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Copyright 2005, Board of Trustees, University
COMMON FUNGAL ROOT ROT DISEASES OF FOLIAGE PLANTS
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.