds. 1964. Phytophthora root and
stem rot of Aloe. Proc. Fla. State Hort. Soc. 77:438-440.
3. Knauss, J. F. 1973. Rhizoctonia blight of syngonium. Proc. Fla.
State Hort. Soc. 86:421-424.
4. Knauss, J. F. 1975. Control of basal stem and root rot of Christmas
cactus caused by Pythium aphanidermatum and Phytophthora parasitica.
Proc. Fla. State Hort. Soc. 88:567-571.
5. Millikan, D. F. and J. E. Smith, Jr. 1955. Root rot of pothos, a
disease caused by Rhizoctonia. P1. Dis. Reptr. 39:240-241.
6. Munnecke, D. E. and Philip A. Chandler. 1953. Some diseases of
variegated Peperomia. P1. Dis. Reptr. 37(8):434-435.
7. Raabe, Robert D., J. H. Hurlimann and B. Bruckner. 1975. A root and
stem rot complex of Christmas cactus and its control. Calif. P1. Path.
8. Schoulties, C. L. and N. E. El-Gholl. 1980. Root and petiole rot of
Spathiphyllum sp. 'Clevelandii' caused by Cylindrocladium floridanum.
P1. Path. Circ., Fla. Dept. Agric. & Cons. Serv., Div. of P1. Ind.,
Circ. No. 218.
9. Schoulties, C. L. and N. E. El-Gholl. 1980. Pathogenicity of Cylin-
drocladium floridanum on Spathiphyllum sp. cv. Clevelandii. Proc.
Fla. State Hort. Soc. 93:183-186.
10. Schulman, J. F. 1971. Etiology of a disease complex in Chamaedorea
elegans. Univ. of Fla., MA Thesis, 27 pp.

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