U UNIVERSITY of
2006 Florida Plant Disease Management Guide: Guava
(Psidium guajava) 1
Michael Merida and Aaron J. Palmateer2
Guava Diseases Caused by Fungi
Anthracnose is the most commonly observed
disease that affects both pre- and postharvest
management of guava. This disease can cause
considerable postharvest losses and can affect young
developing flowers and fruit. It has been reported in
all guava-growing areas around the world where high
rainfall and humidity are present.
Symptoms of this disease are observed on
mature fruits on the tree. The characteristic
symptoms consist of sunken, dark colored, necrotic
lesions. Under humid conditions, the necrotic lesions
become covered with pinkish spore masses. As the
disease progresses, the small sunken lesions coalesce
to form large necrotic patches affecting the flesh of
the fruit (Figure 1).
Figure 1. Symptoms of anthracnose on fruit.
Colletotrichum gloeosporioides (teleomorph:
Glomerella cingulata), is the pathogen responsible
for causing anthracnose. The teleomorph stage may
or may not play a role in the disease cycle.
1. This document is PP-232, one of a series of the Plant Pathology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural
Sciences, University of Florida. Original publication date June 2006. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.
2. Michael A. Merida, graduate assistant-research, Plant Pathology Department; Aaron J. Palmateer, assistant Extension scientist, Ph.D., Tropical Research
and Education Center--Homestead, FL; Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida,
The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the
products named, and references to them in this publication does not signify our approval to the exclusion of other products of suitable composition.
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University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry
2006 Florida Plant Disease Management Guide: Guava (Psidium guajava) 2
Colonies of C. gloeosporioides on
potato-dextrose agar are grayish white to dark gray.
Production of aerial mycelia by strains varies,
ranging from a thick mat to sparse tufts associated
Conidia are hyaline, unicellular, and either
cylindrical with obscure ends or ellipsoidal with a
rounded apex and a narrow, truncate base. They form
on hyaline to faintly brown conidiophores in acervuli
that are irregular in shape and approximately 500 pm
in diameter. Setae are one to four septate, brown,
slightly swollen at the base, and tapered at the apex.
Symptoms may occur on leaves, stems and fruit.
Small lesions (2-8 mm) appear as irregular to
sub-circular, dark smokey brown on the upper leaf
surface, with a darker brown, diffuse border. Under
high humidity, sporulation of the causal fungus may
be seen in lesion centers as greenish-gray, felty tufts
of mycelium. Individual lesions may coalesce to
form large areas of necrotic tissue. The fungi can
infect fruit and cause lesions and fruit cracking which
may lead to secondary infections of other
opportunistic fungi and bacteria.
Disease Cycle and Epidemiology
Conidia (asexual spores) are the fungal
structures responsible for anthracnose infection.
Conidia are produced on dead twigs, necrotic fruit
lesions, inflorescences, and leaves. Inflorescences and
young fruit are extremely susceptible and, if infected,
may cause abortion and abscission. Conidia spread
via rain splash and can cause infection; symptoms
may develop shortly thereafter on any above ground
host tissue. Latent infections are common with this
disease and may remain quiescent for months.
Control measures are needed in commercial
guava production. The use of resistant cultivars
provides the most efficient tactic in disease
management. Additional cultural control tactics used
to aide in disease management include disease
monitoring and the use of micro-irrigation. Chemical
control can be quite effective and several systemic
and non-systemic fungicides are available for use on
guava in Florida (Table 1). Timely applications
shortly before and during flowering and fruit
development are crucial for disease management;
subsequent applications may alleviate pre-harvest and
post-harvest disease on fruit.
Pseudocercospora Leaf Spot
Pseudocercospora leaf spot is prevalent in warm,
humid and rainy guava producing areas of south
The mycelium ofPseudocercosporapsidii is
internal, olivaceous, consisting of septate, branched,
smooth hyphae, 3-4 pm wide. Conidiophores are
aggregated in dense fascicles arising from the upper
cells of a light brown stroma up to 50 pm wide;
conidiophores light brown, smooth, 1 3-septate,
subcylindrical, straight to variously curved, and
unbranched. Conidia solitary, olivaceous, smooth,
non-guttulate subcylindrical to narrowly obclavate,
apex subobtuse, base narrowly obconically truncate,
straight to curved, 1 5-septate (Figure 2).
Figure 2. Conidia of Psuedocercospora psidii.
Disease Cycle and Epidemiology
The source of inoculum most likely originates
from infected leaves. The pathogens are capable of
directly penetrating host tissues. Once infected, the
2006 Florida Plant Disease Management Guide: Guava (Psidium guaiava) 3
fungus reproduces abundantly from the lower leaf class of the order Uredinales. It produces pale
surfaces. yellow, amphigenous uredinia, sub-epidermal then
becoming erumpent, in groups on brownish or
Sporulation is greatest during warm, wet weather blackish spots (up to 5 mm in diameter) (Laundon
and most abundant from May thru September. Spores and Waterson 1965). It produces urediniospores and
are disseminated via wind, splashing rain, insects and teliospores, but teliospores have not been observed in
irrigation. Florida (Leahy 2004). Urediniospores are globose,
ry s r r r r r ellipsoid to obovoid, with finely echinulate cell walls.
Very small fruit and those at or near maturity are
If observed, teliospores are ellipsoid to oblong,
less susceptible than those fruit which are one-fourth If observed, telospores are ellipsoid to oblong,
to three-fourth of full size. rounded above and narrow below, slightly constricted
at the septum, pale yellow in color and smooth.
Management Disease Cycle and Epidemiology
Due to the favorable environment for disease
t in sh Fri, s gic cmi Infection of upper and lower leaves occurs in wet
development in south Florida, strategic chemical
to moist environments within temperature ranges of
control is deemed necessary for successful guava
55 77 F (Burnett and Schubert 1985).
production. Copper based fungicides are labeled for- .
in Florida (Table 1). Urediospores germinate at temperatures in the range
the use on guava in Florida (Table 1).
of 18 220 C (64 710 F). Disease usually begins
Guava Rust to occur at the onset and development of young
shoots; leaves that are 40 days or more old have been
The rust disease can be very destructive to guava observed to be more resistant to infection (Holliday
producing regions around the world. The pathogen 1980). Urediospore dissemination occurs via
has been reported to occur in Central and South rainsplash.
America, the Caribbean and in Florida. Aside from
guava, the disease has been reported to affect other Management
members of the Myrtaceae family including allspice
Control of guava rust is based on the use of
(Pimenta dioica), Eucalyptus (Eucalyptus spp.) and
Melaleuca i(Melaluca quinquen ia) (Alfi et al. fungicides. Scouting fields for onset of disease or
Melaleuca (Melaleuca quinquenervia) (Alfieri et al.
\ +during the times of year when environmental
1994). Recently in Florida, the rust has been reported
1994). Rec y conditions are favorable for pathogen infection are
to occur in other hosts such as Myrcianthesfragrans,
recommended so that proper and timely fungicide
Myrtus communis, Callistemon viminalis, S'_-'giumll
Myru common, Callistemon inals, applications can be made. In addition, proper
jambos, S. paniculata, S. camini (Leahy 2004) and
tae, S int l H te ea 0 on cultural tactics such as proper fertilization, irrigation,
Myrtales in the family Heteropyxidaceae on the
ges Hs (Al s et 20 pruning and sanitation aide in achieving a healthy,
genus Heteropyxis (Alfenas et al. 2005).
vigorously growing tree less vulnerable to disease
The pathogen can affect foliage, young shoots, Mushroom Root Rot
inflorescences and fruit of guava. Typical symptoms
Mushroom root rot is a common and widespread
associated with this disease include distortion,
disease that affects conifers and hardwoods in
defoliation, reduced growth and if severe, mortality.
Florida. Aside from affecting Guava, the disease has
On fully expanded leaves, dark bordered, roughly
been reported on over 200 species of trees and
circular brown lesions with yellow halos develop
(Burnett and Schubert 1985).
Causal Organism Symptoms
The rust pathogen, Puccinia psidii G. Wint., is an
obligate parasite belonging to the Basidiomycete
Infected trees will usually not show any
symptoms until the disease has debilitated a
significant portion of the root system. Diseased trees
2006 Florida Plant Disease Management Guide: Guava (Psidium guaiava) 4
may exhibit a variety of symptoms, including:
thinning of the crown, yellowing of foliage,
premature defoliation, branch dieback, decaying
roots, and lesions at the root collar. On some
occasions, a tree may show symptoms of decline for
several years before dying where as in other
instances, trees may die rapidly without any visible
Mushroom root rot, caused by the fungus
Armillaria tabescens, can cause severe problems for
guava producing areas if the pathogen is present in
the field. The most notable sign of disease, if present,
is the characteristic mushrooms which develop near
the base of infected trees. The mushrooms usually
appear in fall, but they can occur at other times as
well. The mushrooms, when fresh, are tan to brown,
fleshy, with gills beneath the cap, and lacking an
annulus around the stem (Ash and Barnard 1994).
The disease may not always produce fruiting bodies
when guava trees are infected. When a tree is in
decline, and the mushrooms are absent, the fungus
can be identified by the characteristic cream -
colored mycelium just beneath the bark of infected
roots and tree bases (Ash and Barnard 1994).
Disease Cycle and Epidemiology
The fungus usually spreads vegatatively via
threadlike fungal strands from infected roots to
healthy roots through root to root contact. Initial
infections of the pathogen have been presumed to be
via airborne basidiospores released from the gills on
the undersides of the mushrooms, but this method has
never been demonstrated. The removal of infected
plants does not eradicate the mushroom root rot
disease. The fungus survives saprophytically in
stumps and dead roots and may cause infections for
Infected plants may not show any visible
symptoms until a major portion of the root system is
affected. The fungus can remain on the root system
feeding without obvious injury to the plant. If plants
are grown under optimum conditions with little stress,
the plant can withstand the damage to the roots
caused by Armillaria by continuously producing new,
uninfected roots. However, if environmental
conditions are not optimal and the plant is stressed,
the pathogen can cause extensive damage leading to
the rapid decline and eventual death of the plant
without exhibiting obvious symptoms. In some
instances where the environment is optimal for the
fungus, rapid colonization and spread onto new and
existing roots will cause a quick decline of a plant
even though growing conditions are optimal for plant
growth and development.
Preventative measures to manage mushroom root
rot such as the removal of diseased trees and their
root system before re-planting should be taken in
order to reduce the possibility of future infections.
Cultural practices to maintain vigorously growing
plants help to reduce the colonization of the fungus.
These practices include keeping root damage to a
minimum when planting or transplanting, planting at
proper depths so that the root collar is not buried in
the soil, keeping mulch away from the root collar,
and maintaining an optimum growing environment
(i.e., soil fertility, pH, irrigation) to alleviate any
stresses to the plant. Currently, there are no known
effective fungicides registered for the control of
mushroom root rot on guava.
Thread blight occurs on a wide range of host
plants. The disease develops primarily in the spring
and summer months when warm, humid conditions
Typical symptoms consist of circular to
sub-circular leaf spots, tan to brown in color with
alternating light and dark concentric rings dispersed
throughout the canopy leaf spots eventually coalesce,
resulting in a blight appearance. Leaves may be stuck
together with tan to brown mycelium originating
from the leaf margin.
2006 Florida Plant Disease Management Guide: Guava (Psidium guaiava) 5
Leaves, either on a new flush or an older flush,
may appear water-soaked, necrotic, and the disease
may eventually defoliate the plant. Leaves are held
onto twigs by coarse brown threads of the causal
pathogen. The fungus can invade leaves and twigs
causing a dieback. It has been observed under warm,
humid conditions, that the interior of the plant canopy
is affected by the web blight disease (Benson and
Jones 2001). Distribution of the disease is likely
when plants are in close proximity to each other under
Rhizoctonia solani Kuen (syn. Thanatephorus
cucumeris (A. B. Frank)) Donk, teleomorph, is a
hyphomycete with sterile mycelia. Hyphae of
mycelium are brown with long cells and septa of
branch set off from main hypha (Barnett and Hunter
1998). R. solani can be isolated from infected leaves
cultured on growing media. Media used for mass
hyphal transfers include Flowers media (FM),
Acidified Potato Dextrose Agar (APDA), Quarter
Strength Acidified Potato Dextrose Agar (QAPDA)
and Water Agar (WA). The morphological
characteristics of the pathogen grown on the media
were indicative of a Rhizoctonia species. In order to
speciate the Rhizoctonia pathogen, a nuclear staining
technique was utilized to determine if the particular
species was binucleate or multinucleate (Tu and
Kimbrough 1973). Following the technique of Tu
and Kimbrough (1973), it was determined that the
pathogen was multinucleate, and confirming it as R.
Disease Cycle and Epidemiology
Rhizoctonia spp. are among the most diverse of
plant pathogenic fungi, causing root, stem, and foliar
diseases of many subtropical and tropical hosts.
Typically, Rhizoctonia spp. attack plants at the soil
line causing root and stem rots. This pathogen can
attack leaves as well, and is especially severe when
trees are planted close together and the foliage
remains moist for prolonged periods.
On guava, disease development can occur in less
than one week. When humidity is high, the web-like
brown mycelium of the fungus can cover portions of
the foliage that are infected. The pathogen may
invade the canopy from the ground level by means of
mycelial webbing (Schubert and El-Gholl 1995).
Under favorable conditions, the pathogen may
produce a thin grayish or tannish-white hymenial
layer consisting of mycelium, basidia and
basidiospores of the telemorph, Thanatephorus
cucumeris, on the zonate lesions (Schubert and
El-Gholl 1995). The lesions produced may appear
water-soaked and discolored (Benson and Jones
2001). The characteristic feature of R. solani is the
tan to brown colored mycelium produced on the
margins of infected leaves that will cause necrotic
and abscised leaves to web or stick together. If the
infection is severe, the center of the plant may
become defoliated. Rhizoctonia may survive as
hyphae and sclerotia associated with infected crop
debris (Benson and Jones 2001). Once the pathogen
is established in a plant canopy, it may spread to
adjacent plants if plants are spaced in close proximity
to each other. It has been observed that under moist
conditions leaf infection occurs within 48 hours of
inoculation (Benson 1993).
Cultural practices such as increased plant to plant
spacing to promote air circulation, avoidance of
overhead irrigation and irrigation regimens that
extend leaf wetness periods, good sanitation practices
(removal of infected plant debris, management of
weeds that may be potential hosts, standing water,
etc.) and proper nutrient management plans to
maintain vigorous plants.
Fungicides may be used in a preventive or
curative manner if infection is likely or present.
Available fungicides for the use on Guava in Florida
are found in Table 1.
Guava Diseases Caused by Nonfungal Agents
Algal Leaf Spot
Algal leaf spot occurs on a wide range of
tropical fruit species. The presence of the pathogen
on the leaf reduces the photosynthetic leaf area
thereby affecting the growth of the tree.
Susceptibility to the disease is greatest when
2006 Florida Plant Disease Management Guide: Guava (Psidium guajava) 6
environmental conditions such as poor soil,
overcrowding and weed pressure are present. The
presence of insects, mites and other foliar diseases
may further increase the severity of the disease.
Disease symptoms are exhibited on both abaxial
and adaxial leaf surfaces as orange, rust-colored,
dense silky tufts ranging from 5 to 8 mm in diameter.
Upon scraping away these spots, a thin, grayish white
to dark-colored, necrotic crust remains on the leaf.
These spots usually come together to form large
irregular patches on a leaf. As the spots mature they
take on a dull, grayish green color. Twigs and
branches are also affected causing the bark to crack
due to the growth and expansion of the pathogens
filaments into the cortical tissues of the host.
The green alga, Cephaleuros virescens Kunze, is
the causal pathogen of this disease. The orange color
of spots is the thallus of the alga. The structure of the
thallus consists of a subcuticular expanse of cells
from which erect, bristle-like branches arise. The
apical parts of some cells swell to form enlarged
support cells that produce several stalked, terminal or
ovoid sporangia that are 30 x 24 pm. The stalked cell
may be bent. The sporangia of the alga produce
biflagellate zoospores. The alga reproduces sexually
via the production of flask-shaped gametangia in the
thallus disk. The biflagellate gametes (8 32) are
released when free water is present. Once released,
they fuse into pairs giving rise to dwarf sporophytes,
which in turn produce microsporangia that bear
Disease Cycle and Epidemiology
Algal leaf spots proliferate under wet or humid
conditions within the trees canopy. Infectious
propagules such as sporangia and biflagellate
zoospores are disseminated by water splash and wind;
biflagellate zoospores are the primary infection stage
of the pathogen. Quadriflagellate spores have not yet
been identified as infection sources.
Algal leaf spot can be reduced by maintaining
tree vigor with cultural techniques such as proper
fertilization and irrigation, proper pruning to enhance
air circulation within the canopy and sunlight
penetration, managing weeds and wider tree spacing.
Managing insect, mite and other foliar diseases
increases tree vigor and lessens susceptibility to this
disease. If chemical control is warranted, periodic
applications of a copper-based fungicide will control
the alga (Table 1).
Nematodes are widespread and problematic in
guava producing areas. Depending on soil type,
different nematode species can proliferate and cause
disease. A general decline in tree vigor is observed in
response to high nematode populations.
Aboveground symptoms associated with
nematode infection include chlorosis, stunting,
premature wilting, and nutrient deficiencies. Below
the ground, a reduction of fine root densities and root
distortion is observed.
Causal nematode agents include reniform
nematode (Rotylenchulus reniformis), burrowing
nematode (Radopholus similis), ring nematode
(Hemicriconemoides magniferae) and root-knot
nematode (Meloidogyne spp.). While many species
(M. incognita, M arenaria, M javanica, and M
hapla) of root-knot nematode cause disease in guava
producing areas worldwide, Meloidogyne incognita,
of races 1 and 2 are pests of guava in Florida.
The use of nematode free planting stock is the
best control method. In Florida, there are no
currently registered nematicides for the use on
2006 Florida Plant Disease Management Guide: Guava (Psidium guaiava) 7
Alfieri, S.A., Jr., K.R. Langdon, J.W.
Kimbrough, N.E. El-Gholl, and C. Wehlburg. 1994.
Diseases and disorders of plants in Florida. Florida
Department of Agriculture & Consumer Services,
Division of Plant Industry, Gainesville, FL. Bulletin
14. 653 p.
Alfenas, A.C., Zauza, E.A.V., Wingfeld, M.J.,
Roux, J., and Glen, M. 2005. Heteropyxis natalensis,
a new host ofPuccinia psidii rust. Australas. P1.
Pathol. 34: 285 286.
Ash III, E.C. and Barnard, E.L. (1994).
Mushroom Root Rot. Forest and Shade Tree Pests.
Division of Forestry. Leaflet number 11 (February).
Florida Department of Agriculture & Consumer
Barnett, H.L. and B.B. Hunter. 1998. Illustrated
Genera of Imperfect Fungi, 4th edition. APS Press, St.
Benson, M.D. 1993. Rhizoctonia Web Blight. P.
20-21. Compendium of Rhododendron Diseases.
APS Press, St. Paul, MN.
Benson, M.D. and R.K. Jones. 2001. Rhizoctonia
Web Blight. P. 63-64. Diseases of Woody
Ornamentals and Trees in Nurseries. APS Press, St.
Burnett H.C. and Schubert, T.S. 1985. Puccinia
psidii on Allspice and Related Plants. Plant Pathology
Circular No. 271 (May). Florida Department of
Agriculture & Consumer Services, Division of Plant
Industry, Gainesville, FL.
Chemsearch. 2006. Labels & MSDS.
Hemandez, J.R.. 27 February 2006. Invasive
Fungi. Puccinia psidii. Systematic Botany &
Mycology Laboratory, ARS, USDA. Retrieved May
3, 2006, from
Holliday, P. (1980). Fungus Diseases of
Tropical Crops. Cambridge University Press,
Cambridge. p. 401.
Laundon, G.F. and Waterson, J.M. (1965)
Pucciniapsidii. CMI Descriptions of Pathogenic
Fungi and Bacteria No. 56. Commonwealth
Mycological Institute, Kew, UK.
Leahy, R. (2004). Recent History of Puccinia
psidii on Myrtaceae in Florida. UF/IFAS Pest Alert
(January). Florida Department of Agriculture &
Consumer Services, Division of Plant Industry,
Schubert, T.S. and N.E. El-Gholl. 1995.
Rhizoctonia Leaf Spot ofRhaphiolepis. Plant
Pathology Circular No. 374 (Nov./Dec.). Florida
Department of Agriculture & Consumer Services,
Division of Plant Industry, Gainesville, FL.
Tu, C.C., and J.W. Kimbrough. 1973. A Rapid
Staining Technique for Rhizoctonia Solani and
Related Fungi. Mycologia, Vol. LXV, No. 4, pp. 941-
944, July- Aug.
2006 Florida Plant Disease Management Guide: Guava (Psidium guajava) 8
Table 1. Fungicides registered for use on guava in Florida.
Chemical Fungicide Maximum Rate/ Acre Minimum Disease or Pathogen Remarks2
Group' Application Season Daysto
Abound (azoxystrobin) 11 15.4 oz. 1.5 lbs. 0 Anthracnose Begin application prior
Cercospora & to disease
Pseudocercospora development and
Leaf Spot continue throughout
Rhizoctonia web blight the season on a 10-14
Guava Rust day schedule
Kocide and others 11 4.5 Ibs. 1 Anthracnose Make initial
(copper hydroxide) Algal Leaf Spot applications just before
Cercospora & flowering and repeat
Pseudocercospora on a weekly schedule
Leaf Spot until just before
Guava Rust harvest. Apply in
sufficient water for
Rootshield 5-12 Ibs./acre Pythium, Rhizoctonia, Root system disease
(Trichoderma Fusarium protectant
Serenade Max 1-3 Ibs./acre 0 Anthracnose May be applied up to
(Bacillus subtilis) __ Scab and on harvest day
Oxidate and others Curative: 128 General contact
(Hydrogen dioxide) fl.oz/100 gal biocide for numerous
of water pathogens
2006 Florida Plant Disease Management Guide: Guava (Psidium guajava) 9
Table 1. Fungicides registered for use on guava in Florida.
1Fungicide group (FRAC Code): Numbers (1-37) and letters (M, U, P) are used to distinguish the fungicide mode of action groups. All
fungicides within the same group (with same number or letter) indicate same active ingredient or similar mode of action. This information
must be considered for the fungicide resistance management decisions. M= Multi-site inhibitors, fungicide resistance risk is low; U= Recent
molecules with unknown mode of action; P= host plant defense inducers. Source: HYPERLINK "http://www.frac.infoP/ http://www.frac.info/
(FRAC = Fungicide Resistance Action Committee). Be sure to read a current product label before applying any chemicals,
information provided in this table applies only to Florida. Be sure to read a current product label before applying any chemical. The use of
brand names and any mention or listing of commercial products or services in the publication does not imply endorsement by the
University of Florida Cooperative Extension Service nor discrimination against similar products or services not mentioned.