Title: Cylindrocladium black rot (cbr) of peanut, soybean, and forage legumes in Florida
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00066811/00001
 Material Information
Title: Cylindrocladium black rot (cbr) of peanut, soybean, and forage legumes in Florida
Series Title: Plant Pathology Fact Sheets PP-139
Physical Description: Book
Language: English
Creator: Kuckarek, Tom A.
Affiliation: University of Florida -- Florida Coopertive Extension Service -- Department of Plant Pathology -- Institute of Food and Agricultural Sciences
Publisher: Department of Plant Pathology, Institute of Food and Agricultural Sciences, University of Florida
Publication Date: 1995
Spatial Coverage: North America -- United States of America -- Florida
Funding: Florida Historical Agriculture and Rural Life
 Record Information
Bibliographic ID: UF00066811
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved by the source institution and holding location.

Table of Contents
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Full Text

Plant Pathology Fact Sheet

Cylindrocladium Black Rot (CBR) of Peanut,

Soybean, and Forage Legumes in Florida
Tom Kucharek, Professor and Extension Plant Pathologist, Plant Pathology
Department, University of Florida, Gainesville FL 32611. 1995; Revised, Febru-
ary, 2000.

Florida Cooperative Extension Service/ Institute of Food and Agricultural Sciences/ University of Florida/ Christine Waddill, Dean


The fungal disease Cylindrocladium black
rot (CBR) was first found in 1965 in peanut in
southwest Georgia. It was not until 1975 and
1976 that CBR was first found in peanut in
Florida, in Alachua and Columbia counties. In
the mid 1980s CBR was found in peanut in the
panhandle section of Florida. Since 1975, CBR
has been found in alfalfa, clovers, and soybean.
Also, CBR has been found in hairy indigo,
coffeeweed, and beggarweed in Florida.
Among the weed species in the central Florida
area, hairy indigo is the weed that is most com-
monly seen with CBR. In soybean, this disease
is sometimes called red crown rot. Other crops
reported to be susceptible to CBR are cowpea,
bean, blueberry, and tobacco but in Florida CBR
has not been found in these four crops. How-
ever, in blueberry, a related fungus has caused
disease in Florida.

Yield losses from CBR in some infested
fields of peanut in Florida have exceeded 50%.
Cylindrocladium black rot has become a limit-
ing factor for the production of peanut in some
fields in the panhandle area, particularly in
Santa Rosa County. In general, CBR appears to
be gradually increasing in severity in peanut
throughout the peanut-producing areas of
Florida. Additionally in Florida,
Cylindrocladium black rot has caused signifi-
cant damage to plantings of alfalfa but levels

of damage from CBR in soybean have been
minimal. However, in Louisiana severe dam-
age to soybean from CBR has been reported.

The fungus that causes CBR is
Cylindrocladium parasiticum (Cylindrocladium
crotalariae). The sexual stage, Calonectria ilicicola
(Calonectria crotalariae), produces spores called
ascospores. They are produced within bright
red spherical structures called perithecia which
sometimes can be seen on lower stems or pea-
nut pods. The asexual stage produces spores
known as conidia, which are formed externally
on infected tissue. Neither spore type is con-
sidered to be important in the causation of this
disease. However, ascospores are likely to func-
tion as sources of genetic variation within the
species. Other species of Cylindrocladium have
been reported to infect soybean.

Temperatures near 770 F are optimal for fun-
gal growth, formation of ascospores and per-
ithecia, and development of symptoms. The
severity of CBR is reduced as soil temperatures
deviate from 680 F to 860 F. Fungal growth and
production of ascospores and perithecia can
occur from 580 F to 910 F.

Ascospores can be produced more than one
time within the same perithecium. Ascospores
are discharged within a mucilaginous ooze
from the perithecium during periods of re-
duced humidity. However, ascospores lose
their germinability rapidly after discharge into


reduced humidities. Spread of ascospores is
primarily by physical contact with rain drops
or other mechanical means. High soil moisture
and abundant rainfall are favorable for infec-
tion and development of CBR.

The fungus, C. parasiticum, produces
microsclerotia. (small aggregates of hyphae
with a hardened exterior) within infected tis-
sue, particularly in roots. Microsclerotia serve
as inoculum for CBR by germinating to form
fungal strands hyphaee) in the soil. These hy-
phae penetrate root, pod (for peanut), or lower
stem tissue. Roots of peanut are commonly in-
fected via hyphae through nitrification nodules.

Microsclerotia are distributed for long dis-
tances by wind which blows crop debris and
infested soil, and by equipment and livestock
which moves soil from field to field. Additional
spread of the fungus within a field occurs with
tillage of soil and harvest operations.
Microsclerotia in soil and infected weeds dur-
ing rotation periods provide mechanisms for
long term survival of C. parasiticum. A five-year
interval of bahiagrass between peanut plantings
was inadequate to reduce CBR in one situation.

Soils that remain at 400 F or less for four
weeks or longer during the winter have fewer
sclerotia than warmer soils. Thus, winters in
Florida are not cold enough to reduce inocu-
lum (microsclerotia) for CBR. Microsclerotia
survive better when buried with tillage opera-
tions than when left on the surface of the soil
after harvest.

Some additional factors can influence the
severity of CBR. For example, nematode dam-
age can increase levels of CBR in some peanut
varieties. Damage to root systems from culti-
vation is also likely to enhance CBR.


In peanuts, symptoms generally appear dur-
ing July or August in Florida. However, in for-

age legumes, symptoms have been observed
in May to June in Florida. Cylindrocladium
black rot tends to be more severe during sea-
sons with excessive rains, particularly on
heavier (less sandy) soils. The greater severity
of CBR in Santa Rosa County and a few other
areas in the panhandle area, when compared
to the central peanut-producing area from Ocala
to Live Oak, is likely caused by the presence of
heavier soil in the panhandle area. Sandier soils
allow better drainage of excess moisture.

Like many other soilborne diseases, CBR
does not occur in a random pattern in fields.
Rather, CBR occurs in non-random patches (Fig.
1). After the disease becomes distributed within
a field across many years, the patchy occurrence
becomes less obvious. Often the more severely
affected areas in the field are in the wetter sites.
Symptoms include wilting (Figs. 1 & 2) and
eventually death of entire vines or plants (Fig.

When the fungus invades plant tissues, dis-
colored plant tissues result. Initially, infected
tissue may be brown, but usually such infected
tissue becomes black (Figs. 3 & 4). Such discol-
oration is common in lower stems, pegs, and
pods (Figs. 3 & 4). Additionally, red perithecia
can often be seen on lower stems (Fig. 3) or
pods. The presence of perithecia is useful in
distinguishing CBR from other soilborne dis-
eases, such as white mold (caused by Sclerotium
rolfsii), Rhizoctonia-induced diseases, nematode
damage, or other diseases. The soilborne dis-
ease white mold and other soilborne problems
can occur at the same time as CBR in the same
field. Occasionally in Florida, a related fungus,
Nectria spp., produces red perithecia seen on
lower stems of peanut. The importance of
Nectria spp. in relation to causation of disease
in peanut has not been determined. Another
fungus that produces reddish perithecia on
peanut is Neocosmospora sp. Its causal relation-
ship to disease in peanut is imperfectly under-
stood at this time, but it can be pathogenic.

Symptoms and signs of CBR in other legume
crops, such as soybean (Fig. 5) and alfalfa (Fig.
6), are similar to those in peanut. Infected hairy
indigo generally produces an abundance of
perithecia on the lower blackened stem. The
initial wilting associated with CBR in peanut,
soybean, alfalfa, or clovers from CBR tends to
be associated with bright yellow to red leaf dis-
coloration (Figs. 2 & 6). Browning of leaves oc-
curs later. Initial leaf discoloration associated
with white mold tends to be dull green to sil-
very. Confirmation of field diagnoses with labo-
ratory tests is recommended if any doubt ex-


At this time, tactics that are likely to elicit
total control for CBR are not available for any
susceptible crop. The best control available is
to utilize as many of the control tactics as pos-
sible for each field. If possible, avoid planting
susceptible crops in infested fields. Crop rota-
tions of peanut with four to five years of
bahiagrass have not been adequate for suppres-
sion of CBR in some situations. However, be-
cause higher levels of CBR are directly related
to higher levels of microsclerotia in soil, crop
rotation with non-susceptible crops is likely to
be useful to some degree. Susceptible weeds
such as hairy indigo, beggarweed, and
coffeeweed should be reduced or eliminated.
Such weed control should be done when the
susceptible crop is being grown and during
rotational years when the susceptible crop is
not being grown.

Plantings should be in fields that are well
drained. Soil and plant debris should be re-
moved from tractor tires and implements be-
fore moving from an infested to a non-infested
field. Later planting of peanut has resulted in
reduced levels of CBR. Because peanut is typi-
cally planted earlier than soybean in Florida,
the later planting of soybean may be why CBR
typically occurs less frequently in soybeans
when compared to peanut.

Resistance to CBR in alfalfa has been pur-
sued in Florida and elsewhere, but resistant
varieties are not currently available. Some va-
rieties of peanut (e.g., NC 10C) have low levels
of resistance to CBR for use in Virginia and
North Carolina. Comparisons of varieties in
Florida and elsewhere have resulted in less
CBR in Florunner, a commonly grown variety,
when compared to NC 10C, Florigiant, and
some other varieties. However, severe cases of
CBR in Florunner in commercial plantings in
Florida override any consideration that
Florunner possesses any useful level of resis-
tance to this disease. Some Spanish-type vari-
eties possess slight resistance to CBR. The pea-
nut varieties NC 12C, Georgia Green, Florida
MDR 98, and Southern Runner incur less dam-
age than Florunner and other susceptible vari-

Chemical control for CBR in peanut has
provided some control. In Virginia, North Caro-
lina, and to a limited extent in Georgia, preplant
fumigation with metam-sodium has been used
successfully, particularly if fumigation is
coupled with use of a resistant variety. The fu-
migant must be applied two to three weeks
prior to planting. Typically, the fumigant is
applied behind a chisel set 10 to 12" deep along
the intended center of the row followed by hill-
ing with coulters (ripping & bedding, ripping
& shipping .

In Florida, CBR has been suppressed in pea-
nut by means of post-plant sprays of select
sprayable fungicides (e.g. Folicur) at mid-sea-
son. Control from sprays has been slightly er-
ratic, but usually wilt and black pods have been
reduced and higher yields occurred. In some
situations the initial yellowing of leaves, is not
dramatically reduced but pod blemish is re-
duced dramatically. More than two tons of pea-
nut have been harvested per acre in some situ-
ations after midseason sprays were employed,
even though widespread yellowing of plants
occurred. However, if plants turn brown in the

latter stage of discoloration, i.e., turn brown af-
ter the initial yellowing, yield losses increase
drastically. Because information about chemi-
cals and varieties is likely to change, acquire
current recommendations from the University
of Florida.

Some studies show that applications of ni-
trogen reduce CBR in peanut. This tactic should
be avoided because applications of nitrogen to
peanut have reduced yields. Reduced nodula-
tion and delayed pod formation occur with in-
creases in applied nitrogen.

Figure 1. Field view of Cylindrocladium Figure 2. Wilting and yellowing of peanut
black rot in a peanut crop. with Cylindrocladium black rot.





Figure 3. Blackened lower stems of peanut
with red perithecia.

Figure 4. Symptoms of Cylindrocladium
black rot in pods and pegs of peanut.



Figure 5. Lower stem symptoms of
Cylindrocladium black rot in soybean.

Figure 6. Wilting and yellowing of alfalfa
with Cylindrocladium black rot.

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