Tar Spot Complex of Maize: Facts and Actions

Abstract

Tar spot is found throughout tropical and damp areas of the Americas, especially near riverbanks. The disease had been reported previously in Oaxaca but had not seriously affected yields, so farmers largely ignored it. Once a strong infection has appeared in a field, there is nothing farmers can do to save a crop. Partners including CIMMYT have identified resistant inbred maize lines and hybrids and are beginning to test them in farmers' fields where tar spot is a problem. Seed of the most resistant and best adapted will be increased and made available to farmers through leading seed providers. Partners are also developing and refining integrated management strategies for tar spot and providing farmers with relevant information about the disease, what causes it, and how to minimize its damage. This fact sheet contains detailed information about the disease and its causes, control recommendations for farmers, and lists of resistant maize inbred lines for breeders and seed producers. What is tar spot complex? Tar spot complex (TSC) is a maize disease that results from a synergistic interaction of three fungal species: Phyllachora maydis, Monographella maydis and the hypeparasite Coniothyrium phyllachorae. The disease occurs most often in cool and humid zones, especially in fields near riverbanks or with soils that hold moisture or flood. TSC was first reported in Mexico by Maublanc (1904).

Full text

Tar spot is found throughout tropical and damp areas of the Americas, especially near riverbanks. The
disease had been reported previously in Oaxaca but had not seriously aected yields, so farmers largely
ignored it. Once a strong infection has appeared in a eld, there is nothing farmers can do to save a crop.
Partners including CIMMYT have identied resistant inbred maize lines and hybrids and are beginning
to test them in farmers’ elds where tar spot is a problem. Seed of the most resistant and best adapted
will be increased and made available to farmers through leading seed providers. Partners are also
developing and rening integrated management strategies for tar spot and providing farmers with
relevant information about the disease, what causes it, and how to minimize its damage.
This fact sheet contains detailed information about the disease and its causes, control recommendations
for farmers, and lists of resistant maize inbred lines for breeders and seed producers.
What is tar spot complex?
Tar spot complex (TSC) is a maize disease that
results from a synergistic interaction of three fungal
species: Phyllachora maydis, Monographella maydis
and the hypeparasite Coniothyrium phyllachorae. The
disease occurs most often in cool and humid zones,
especially in elds near riverbanks or with soils that
hold moisture or ood. TSC was rst reported in
Mexico by Maublanc (1904).
TSC development and symptoms
TSC occurs commonly in moderately cool and
humid tropical and subtropical mountainous areas
of 1,300 to 2,300 meters above sea level (masl). The
disease starts with infection by P. maydis when
the plant has 8-10 leaves but becomes notable and
devastating after owering stage, with the presence
Tar Spot
Complex
of Maize: Facts and Actions
After a week of heavy fog in the rst week of October 2012, a
fungal disease known as tar spot complex struck maize elds
across large areas in the southeastern Mexican state of Oaxaca. The
disease cut farmers’ yields by 70-90% and completely destroyed
some crops. Maize landraces—which comprise four-fths of the
maize grown in Oaxaca—were most severely aected.
of M. maydis. The following conditions favor TSC
development:
• Monthly mean temperatures of 17-22°C, with at least
7 hours per night of leaf wetness and
- relative humidity above 75%, or
- 10 to 20 foggy days per month, or
- a minimum monthly rainfall of 150 mm, and
• 1,800-1,900 hours of sunlight per year (Hock et al.
1989).
The presence of free moisture on leaves at night and in
the mornings favors infection and establishment, as do
continuous cultivation of maize (it provides a constant
source of disease inoculum), high levels of fertilization
(especially nitrogen), use of susceptible maize varieties,
and low light intensity (Pereyda-Hernandez et al. 2009).
For more information:
• George Mahuku, maize pathologist (g.mahuku@cgiar.org).
• Rosemary Shrestha, data coordinator (R.Shrestha2@cgiar.org).
• Félix San Vicente, maize breeder (f.sanvicente@cgiar.org).

Symptoms. P. maydis induces dark, oval-to-round,
0.5-2.0 mm diameter lesions on leaves and forms
striations up to 10 mm long (Parbery 1967; Hanlin
1999). Initial symptoms are small, slightly-raised black
points randomly distributed on the leaf (Figure 1A
and 1B). The infection can be disseminated quickly
to the upper leaves and to other plants. Two or
three days after infection by P. maydis the lesions are
invaded by M. maydis, causing a light green elliptic
shaped halo surrounding each P. maydis lesion of
1-4 mm size, resulting in the ‘sheye’ symptom
associated with TSC disease (Figure 1C and 1D).
Under favorable conditions, P. maydis and M. maydis
act synergistically, lesions rapidly grow and coalesce
as the infection progresses until the whole leaf is
Figure 1. The appearance and development of tar spot complex on maize leaves.
Note the characteristic ‘sh-eye’ symptoms.
A B C D E
Figure 2. A eld with heavy tar spot complex symptoms, a common sight in elds
visited in Oaxaca in 2012.
blighted (Figure 1E) and suers premature drying (Figure
2). Watch especially for the appearance of the small
black lesions, which indicate the presence and initial
development of the disease (Figure 1B).
Impact of TSC on maize yields
Impact of TSC on maize yields depends on the time of
infection and environmental conditions. On susceptible
genotypes and when conditions for disease development
are conducive, the plant can be completely blighted in 8
to 14 days after infection, as lesions coalesce and P. maydis
produces a toxin that rapidly kills plant tissue. If infection
and disease onset happen early and before ears start to ll
this can result in poor seed set and shriveled, light-weight
grains (Figure 3C), which may germinate prematurely on
the cob (Figure 3A) and result in yield losses greater than
50% (Figure 3B) (Hock et al. 1989).

TSC in Latin America
TSC was rst reported in Mexico and has constantly
been observed at altitudes of 1,300-2,000 masl and also
in the tropical and subtropical maize-producing areas.
The disease is a signicant threat on more than 800,000
hectares in the Mexican states of Jalisco, Michoacán,
Nayarit, Veracruz, Oaxaca, Chiapas, and Guerrero. In
addition to cutting grain yields, TSC has been reported
to reduce fodder quality. When infection occurs before
owering in very susceptible varieties, grain and fodder
losses can reach 100%. During 2001-05, the disease
caused severe losses in grain yield in approximately
40% of the 3,100 hectares of maize grown in the valley
of Mochitlán, Guerrero; total losses were reported for
600 hectares of maize in the municipality of Tixtla,
Guerrero, in 2005; in 2007 the disease appeared in more
than 10 municipalities of Guerrero (González et al.
2008). In Oaxaca, heavy disease incidence and severity
were observed in 2012, with estimated yield losses in
excess of 50%. Signicant economic losses from the
disease have also been reported for maize in
El Salvador, Guatemala, Colombia, Nicaragua,
Honduras, Costa Rica, Panama, and many other Latin
American countries (Lopez et al. 2011).
TSC management
Integrated control approaches for TSC include
appropriate crop management practices and use of
resistant varieties. It is important to identify initial
symptoms very early, by way of constant monitoring
of elds starting when plants are at the 8-leaf stage
until post-owering and grain lling stages. These are
Figure 3. Eects of tar spot complex disease on maize ears: (A) poorly-lled ear with premature
germination of grain on the cob; (B) a poorly-lled ear in a crop in Oaxaca, Mexico; and (C) close-up of
an ear with shriveled grains.
A B C
the growth stages when TSC has the greatest impact.
Recommended practices include the following:
• Obtain and use seed of TSC resistant varieties. The
Mexican National Institute of Forestry, Agriculture,
and Livestock Research (INIFAP) has developed
several resistant hybrids (H-377, H-318, H-562, and
H-563; Gonzalez Camarillo 2005) (Figure 4).
• Plant the entire crop early or on time. Avoid
staggered planting, as earlier plantings may be a
source of inoculum for later plantings. Late-planted
crops usually show high disease incidence.
• Reduce pathogen inoculum sources by eliminating
crop residues and stubble, to reduce sources of
pathogen inoculum.
• Avoid using elds with known incidences of TSC or
that are close to river banks.
• Rotate maize with crops on which the pathogen
will not grow; these include common bean and
horticulture crops.
• On elds where the disease has previously
appeared, constantly monitor the crop, starting
about 40 days after emergence or when the crop has
8 leaves.
• Follow recommended planting densities; higher
densities (say, more than 75,000 plants per hectare)
favor disease development.
• Use recommended dosages of nitrogen fertilizer.
• Apply contact or systemic fungicides as soon as
disease symptoms appear.

Resistant inbred lines and hybrids
Through evaluation under natural disease pressure
during winter cycle at its Agua Fría experiment station
(90 masl) in Puebla, Mexico, CIMMYT has identied
promising elite inbred maize lines (Tables 1 and 2) of
both white and yellow backgrounds, and veried their
resistance in subsequent tests under severe disease
pressure in Guerrero and Veracruz states. Seed of the
lines is available for use by interested breeders.
Tests of experimental, pre-commercial, and commercial
hybrids under natural disease pressure at multiple
locations in Mexico during summer 2012 revealed a
number of resistant hybrids (Table 3-5). Experimental
hybrids from CIMMYT that have shown good levels
of resistance in tests under natural disease pressure in
Guatemala and Honduras include CML264/CML269//
CLWN247 and CLRCW96/CLRCW95//CLWN47; these
are being validated in Mexico.
Chemical control of TSC
Fungicides that have been reported to be eective in
controlling TSC include propiconazole, carbendazim,
benzimidazoles, a mixture of poxiconalzole +
carbendazin, and benomyl (Gonzalez Camarillo 2005).
Timely application of recommended fungicides at the
onset of the disease and two weeks after owering
are usually sucient to control TSC. Application rates
should follow those recommended by the manufacturer.
Appropriate protective clothing (e.g. gloves, eyeglasses,
masks, respirators, and disposable overalls, etc.) should
be used when handling fungicides.
Figure 4. A resistant
hybrid (H-377, developed
by INIFAP-Mexico) and
a susceptible variety
OCELOTE planted 4 days
apart. The susceptible variety
is completely devastated by
tar spot complex, while the
tolerant hybrid shows few
signs of the disease.
References
Gómez Montiel N.O., M. Sierra Macías, M. González
Camarillo, M.A. Cantú Almaguer, A. Ramírez Fonseca,
J.J. Wong Pérez, and M. Manjarrez Salgado. 2005. H-563,
híbrido de maíz de alta productividad y resistente al
complejo “Mancha de asfalto”. Folleto Técnico Núm. 12.
Instituto Nacional de Investigaciones Forestales, Agrícolas
y Pecuarias (INIFAP). Campo Experimental Iguala,
Guerrero.
Gómez Montiel, N.O., M. Sierra-Macías, M. González
Camarillo, M.A. Cantú Almaguer, A. Ramírez Fonseca,
J.J. Wong Pérez, M. Manjarrez Salgado, J.L. Ramírez Díaz,
and A. Espinosa Calderón. 2008. H-562, híbrido de maíz
de alto rendimiento para el trópico húmedo y seco de
México. Agric. Téc. Méx. 34 (1): 101-105.
González Camarillo, M. Nuevos métodos de control de
la “Mancha de Asfalto” en Maíz. Fichas tecnológicas
sistema producto, Instituto Nacional de Investigaciones
Forestales, Agrícolas y Pecuarias (INIFAP). Accessed
on 21 April 2013 at http://utep.inifap.gob.mx/
tecnologias/11.%20Agr%C3%ADcolas/NUEVOS%20
M%C3%89TODOS%20DE%20CONTROL%20
DE%20LA%20%E2%80%9CMANCHA%20DE%20
ASFALTO%E2%80%9DEN%20MA%C3%8DZ.pdf.
Hanlin, R.T. 1999. Combined Keys to Illustrated Genera of
Ascomycetes. Vol. I and II. APS Press. St. Paul. Minnesota.
pp: 63–64.
Hock, J., J. Kranz, and B.L. Renfro. 1989. El complejo ‘mancha
de asfalto’ de maíz: Su distribucción geográca, requisitos
ambientales e importancia económica en México. Rev Mex
Fitopatol 7:129-135.
Hock, J., J. Kranz, and B.L. Renfro. 1995. Studies on the
epidemiology of the tar spot disease complex of maize in
Mexico. Plant Pathol. 44:490-502.
Lopez, C., O. Salazar, R. Dax, M. Osorio, C. Calderon, H.
Cabrera, A. Ferruno, A. Viana, and D. Saavedra. 2011.
Reconocimiento en campo de la mancha de asfalto en el
cultivo de maíz. http://www.redsicta.org/PDF_Files/
manchaNegra.pdf

Table 2. Responses of selected elite white QPM lines and elite white and yellow lines under natural TSC infection at
Agua
Fría
experiment CIMMYT lowland tropical station, 2011.
Elite white QPM lines TSC rating Elite white lines TSC rating Elite yellow lines TSC rating
CLQRCWQ129 1.5 CLQRCWQ129 1.5 CLYN227 1.3
CLWQ235 2.0 CLWQ225 2.0 CML451 1.3
CLWQ229 2.0 CLQRCWQ97 2.0 CLYN217 1.3
CLQRCWQ97 2.0 CLWQ235 2.0 CLYN225 1.5
CML491 2.0 CLQRCWQ120 2.0 CLYN233 1.5
CLWQ225 2.0 CLQRCWQ121 2.0 CLYN226 1.7
CLQRCWQ121 2.0 CLWQ245 2.0 CLYN214 1.8
CLQRCWQ120 2.0 CLWQ229 2.0 CLYN234 1.8
CLWQ245 2.0 CML491 2.0 CLYN215 2.0
Table 1. Responses of selected maize inbred lines to tar spot complex under natural infection at CIMMYT’s
experiment station in Agua Fría, Puebla, 2011-2012.
TSC rating
Name Pedigree 2011 2012 Grain yield (t/ha)
DTMA-189 CL-02520=P25C6H37-1-1-1-B-2-1-2-BBB-B 1.4 1.2 2.34
DTMA-21 [CML312/[TUXPSEQ]C1F2/P49-SR]F2-45-3-2-1-BB//INTA-
F2-192-2-1-1-1-BBBB]-1-5-1-1-2-BB-B 1.5 1.2 0.60
DTMA-27 P502-SRc0-F2-54-2-2-1-B-B 1.5 1.0 0.56
DTMA-109 [M37W/ZM607#bF37sr-2-3sr-6-2-X]-8-2-X-1-BB-B-xP84c1
F27-4-3-3-B-1-B] F29-1-1-1-7 x [KILIMA ST94A]-30/MSV-03-
2-10-B-1-B-B-xP84c1 F27-4-1-6-B-5-B]-1-3-B/CML312SR]-1-1 1.5 1.5 1.29
DTMA-11 CIMCALI8843/S9243-BB-#-B-5-1-BB-4-1-3 1.5 1.0 1.99
DTMA-158 CML-329/MBR c2 am F14-2-BBBB 1.6 1.0 2.37
DTMA-282 DTPYC9-F69-3-5-1-1-B-B 1.7 1.0 1.15
DTMA-147 CML-311 1.8 . 2.09
DTMA-17 [CML312/CML445//[TUXPSEQ]C1F2/P49-SR]F2-45-3-2-1-BBB]-
1-2-1-1-2-BBB-B 2.0 2.0 1.75
DTMA-93 CML311/MBR C3 Bc F3-1-1-1-B-B-B-B-B 2.0 1.5 3.85
Note: Tar spot rating is done on a 1-5 scale, where
1= No or very few lesions all on leaves below the ear,
2 = Resistant. Moderate lesions on leaves below the ear covering approximately 10 to 25% of the leaf area aected.
3 = Moderately susceptible. Most of the leaf are below ear is necrotic and many lesions above ear coalescing. Percentage of leaf
area aected varying from 25-50%.
4 = Susceptible. No green tissue on leaves below the ear, many or severe lesions development on all but the uppermost leaves,
which may have a few lesions, lesions have coalesced and 50 – 80% of leaf area blighted.
5 = Highly susceptible. All leaves are dead, no green leaf tissue remaining or disease symptoms on >80% of the leaf surface.
Maublanc, A. 1904. Espéces nouvelles de Champignons inferius.
Bull. Soc. Myc. Fr. 20: 72.
Parbery, D. G. 1967. Studies on graminicolous species of
Phyllachora Nke. Aust. J. Bot. 15: 271–375.
Pereyda-Hernández, J., J. Hernández-Morales, J. Sergio
Sandoval-Islas, S. Aranda-Ocampo, C. De Leon, and N.
Gómez-Montiel. 2009. Etiology and management of tar
spot (Phyllachora maydis Maubl.) of maize in Guerrero state
of Mexico. Agrociencia 43: 511-519.

Table 4. Responses of yellow commercial and experimental subtropical hybrids under natural infection at two sites
in Oaxaca in 2012.
TSC rating Multi-location
Hybrid Pedigree Zaachila Santiago Etla performance average Hybrid type
HSTY-07 P-2844 1.5 1.5 1.5 Commercial
HSTY-02 GSG-104 1.5 2.5 2.0 Commercial
HSTY-03 XP-0831 3.0 2.5 2.8 Pre-commercial
HSTY-10 ZR-24 3.5 2.5 3.0 Commercial
HSTY-12 COMITECA AM. QPM 3.0 3.0 3.0 Experimental
Table 5. Responses of yellow commercial and experimental subtropical hybrids under natural
infection at two sites in Oaxaca.
TSC rating Multi-location
Hybrid Santiago Etla Zaachila performance average Hybrid type
MARLIN 1.5 1.5 1.5 Commercial
REGA-010 2.0 2.0 2.0 Commercial
P3055W 2.5 2.0 2.3 Commercial
GLADIADOR 2.0 3.0 2.5 Commercial
H374C 2.5 3.0 2.8 Commercial
AS-1501 2.5 3.0 2.8 Pre-commercial
REGA-020 2.5 3.0 2.8 Commercial
H-318 3.0 2.5 2.8 Commercial
Table 3. Responses of elite commercial and experimental hybrids under natural disease pressure at two sites in Chiapas,
in 2012.
Jesús María Garza, Multi-location
Villa Flores: La Esperanza, performance
Hybrid Grain color (Frailesca) Chiapa de Corso average Hybrid type
NB7 White 1.8 1.5 1.7 Commercial
CLRCW100/CLRCW96//CML494 White 2.0 1.5 1.8 Experimental
SAN PEDRO 2423 White 1.5 2.0 1.8 Experimental
CML498/CLRCW500//CML494 White 2.5 1.5 2.0 Experimental
H520 White 3.5 1.0 2.3 Commercial
DK7088 Yellow 2.5 1.5 2.0 Commercial
CL02450/CLRCY041//CML451 Yellow 2.8 1.5 2.2 Experimental
CLRCY044/CLRCY039//CL02450 Yellow 3.3 1.5 2.4 Experimental
TYDC/G26 Yellow 3.5 1.5 2.5 Experimental
Funds for this work were generously provided by Mexico’s Secretariat of Agriculture,
Livestock, Rural Development, Fisheries and Food (SAGARPA) through the program
“MasAgro-the Sustainable Modernization of Traditional Agriculture”