Fungi for Biological Control of Weedy Cyperaceae, With Emphasis on Purple and Yellow Nutsedges ( Cyperus rotundus and C. esculentus )

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Purple and yellow nutsedges (Cyperus rotundus and C.
esculentus) are widely distributed weeds in many tropical
and subtropical regions of the world. Nutsedge management
is difficult partly because of their ability to produce
numerous tubers that sprout readily and produce more tuber
a few weeks after sprouting, thus perpetuating the weed.
These weeds are generally considered among the worst
weeds (Doll, 2000; Holm et al., 1991), particularly in
vegetable crops, for which the availability of selective
chemical herbicides is very limited or completely lacking.
Purple nutsedge is more commonly found in irrigated, warm
regions, whereas yellow nutsedge is predominant in wet
and/or cool environments. However, both species may
coexist in subtropical regions such as northern Mexico and
the southern USA.
The effects of purple nutsedge interference with vegetable
crops can be devastating. When competing season-long with
eggplant (Solanum melongena), bell pepper (Capsicum
annuum) and tomato (Lycopersicon esculentum), purple
nutsedge reduced crop yield by 28, 65, and 70%, respec-
tively (Morales-Payan et al., 1997; Morales-Payan & Stall
2001, 2003, and 2004). William and Warren (1975)
reported that purple nutsedge reduced cabbage (Brassica
oleracea var. capitata) and onion (Allium cepa) yield by 35
and 89%, respectively. Yellow nutsedge interference may
also reduce crop yields drastically. Yellow nutsedge interfer-
ence reduced the yield of asparagus (Asparagus officinalis)
(Agamalian, 1996) by 16%, eggplant by 20% (Morales-
Payan & Stall, 2004), onion by 45% (Keeling et al., 1990),
tomato by 65% (Morales-Payan et al., 2003c), and bell
pepper by 89% (Motis et al., 2001). In direct-seeded and
transplanted watermelon (Citrullus lanatus), season-long
interference from yellow nutsedge resulted in almost
complete yield loss (Buker et al., 2003).
In developing countries and in organic systems, nutsedges
are commonly managed by labor-intensive means such as
mulching, hoeing and cultivation, which may be expensive and
time consuming, may be insufficient to suppress nutsedge
and/or may need to be repeated during the season. In most
instances, shoot removal by mechanical and/or chemical
means may retard nutsedge growth and tuber production, but
repeated treatments are usually needed to suppress the weed to
a sufficient extent or to reduce its competitive ability with
crops (De la Cruz & Merayo, 1990; Keeling, 1990).
Efficacious chemical herbicides for nutsedge control may be
available for few crops (such as halosulfuron [3-chloro-5-
(4,6-dimethoxypyrimidin-2-ylcarbamoylsulfamoyl)-1-
methylpyrazole-4-carboxylic acid] for tomato), and/or
systems based on polyethylene mulching and methyl
bromide soil fumigation have been used as (so far) the only
FUNGI FOR BIOLOGICAL CONTROL OF WEEDY CYPERACEAE,
WITH EMPHASIS ON PURPLE AND YELLOW NUTSEDGES
(CYPERUS ROTUNDUS AND C. ESCULENTUS)
J. Pablo Morales-Payan,
1,2
Raghavan Charudattan,
1
and William M. Stall
2
review the opportunities for the
control of nutsedges using mycoherbicides
1
Department of Plant Pathology and
2
Horticultural Sciences Department University of Florida, PO Box 110690, Gainesville, FL, USA.
BIOLOGICAL CONTROL OF CYPERUS SPECIES
Keywords
biocontrol, bioherbicide, biological control, Cyperaceae, integrated
weed management, mycoherbicide, nutsedge, organic agriculture,
weeds.
Nutsedge
Nutsedge in tomatoes
148 Outlooks on Pest Management – August 2005 DOI: 10.1564/16aug02
© 2005. Research Information Ltd. All rights reserved

practical and successful means for sufficient nutsedge
suppression (Chellemi, 2001). Environmental concerns
prompted the phase out of methyl bromide as an agricultural
soil fumigant in developed countries as of January 1, 2005.
Thus, the importance of nutsedges as problematic weeds is
likely to increase regardless of production system (conven-
tional or organic) in most horticultural crops infested with
those weeds. Efficacious bioherbicides for nutsedges may be a
valuable addition to current management strategies in conven-
tional production systems lacking chemical means for
nutsedge suppression, as well as in organic production
systems in which chemical herbicides are not permitted.
Biological enemies of nutsedge in nature
Many organisms have been documented as causing disease
or feeding on nutsedges in nature. Phatak et al. (1987)
published a partial list of previously reported natural
enemies of purple and yellow nutsedges, which contained
132 species of insects, 26 species of fungi, 10 species of
nematodes, 2 species of bacteria and one virus. Their list
also included farm animals such as geese (genera Anser,
Branta, and Chen), ducks (Anas spp.), and pigs (Suis spp.).
A number of organisms have been proposed as potential
agents for nutsedge control, such as Aleurocybotus sp.,
Antonina australis, Athesapeuta cyperi, Bactra minima
minima, B. verutana, B. truculenta, B. venosana, Chorizo-
coccus rostellum, Dercadothrips caespitis, Phenacoccus
solani, Rhizoecusi cacticans, Schoenabius sp., Sphenophorus
phoeniciensis (Mercado, 1979), and Puccinia canaliculata
(Phatak et al., 1987). Unfortunately, in most cases the results
of their evaluations were insufficient (partially due to a lack of
sustained research efforts), or nutsedges were never suffi-
ciently controlled to justify their commercial utilization. For
example, there has been extensive research on the use of the
moth Bactra verutana, which feeds on the shoots of nutsedge.
In numerous greenhouse and field experiments under different
environmental conditions, Bactra larvae were able to partially
destroy nutsedge shoots by feeding on them, but new shoots
sprouted from the tubers shortly afterwards, and the nutsedge
was able to produce new tubers (Frick, 1982; Frick &
Chandler, 1978; Frick & Wilson, 1981; Frick et al., 1978;
Frick et al., 1983; Porter, 1995). Similarly, in controlled
conditions, Bactra minima and B. venosana did not signifi-
cantly reduced nutsedge density (Phatak et al., 1987). In Italy,
B. furfurana, B. lancealana, B. robustana, B, venosana, and
B. bactrana were successful in partially defoliating purple
nutsedge, but tubers were undamaged and nutsedge recovered
(Trematerra & Ciampolini, 1989). Other insects feeding on
nutsedge were also pests of important crops or were crop
disease vectors (Charudattan & DeLoach, 1988) and/or were
cannibalistic and inflicted too little damage on nutsedges
(Story & Robinson, 1979), which disqualified them as useful
weed biocontrol agents.
Fungi associated with nutsedges and their
potential for biocontrol
Amongst nutsedge pathogens, fungi are the most abundant
(over 70 species) and the most studied as potential biological
herbicides. The list of fungi genera associated with purple
and/or yellow nutsedge includes Alternaria, Ascochyta,
Balansia, Cercospora, Chaetophoma, Cintractia, Claviceps,
Cochliobulus, Corynespora, Curvularia, Dactylaria,
Dreshclera, Duosporium, Entyloma, Fusarium,
Macrophomina, Marasmius, Phaeotrichoconis, Pythium,
Phyllosticta, Phytophthora, Puccinia, Rhizopus, Sclerotinia,
Septoria, Tanatephorus, and Uredo. For some of these fungi,
there is documented research on their evaluation as potential
bioherbicides. For other fungi, only their occurrence as
nutsedge pathogens has been reported (Mello et al., 2003a;
Betria, 1973; Clay, 1986; Barreto & Evans, 1995, Evans,
1987; Kadir et al., 2000a; Prakash et al., 1996; Pomella &
Barreto, 1999; Upadhyay et. al., 1991; Welles, 1922). The
following summarizes the documented highlights,
advantages, and disadvantages of fungi in several genera to
be developed as bioherbicides.
Balansia
Inflorescence malformation and smut caused by Balansia
cyperi have been reported in purple nutsedge and green
flatsedge (C. virens) in the USA (Clay, 1986), in purple
nutsedge in the Dominican Republic (Morales-Payan et al.,
1998), and in purple nutsedge and royal flatsedge (Cyperus
elegans) in Mexico (Carrión & Chacón, 1993). Stovall and
Clay (1988) found that purple nutsedge plants inoculated
with B. cyperi produced fewer flowers and shoot biomass
than non-inoculated plants. However, inoculated plants also
produced more tubers (although smaller) than disease-free
plants. Moreover, nutsedge plants infected by B. cyperi were
less susceptible to Fusarium oxysporum, Rhizoctonia solani
and R. oryzae, and such fungal antagonism would be coun-
terproductive for weed suppression. Furthermore, fall
armyworms (Spodoptera frugiperda), which feed on
nutsedge, seemed to favor nutsedge plants not infected with
B. cyperi, as compared to nutsedge plants infected by this
fungus. Since infected nutsedge plants actually increase their
reproductive potential (more tubers) and repel other natural
enemies, there would seem to be little benefit from using B.
cyperi for purple nutsedge management.
Curvularia
De Luna et al. (1998, 2002a) reported the occurrence of
Curvularia tuberculata and C. oryzae on rice sedge
(Cyperus difformis), rice flatsedge (C. iria), and globe
fringerush (Fimbristylis miliacea) in the Philippines. When
provided with long dew period (24 hours) and high
temperature (28 C) conditions, inoculation on those three
weedy Cyperaceae resulted in rapid leaf blighting, followed
by seedling death within two weeks of inoculation. The two
fungal species were also pathogenic to purple nutsedge, but
did not cause plant death. Some rice cultivars were found to
be susceptible to some C. tuberculata isolates, but other rice
cultivars were tolerant to all the isolates tested (De Luna et
al., 2002b).
Shelby and Bewick (1991) conducted field experiments
spraying spores of Curvularia lunata for purple nutsedge
suppression in tomato. The pathogen produced typical
disease symptoms on nutsedge, but the extent of control was
not satisfactory. Moreover, C. lunata is known to cause a
Outlooks on Pest Management – August 2005 149
BIOLOGICAL CONTROL OF CYPERUS SPECIES

stem disease in cassava (Manihot esculenta) (Msikita et al.,
1997), rice (Chu & Chen, 1973), and bentgrass (Agrostis
sp.) (Muchovej & Couch, 1987), which may be cause of
concern when the fungus is intended for use in those crops.
Whether the C. lunata isolate of Shelby and Bewick will
infect these crops has not been determined (the isolate could
have high specificity).
Based on the limited information available, potential
issues of host specificity and low efficacy may limit practical
applications for C. lunata. Because the humid environment
in which rice is commonly grown is bound to favor disease
progress, one of the main restraints for bioherbicide efficacy
(dew period, relative humidity) should not limit Curvularia
tuberculata as a biocontrol agent in rice. The susceptibility
of some rice cultivars may be an important issue, particu-
larly if the fungus is applied in areas where several rice
cultivars are grown in adjacent farms or fields.
Ascochyta
In India, Upadhyay et al. (1991) reported a purple nutsedge
leaf blight caused by Ascochyta cypericola. This fungus is
pathogenic only to plant species within the genus Cyperus,
and disease severity in purple nutsedge was reported to be
extensive. In addition, Stierle et al. (1991) reported that A.
cypericola produced cyperine, a phytotoxin that may have
potential as a natural herbicide (Dayan & Allen, 2000). A
related species, Ascochyta cyperiphthora sp. nov., was found
to cause leaf scorching in purple nutsedge in Brazil (Pomella
& Barreto, 1997), but its efficacy for biocontrol has not
been documented.
Information on Ascochyta spp. and/or its phytotoxin(s)
for Cyperaceae biocontrol is scarce, but what has been
reported may warrant further research. If efficacious,
selective, and economical, phytotoxins may prove more
practical than the fungi themselves, since the dew period,
relative humidity, and temperature requirements of the fungi
would be bypassed.
Puccinia
Several species in the genus Puccinia have been reported
attacking nutsedges, (predominantly yellow nutsedge) in the
USA (Phatak, 1984), Brazil (Barreto & Evans, 1995),
Panama (De la Cruz & Merayo, 1990; Esquivel, 1991),
India (Bedi & Sokhi, 1994), and Dominican Republic
(Morales-Payan et al., 1998). The species P. canaliculata and
P. romagnoliana seem to be most widespread. Researchers
such as Barreto and Evans (1995) have questioned the
taxonomic validity of several Puccinia species reported in
the literature. Barreto and Evans (1995) studied a complex
of six Puccinia rust fungi infecting purple nutsedge in Brazil.
From their taxonomic research, those authors concluded
that Puccinia conclusa, P. cypericola and P. philippensis
should be considered synonyms of P. canaliculata.
Okoli et al. (1997), using random amplified polymorphic
DNA analysis, found that previously observed differential
susceptibility of yellow nutsedge biotypes to P. canaliculata
were due to extensive genetic variability between yellow
nutsedge populations from different locations in the USA
and other countries. In contrast, there was less genetic
variability between purple nutsedge biotypes, which would
make them more likely to respond to similar extents to
applications of P. canaliculata. Unfortunately, most purple
nutsedge biotypes exhibit a low level of susceptibility as
compared to yellow nutsedge.
Scheepens and Hoogerbrugge (1991) tested a P. canalicu-
lata strain from the USA on various Cyperaceae in the
Netherlands. Cyperus fuscus was infected by the fungus and
developed small pustules. C. esculentus leptostachyus from
several locations in the Netherlands were found to be differ-
entially susceptible to the fungus, from resistant to high
susceptibility (as interpreted from pustule number and size).
A C. esculentus selection grown as a crop and weedy C.
esculentus biotypes were resistant to the fungus. Other
Cyperaceae tested (Cyperus albostriatus, C. alternifolius, C.
flavescens, C. rotundus, Carex hirta, Eleocharis palustris,
and Scirpus maritimus) were also resistant to P. canaliculata.
When P. canaliculata spores were sprayed on yellow
nutsedge in Georgia (USA), tuber productivity was signifi-
cantly reduced, 90% of the shoots were killed within five
weeks of application, and the production of new shoots was
reduced by 66% as compared to control plants. When P.
canaliculata spores were applied with the chemical herbicide
paraquat [1,1’-dimethyl-4-4’-bypyridinium ion], yellow
nutsedge shoot production was 99% lower than in control
plants; in contrast, in plants sprayed with paraquat only,
shoot production was reduced by 10% as compared to
control plants (Phatak, 1984; Phatak et al., 1983, 1984, and
1987). Bruckart et al. (1988) combined P. canaliculata with
bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one
2,2-dioxide] (0.3 or 0.6 kg a.i./ha), resulting in reduced
disease (50%) as compared to P. canaliculata without
bentazon. P. canaliculata reduced the number of tubers
(44%), but not the number of shoots produced per yellow
nutsedge plant. In yellow nutsedge infested-soybean
(Glycine max), P. canaliculata combined with the chemical
herbicides betanzon, acifluorfen [5-(2-chloro-a,a,a-trifluoro-
p-tolyloxy)-2-nitrobenzoic acid], or imazaquin [(RS)-2-(4-
isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)quinoline-3-
carboxylic acid], resulted in better yellow nutsedge control
than the rust or the chemical herbicides alone (Callaway et
al., 1986). Beste et al. (1992) applied P. canaliculata mixed
with the chemical herbicide pebulate [S-propyl
butyl(ethyl)thiocarbamate] for yellow nutsedge suppression
in tomato, and found the same extent of control with the
mixture as with pebulate alone.
Major efforts have been made to develop P. canaliculata
into a commercial bioherbicide (Phatak, 1992) and the Envi-
ronmental Protection Agency of the USA has granted P.
canaliculata a bioherbicide registration with the name of
‘Dr. BioSedge’. However, difficulties in large-scale
production of P. canaliculata spores (an obligate parasite),
its low efficacy against certain yellow nutsedge biotypes, and
its low or no pathogenicity against purple nutsedge, have
prevented wide acceptance of this fungus as a commercial
bioherbicide.
In India, Puccinia romagnoliana was found causing a rust
disease on purple nutsedge. In field trials in which this
potential bioherbicide was applied on purple nutsedge, the
rust reduced plant fresh and dry weights by 64% and 56%,
respectively, and tuber number and weight were reduced by
150 Outlooks on Pest Management – August 2005
BIOLOGICAL CONTROL OF CYPERUS SPECIES

34% and 83%, respectively. Nutsedge plants between 2 and
4 weeks after emergence were the most affected in terms of
growth reduction after being treated with P. romagnoliana
(Bedi & Sokhi, 1994; Bedi et al., 1995). In Israel, results by
Dinoor et al. (1994a, 1994b) support the findings of Bedi et
al. (1995). In India, Gupta (2002) showed that this potential
bioherbicide did not cause disease in mulberry (Morus alba),
but significantly reduced purple nutsedge shoot growth and
tuber production. From the practical point of view, the
major obstacles for working with Puccinia rusts seem to be
the need to maintain large amounts of infected plants for
mass-production of inoculum, and the variability of results
when sprayed on different biotypes.
Cercospora
Species in the genus Cercospora have been reported affecting
nutsedges in several countries of the Americas. Gamboa and
Vandermeer (1989) found an unidentified Cercospora
species infecting purple nutsedge in Nicaragua. In that
instance, disease severity was greater in purple nutsedge
growing in maize and bean crops as compared to nutsedge
growing alone, which may be partially explained by
increased relative humidity by the crop canopies.
Cercospora caricis was reported to cause a foliar disease
in yellow nutsedge in North Carolina (USA) (Blaney & Van
Dyke, 1988) and in purple nutsedge in southern Brazil
(Barreto & Evans, 1995; Ribeiro et al., 1997). Inglis et al.
(2001) used molecular markers to determine the genetic
relationship between isolates from Brazil and one isolate
from the USA, and found that Brazilian isolates were closely
related among them, but were distantly related to the isolate
from the USA. The genetic differences between strains a
pathogen may have important implications on C. caricis
virulence towards host weeds. Aly et al. (2001) was able to
genetically transform C. caricis using a biolistic system, and
suggested that their approach could be used to enhance the
pathogenicity of C. caricis and its efficacy for purple
nutsedge control. The potential for enhancing bioherbicide
efficacy through molecular transformation has also been
debated for other biocontrol agents as well (Kistler, 1991;
Templeton & Heiny, 1989; Gressel, 2003). However,
organic growers and consumers that oppose the use of
genetically modified organisms would object to biocontrol
agents enhanced by molecular transformation. Registration
of a genetically engineered pathogen, which may attack non-
target plants, will be a difficult issue for regulatory agencies
to resolve.
There has been extensive research on C. caricis inoculum
production, application, and efficacy in Brazil. C caricis is
known to have slow and sparse sporulation in most culture
media (Barreto & Evans, 1995). However, Ribeiro (1997)
and Borges Neto (1997) developed model systems for mass
production C. caricis inoculum, which improves the
likelihood of its developing into a commercial bioherbicide.
In greenhouse experiments, Borges-Neto et al. (1998a,
1998b, 2000) studied the host/pathogen relationship and the
effect of C. caricis on purple nutsedge as affected by weed
age, inoculum (mycelium) application rate, and dew period
after application. C. caricis was found to penetrate purple
nutsedge leaves only through open stomata (Burgos Neto et
al., 1998a). Plants 3- to 4-weeks old were more susceptible
to this potential bioherbicide that younger or older plants,
and the best results were obtained with 20 g of fresh
mycelium per liter followed by a dew period of 48–72 hours
(Burgos Neto et al., 2000). Increasing the number of appli-
cations resulted in increased disease severity: the leaf area
affected by one, two, and three applications was approxi-
mately 63, 73, and 84%, respectively (Borges Neto et al.,
2000). In field trials, C. caricis reduced purple nutsedge
shoot and tuber dry weight (Borges Neto, 1997), and three
applications were as affective as 2,4-D and hoeing in
suppressing purple nutsedge (Teixeira, 1999).
Borges Neto et al. (1998b) tested various surfactants to
improve C. caricis efficacy to suppress purple nutsedge. In
the greenhouse, the best results were found with a
hydrophilic mucilage of Plantago psyllium, polyoxyethylene
monolaureate, sucrose, an emulsifying synthetic resin + an
anionic tensoactive agent, and polyoxyethylenalquil phenol
ether. In those experiments, the blight caused by C. caricis
covered approximately 84% of the leaf area and killed 40%
of the leaves in purple nutsedge plants 3 to 4 weeks old.
Compatibility with pesticides may help C. caricis fit in
integrated management strategies. The effects of several
pesticides on the growth of the fungus were evaluated by
Mello et al. (2003b), who found normal C. caricis growth in
culture medium which was amended with copper
oxychloride (up to 1000 parts per million), glyphosate [N-
(phosphonomethyl)glycine], oxyfluorfen [2-chloro-a,a,a-
trifluoro-p-tolyl 3-ethoxy-4-nitrophenyl ether] and
chlorimuron-ethyl [ethyl 2-(4-chloro-6-methoxypyrimidin-
2-ylcarbamoylsulfamoyl)benzoate].
Blaney and Van Dyke (1988) reported the production of
the phytotoxin cercosporin from C. caricis. Cercosporin is
known to be a host non-selective toxin able to absorb and
transfer light energy to oxygen, and to generate reactive
oxygen species that cause cell membrane disruption (Daub
& Hangarter, 1983; Daub & Ehrenshaft, 2000).
C. caricis has been studied extensively and there is ample
information on its biology, epidemiology, effect of
surfactants, and efficacy on purple nutsedge under green-
house and field conditions. There are viable inoculum
production models, and its compatibility with several
chemical pesticides is known. Little is documented, however,
on the impact of C. caricis applications on the yield of
nutsedge-infested crops. If yield loss in nutsedge-infested
crops can be reduced to satisfactory levels by application of
C. caricis, this fungus may be a likely candidate to become a
commercial bioherbicide for purple nutsedge management.
Dactylaria
Lutrell (1954) found the fungus Dactylaria higginsii in
Georgia, USA (at the time, it was reported as Pyricularia
(Piricularia) higginsii). Kadir and Charudattan (1996)
reported the occurrence of D. higginsii in Florida. The fungus
has also been reported in Brazil (Barreto & Evans, 1995),
Panama (De la Cruz & Merayo, 1990; Esquivel, 1991), and
the Dominican Republic (Morales-Payan et al., 1998).
Typical symptoms (dark brown oval-shaped leaf spots,
eventually coalescing and causing a leaf blight) are
noticeable 4 to 15 days after spraying the fungus on the
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BIOLOGICAL CONTROL OF CYPERUS SPECIES

weed canopy. In greenhouse experiments conducted in
Florida, a D. higginsii isolate from Gainesville (Florida)
caused severe symptoms in purple and yellow nutsedges,
annual sedge (C. compressus), globe sedge (C. globosus),
rice flatsedge (C. iria), and green kyllinga (Kyllinga
brevifolia). The authors concluded that D. higginsii was a
promising biological agent to suppress at least five species of
Cyperus, including purple and yellow nutsedges (Kadir &
Charudattan, 1996).
In purple nutsedge, increasing the number of applications
and the spore concentration resulted in increased weed
suppression. When D. higginsii was applied three times at a
concentration of 10
6
conidia per ml, purple nutsedge shoot
and tuber growth were reduced by approximately 70%, and
approximately 90% of the plants died (Kadir et al., 2000b).
In tomato competing with purple nutsedge under
greenhouse conditions, D. higginsii applications significantly
reduced the interference effect of purple nutsedge with the
crop (Kadir et al., 1999). The application of the fungus also
suppressed purple nutsedge growth in the field (Kadir et al.,
2000b).
Environmental conditions influence the efficacy of D.
higginsii for nutsedge suppression. Under field and
greenhouse conditions, temperature, dew period, and
relative humidity during periods of inoculation and disease
progress proved to be important for disease progress. In the
greenhouse, Kadir et al. (2000a) found that a minimum dew
period of 12 h at a 25 C temperature was necessary for D.
higginsii to kill almost 100% of a population of young
purple nutsedges, and that the dew period may be partially
substituted by using selected humectants in the spray
mixture. In the field, high relative humidity and tempera-
tures between 25 and 30 C appear to favor the activity of
the fungus. In untreated fields in humid regions of the
Dominican Republic, purple nutsedge plants with
Dactylaria leaf spots were found, whereas in dry regions of
the country diseased purple nutsedge plants were rare
(Morales-Payan et al., 1998). In field experiments during the
dry season (<40% relative humidity) in Florida, Puerto
Rico, and the Dominican Republic, the progress of disease
caused by spraying D. higginsii was limited, resulting in low
or non-significant yield loss reduction in the nutsedge-
infested crops (Semidey et al., 2003; unpublished data by the
authors). In contrast, during humid seasons, D. higginsii has
proven more effective in suppressing purple nutsedge. In
field experiments in Florida, D. higginsii was applied post-
emergence (1 × 10
6
conidia per ml) on purple nutsedge-
infested bell pepper during the humid season; typical
symptoms of Dactylaria blight developed within 10 days of
applying the fungus. When the fungus was sprayed one
week after weed emergence, the yield of extra-large
(“Fancy”) fruit improved significantly as compared to
weedy plots where the fungus was not sprayed. Repeated
applications within 30 days after transplanting the crop
further decreased yield loss (as compared to untreated
nutsedge-infested pepper). However, in all the bioherbicide
treatments pepper yield losses were significant as compared
to the weed-free crop (Morales-Payan et al., 2003a).
Surfactants play an important role in D. higginssi efficacy
for purple nutsedge control. In field and greenhouse
experiments, the best results were usually found when
spraying the potential bioherbicide with vegetable oils, as
opposed to other surfactants (Morales-Payan et al., 2003b).
Rosskopf et al. (2003) applied D. higginsii on purple
nutsedge-infested plots during the humid fallow season
(summer) in Florida, and found that nutsedge suppression
was comparable to that found in plots managed with
glyphosate and disking. Thus, D. higginsii may be used for
nutsedge population reduction prior to the autumn crop
season as an alternative for glyphosate in organic and
conventional cropping systems.
A commonly raised question is how well would a
potential bioherbicide fit with other crop production and
protection practices. The percentage of D. higginsii spore
germination was reduced when exposed to thiophanate
[dimethyl 4,4’-(o-phenylene)bis(3-thioallophanate)], oxy-
fluorfen, glyphosate, sethoxydim [(±)-(EZ)-2-(1-ethoxyimi-
nobutyl)-5-[2-(ethylthio)propyl]-3-hydroxycyclohex-2-
enone], fosetyl-Al [aluminium tris-O-ethylphosphonate] and
dicofol [2,2,2-trichloro-1,1-bis(4-chlorophenyl)ethanol], but
spore germination percentage was equal or higher than
control spores (treated with water) when exposed to
cyromazine [N-cyclopropyl-1,3,5-triazine-2,4,6-triamine],
diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], imazapyr
152 Outlooks on Pest Management – August 2005
BIOLOGICAL CONTROL OF CYPERUS SPECIES
Dactylaria symptoms

[2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)nicotinic
acid], mefenoxam [methyl N-(methoxyacetyl)-N-(2,6-xylyl)-
D-alaninate] and copper hydroxide (Yandoc et al., 2003).
Thus, D. higginsii would be compatible with some agri-
chemicals, but not with others.
Several cultural media have been evaluated for mass
production of D. higginsii (Wyss et al., 1999), and the
spores can be stored dry for several years retaining
infectivity. Thus, mass production and storage should not be
major hurdles for commercial D. higginsii production.
Research has shown that some surfactants can partially
substitute for the dew period requirements, that the fungus
is compatible with some chemical pesticides, and that yield
loss can be significantly reduced in a number of purple
nutsedge-infested crops. To be used as the main means of
nutsedge suppression in a production system, the D.
higginsii technology would need to be refined further, as the
yield loss found in nutsedge-infested crops has usually been
higher than 10%, which may be unacceptable for growers.
Improvements on efficacy (and thus lower yield losses) may
be attainable with the use of more effective surfactants
and/or selecting more virulent isolates of the fungus. Never-
theless, the current D. higginsii technology may be an
important component in an integrated nutsedge management
strategy.
Summation
It is unlikely that any single bioherbicide documented to
date will provide a “silver bullet” control of nutsedges.
However, documented research results show that several
fungal species have the potential to be developed into
bioherbicides that may play an important role in integrated
nutsedge management strategies in conventional and organic
production systems.
If bioherbicides are to be used as the only means of
nutsedge management, the major constraints for their
practical utilization are the need for humid conditions and
prolonged dew period after application (partially solved
with the use of selected surfactants), the need of several
applications early in the crop season (due to rapid shoot
regrowth from tubers), their lack of total weed suppression
under field conditions, and yield losses higher than
acceptable levels. However, it has been long recognized that
in most horticultural crops and cropping systems, nutsedges
need to be confronted using integrated management systems
(using more than one means of suppression), in which
potential bioherbicides such as Cercospora caricis,
Dactylaria higginssi, and Puccinia spp. may be important
components.
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J. Pablo Morales-Payan is a Research Associate at the Horticultural
Sciences Department of the University of Florida at Gainesville,
Florida, USA. Current research topics include bioherbicide
development and assessment, weed ecology, integrated weed
management, yield loss assessment, and growth regulation in horti-
cultural crops. The main model weeds in his research are in the
families Cyperaceae, Amaranthaceae, Commelinaceae, Asteraceae,
and Poaceae.
Raghavan Charudattan is a Professor with the Plant Pathology
Department of the University of Florida at Gainesville, Florida, USA.
His research focuses on weed management using specific plant
pathogens.
William M. Stall is a Professor with the Horticultural Sciences
Department of the University of Florida at Gainesville, Florida, USA.
His research focuses on weed management in vegetable crops,
including the influence of chemical, biological, and cultural practices
on weed/crop interactions and crop yield.
Related articles in Outlooks on Pest Management (Pesticide Outlook) include 2004 15(1) 18;
2004 15(2) 64 and 70; 2004 15(2) 76
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