New fungicide controls rice sheath blight

Research Journal of Agricultural Sciences 2012, 3(2): 500-505
A New Carboxynilide Group Fungicide against Paddy Sheath Blight
M K Prasanna Kumar, D K Sidde Gowda, K T Pandurange Gowda and K Vishwanath
Zonal Agricultural Research Station, VC Farm, (UAS, GKVK, Bangalore) Mandya – 571 504, Karnataka, India
e-mail: babu_prasanna@rediffmail.com
A B S T R A C T
Thifluzamide, a new fungicide of carboxynilide group was tested for the efficacy against rice sheath blight during
2005, 2006 and 2009. Among, different test concentrations, Thifluzamide 24% SC @ 90 and 110g ai/ha was found
effective in reducing the disease severity and increasing the yield. Carboxinililde group fungicide was found
effective both as preventive and curative activity without any symptoms of phytotoxicity such as, vein clearing,
necrosis, epinasty, hyponasty etc on rice plants. The cost of managing the disease by two applications is covered by
the extra yield achieved due to suppression of the disease, where it was found significantly superior to the
standards. Residues of Thifluzamide and its metabolite in grain, straw and soil were found below the quantifiable
limit at the test doses.
Key words: Thifluzamide, Carboxynilide, Sheath blight, Rhizoctonia solani
Sheath blight, Rhizoctonia solani Kuhn (Teleomorph:
Thanatophorus cucumeris (Fran) Donk. has assumed the
status of economically important disease in paddy, and has
become a major constraint to rice production during the last
two decades (Kobayashi et al. 1997). The disease is
prevalent in all rice growing countries especially in South
and Southeast Asia and causes significant yield losses
(Premalatha 1990, Roy 1993, Rajan and Naidu 1986,
Ramakrishnan 1971). Yield loss up to 50% has been
recorded in susceptible rice cultivars when all the leaf
sheaths and leaf blades were infected (Lee and Rush 1983).
The emergence of R. solani as economically important rice
pathogen has been attributed to the intensification of rice-
cropping systems with the development of new short-stature,
high-tillering, high-yielding varieties, high plant densities
and increased level of fertilizers and other inputs (Chahal et
al. 2003, Siddiq 1999) and these factors promote disease
spread by providing favourable micro climatic condition due
to dense leaf canopy with an increase leaf-to-leaf and leaf-
to-sheath contact (Savary et al. 1995). Both seedlings and
adult plants are equally affected but loss is much more when
the disease appears in seedlings. The older plants are
attacked in flooded conditions and swampy rice fields
(Dodman and Flentje 1970, Kannaiyan 1987, Shimamoto
1995). The infection and spread of disease before the flag
leaf stage revealed 20% grain loss. Further, a strong
relationship between the severity of symptom and yield
reduction was reported among cultivars (Marchetti and
Bollchi 1991). S
Sheath blight can be effectively controlled with the
application of systemic fungicides. However, bio-fungicides
and resistant varieties are the other options of control
management but, are not at par with chemical control.
These fungicides are very popular and are at the peak of its
usage which may lead to reduced residual period and
efficacy due to increased virulence of R. solani.
Thifluzamide is a member of the carboxamide class of
fungicides which is single-site inhibitors of the succinate
ubiquinone reductase or succinate dehydrigenase (Sdh)
complex in the respiratory chain (FRAC 2007) interfere with
fungal respiration via their inhibitory effect on succinate
dehydrogenase within the tricarboxylic acid cycle. (O’Reilly
1995). This compound was reported effective against
Basidiomycete fungi in particular along with efficacy on
some Ascomycetes and Rhizoctonia solani. This molecule is
registered for use in rice, turf, potatoes, coffee and
strawberries in Brazil, Mexico, Colombia, Venezuela, Japan,
Korea, China and Vietnam. Since, no fungicide has been
registered with this unique modes of action for the control of
sheath blight of paddy, Thifluzamide can fit into resistance
management system by integrating in spray schedules in
potential rice growing tracts. Hence, the present study was
conducted to characterize Thifluzamide 24 % SC under field
conditions against Rhizoctonia solani.
MATERIALS AND METHODS
The experiment was laid out in red sandy loam soils
with unique soil properties (pH 5.9 to 6.2, 0.30% organic
matter, 25.0kg ha-1
of available N, 24.23kg ha-1
of P2O5 and
215.55kg ha-1
of available K2O). The plots were flooded
with water and ploughed until any soil aggregates were
broken up. Excess water was drained out and the field was
partitioned into 7 blocks. The efficacy of the fungicide
against sheath blight was investigated under field conditions
at Zonal Agricultural Research Station, Mandya, Karnataka
during Kharif 2005, 2006 and 2009. The experiment was
laid out in a randomized block design with seven treatments
replicated four times. Uniform plant population was
maintained for each plot, with spacing of 20 × 10cm
between rows and plants, respectively. The experimental site
was selected based on intensive cultivation of rice where,
sheath blight disease a major yield constraints to the
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farmers. Treatments consisted of a rice plant (cv. IR-64)
sprayed with different doses of Thifluzamide 24% SC (75.
90, 110g ai/ha) along with recommended national standard
fungicides. Two sprays of chemical with desired
concentration were given on 50th
, 65th
and 80th
days after
planting (DAP). The first spray was applied as prophylactic
spray at jointing stage and second spray was applied as
curative sprays when the third to fourth leaf from the top
shows symptoms. For prophylactic trails fungicides were
sprayed before disease appearance and curative trials were
taken at 37.5% disease incidence. The causal organism was
artificially built up at tillering stage using the fresh sheath
blight infected bits on the rice seedlings by placing between
the tillers just above the water line at 38 DAP. The
sclertotial bodies produced by the isolated cultures of R.
solani were also used for inoculation at the sheath region
near water level.
A popular sheath blight susceptible variety, IR-64 was
used as check in all three years. The disease assessment was
carried out at 14 days after fungicide application. In each
trial two observations were recorded. The first observation
was made soon after prophylactic spray and second after
curative spray. The disease severities were subjected for 0-9
scale using standard evaluation system for rice developed by
International Rice Research Institute (SES 2002). Further,
the disease severity was calculated using the formula.
Subsequently, the data on disease severity and yield
parameters were collected and were subjected to appropriate
statistical analysis:
0 - No infection
1 - Vertical spread of the lesions up to 20% of plant height
3 - Vertical spread of the lesions 21 - 30% of plant height
9 - Vertical spread of the lesions > 65%of plant height
Disease
severity % =
Sum of disease grades × No. of infected tillers/ hill
× 100Total No. of Tillers × Max. disease grades × No.
of tillers assessed
In each treatment, ten plants selected at random. The
total number of leaves and those showing phytotoxicity
parameters viz leaf injury, wilting, vein clearing, necrosis,
epinasty hyponasty were recorded before spray, and at 3, 7,
and 15 days after spraying. Further, the percentage data
were subjected for 0-10 score (Fiebig 2002). The studies on
residues were carried out during 2005 at two doses (90 and
180g ai/ha) with an untreated control. The residue analysis
was done at International Institute of Biotechnology and
Toxicology (IIBAT), Chennai which was sponsored by
Nagarjuna Agrichemicals Limited. Five hundred grams of
test samples (straw, grain and soil) were collected and sent
to the IIBAT laboratory for residue analysis. The extraction
and column clean-up were done as per the protocol
developed by IIBAT. Shimadzu High Performance Liquid
Chromatograph system equipped with LC-10 ATvp pump
and SPD-10Vvp UV-VIS detector connected to CBM-101
module using CLASS-LC-10 software was used for
Thifluzamide analysis. The reference compound
Thifluzamide, Metabolite-1 (MON 24000-CH2OH) and
Metabolite-2 (MON 24000-COOH) supplied by Nagarjuna
Chemicals with a purity of 99.95%, 94.59 % and 100%,
respectively.
Table 1 Efficacy of new fungicide Thifluzamide 24% SC as prophylactic spray against R. solani under field conditions
Treatments
Dose g
a. i/ha
2005 2006 2009
Disease
severity
% control
over untreated
Disease
severity
% control
over untreated
Disease
severity
% control over
Untreated
Thifluzamide 24% SC 60 18.67 (25.57) 60.28 22.33(28.19) 64.17 25.67 (30.41) 56.98
Thifluzamide 24% SC 75 14.67 (21.55) 68.79 23.00 (28.64) 63.10 24.67 (29.76) 58.66
Thifluzamide 24% SC 90 14.00 (21.97) 70.21 20.67 (26.97) 66.84 22.33 (28.20) 62.57
Thifluzamide 24% SC 110 12.00 (20.22) 74.47 19.33 (26.03) 68.98 21.33 (27.50) 64.25
Validamycin 3% L (St.I) 37.5 25.33 (30.16) 46.10 40.00 (39.22) 35.83 28.00 (31.93) 53.07
Hexaconazole 5 EC (St.II) 50 22.67 (28.38) 51.77 32.67 (34.84) 47.59 25.33 (30.21) 57.54
Untreated control - 47.00 (43.26) 0.00 62.33 (52.17) 0.00 59.67 (50.58) 0.00
SE m± 1.40 - 1.33 - 0.74 -
CD @ p=0.05 4.27 - 3.45 - 2.26 -
CV % 8.76 5.76 3.9
Figures in parenthesis are Arcsine transformed; St.I: Standard-I, St.II: Standard-II
For calibrating the limit of detection, different
concentrations of Thifluzamide and its metabolites (5.0 -0.5
ppm) were prepared in residue grade methanol by diluting
the stock solution which, was used for injecting to HPLC
along with standards. A calibration curve was plotted for
concentration of the standard injected against area observed.
The lowest limit of detection (LOD) was established as
0.05ppm for Thifluzamide and its metabolites. Residual
content was calculated with the formula:
Residue content (µg/g) = A × B × C
D × E
Where, A-Peak area of samples (µV-sec)
B-Volume of sample (ml)
C-Concentration of the standard (µg/ml)
D- Peak area of standard (µV-sec)
E- Weight of the sample (g)
RESULTS AND DISCUSSION
Sheath blight (R. solani) infection dominated during all
the years. The infection was severe in 2006 and 2009 when
it was promoted by high relative humidity and high
Kumar et al.
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temperature. During the study, disease severity was 47.0,
62.33 and 59.67% which helped in characterization of the
new fungicide. The increased disease pressure in the present
study was attributed to natural incidence and artificial
inoculation of the pathogen. In all the three field trials
Thifluzamide 24% SC provided excellent control of sheath
blight with exceptional long lasting activity against sheath
blight.
Table 2 Impact of new fungicide Thifluzamide 24% SC as curative spray rice sheath blight disease and yield
Treatments
Dose
g a.
i/ha
2005 2006 2009
Disease
severity
% control
over untreated
Yield
kg/ha
Disease
Severity
% control over
untreated
Yield
kg/ha
Disease
severity
% control
over untreated
Yield
kg/ha
Thifluzamide 24% SC 60
14.50
(21.94)
53.23 3967
18.75
(25.62)
53.13 4451
17.44
(24.67)
58.54 4642
14.50
(21.77)
53.23 4094
11.75
(19.98)
70.63 5002
10.88
(19.24)
74.15 4870
11.00
(19.27)
64.52 4105
10.00
(18.39)
75.00 4843
9.13
(17.57)
78.31 5043
8.50
(16.87)
72.58 4138
9.00
(17.43)
77.50 5379
8.31
(16.75)
80.24 5212
Validamycin 3% L (St.I) 37.5
10.50
(18.71)
66.13 3797
10.00
(18.43)
75.00 5010
11.63
(19.91)
72.36 4997
Hexacomazole 5 EC
(ST.II)
50
10.50
(18.71)
66.13 3627
10.00
(18.43)
75.00 4740
11.94
(20.16)
71.62 4970
Untreated control -
31.00
(28.68)
0.00 3145
40.00
(39.21)
0.00 4179
42.06
(40.42)
0.00 4342
SE m± 1.5 124.43 0.67 123.9 0.61 100.1
CD @ p=0.05 4.41 369.55 1.98 367.8 1.80 308.6
CV % 13.78 6.48 5.93 5.2 5.37 3.6
Figures in parenthesis are Arcsine transformed; St.I: Standard-I, St.II: Standard-II
Table 3 Cost Benefit ratio of Thifluzamide 24% SC application against sheath blight of paddy
Treatments Dose g
a i/ha
Grain yield
Kg/ha
Total returns
(Rs.)
B:C
ratio
Marginal
cost (Rs.)
Total cost
(Rs.)
Total returns
(Rs.)
Marginal
returns (Rs.)
Thifluzamide 24% SC 60 3967 43637 1.897 1000 23000 29679.000 9042
Thifluzamide 24% SC 75 4094 45034 1.937 1248 23248 32225.000 10439
Thifluzamide 24% SC 90 4105 45155 1.921 1500 23500 32215.000 10560
Thifluzamide 24% SC 110 4138 45518 1.910 1832 23832 32609.000 10923
Validamycin 3% L (St.I) 37.5 3797 41767 1.816 1000 23000 25939.000 7172
Hexaconazole 5 EC (ST.II) 50 3627 39897 1.750 800 22800 22399.000 5302
Untreated control 3145 34595 1.573 - 22000 12595.000 0.00
B:C ratio- benefit cost ratio; Total returns = Cost of grain @ Rs. 10/kg and straw Rs. 1/kg
Thifluzamide 24% SC @ 90 and 110g ai/ha was found
highly effective as prophylactic spray (14.0 and 12.0%) with
per cent disease control over untreated of 70.21 and 74.47,
respectively during kharif 2005. The untreated plots
recorded 47.0% disease severity, which confirms the disease
pressure during the experimentation. The standard
fungicides Validamycin 3% L @ 37.5g ai/ha and
Hexaconazole 5 EC @ 50g ai/ha were found inferior even
with Thifluzamide 24% SC @ 60g ai/ha. Similarly, during
kharif 2006 and 2009, the test fungicide @ 90 and 110g
ai/ha recorded a disease control 66.84 and 68.98, 62.57 and
64.25%, respectively over untreated (Table 1). The disease
in untreated plots was higher compared to kharif 2005 which
recorded 62.33 and 59.67%, respectively in 2006 and 2009.
The mean results proved the fact that Thifluzamide can give
good control of the disease as protective fungicide. As
expected, the fungicide sprayed after appearance of the
disease symptoms exhibited good control of the sheath
blight. Consistent results were observed in all the three trials
with application of thiflzamide @ 90 and 110g a.i./ha
recording 11.0 and 8.5, 10.0 and 9.0, 9.13 and 8.31 during
2005, 2006 and 2009, respectively. However, the standard
fungicides were also performed better as curative sprays.
The intensity of fungicide caused significant differentiation
in yields of tested varieties by treatment variants (Table 2).
Two applications of Thifluzamide 24% SC @ 90 and 110g
ai/ha revealed lower disease intensity with higher yields in
all the test years (Table 2).
Comparing the economic benefits of the extra yield
produced by application fungicide, in spite of recording
lower disease incidence it proved its effectiveness in
maximizing and stabilizing the net yield (4105 and 4138
kg/ha at 90 and 110g ai/ha). Taking into account, the cost of
cultivation of transplanted paddy ~Rs. 22,000/ acre and
grain cost Rs. 1000/quintal and straw cost Rs. 1000/tonnes.
The total cost of controlling sheath blight using
Carboxynilide Group Fungicide against Paddy Sheath Blight
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Thifluzamide @ 90 and 110g a i/ha is ~1500 and ~1832
which has given the marginal return of Rs. 10560 and
10923, respectively (Table 3).
Thifluzamide was tested for its phytotoxic effect on rice
at four different doses (60, 75, 90 and 110g a i/ha). All the
test doses did not cause any phytotoxic effect on rice viz leaf
injury, wilting, vein clearing, necrosis, epinasty and
hyponasty when applied as foliar spray after 3, 7 and 15
days. Analysis of paddy grains, straw and soil collected
from Mandya showed residues of Thifluzamide and its
metabolite below the quantifiable limit at the test doses. The
residue of the test chemical in paddy grains while similar
results were obtained in paddy straw and soil (Table 4).
Calibration of Thifluzamide and its metabolites were done
by injecting the sample concentration of 5.0 -0.05ppm and
response in area was plotted µV-sec and the data is
presented in table-5. Thifluzamide @ 90g a i/ha in paddy
grains were not found as per the standard MRL values of
WHO/FAO. While, under rule 65 of the prevention of Food
Adulteration Act 1965 of Government of India is 0.5 ppm.
The test chemical did not show any traces in paddy grains
and the proposed PHI was found to be 28 days.
Table 4 Residues of Thifluzamide and its metabolites in paddy grain
Treatment
Peak area (µV-sec)
Weight of
sample (g)
Volume
of sample
(ml)
Results (µg/g) Average residue (µg/g)
Thifluzamide
residue
MB-1 MB-2
Thifluzamide
residue
MB-1 MB-2
Thifluzamide
residue
MB-1 MB-2
T0 R1 ND ND ND 50 3 ND ND ND
ND ND NDT0 R2 ND ND ND 50 3 ND ND ND
Standard concentration of Thifluzamide : 0.05ppm-1126 (µV-sec); Standard concentration of metabolite-1 (MB-1): 0.05 ppm-794 (µV-sec)
Standard concentration of metabolilte-2 (MB-2) : 0.05 ppm-1283 (µV-sec); ND- Not detectable
Table 5 Calibration details of Thifluzamide and its metabolites
Injected
concentration(ppm)
(Thifluzamide and
Metabolites)
Response in area (µV-sec)
Thifluzamide Metabolite-1 Metabolite-2
5.0 104853 57182 120887
2.5 51813 28776 59072
1.0 20847 11409 23757
0.1 2286 1383 2538
0.05 1204 732 1316
Correlation coefficient: 0.999
Thifluzamide and its metabolites peak time report
obtained through chromatography indicated that there is an
increase in peak time with the decrease in area of response
which is directly related with metabolite/chemical
concentration. The peak time ranged between 3.624-3.782
for Metabolite I, 9.543-10.121 for Metabolite II and 11.835-
12.294 for Thifluzamide @ 5.0-0.05 µg/ml concentration,
respectively.
Intensive rice cultivation with no crop rotation and apt
seasonal weather factors has increased the occurrence of
sheath blight. Yield reduction due to disease infections can
avoid by chemical control measures. The chemical control
should be need based on by looking into the severity of the
disease, variety, and other abiotic factors. In future, the
inclination will most likely be towards management of
disease under integrated plant protection methods whereby
the fungicide dose and time of application are calculated
based on the resistance level of the variety, the prevailing
abiotic factors of the rice ecosystem (Sooväli and Koppel
2009). In UK, it has been found that fungicide treatment is
effective when the infection level is visually more than 5%
of leaf area (Cook et al. 1999) for instance, lowers intensity
infection and yield loss is found to be smaller than the cost
of fungicidal application.
In a rice ecosystem, in each season, more than one
disease is observed and hence new fungicidal groups like
oryzastrobin Qol are gaining importance as they are broad-
spectrum fungicides providing effective control against rice
sheath blight and blast (Stammler et al. 2007). However, the
broad spectrum fungicides may not give sufficient
protection when the disease severity is very high. At present
the ruling chemicals viz Hexaconazole, Propiconazole,
Validamycin, Carbendazim which are extensively used for
the management of sheath blight disease (Chien and Chu
1973, Wakae and Matsura 1975, Viswanathan and
Mariappan 1980a, b, Das and Mishra 1990, Van Eechout et
al. 1991). Further, laboratory studies on two isolates of R.
solani from rice and potato showed significant variation in
response to different concentrations of fungicides
(carbendazim, carboxin, pencycuron, Propiconazole and
Validamycin) (Thind and Aggarwal 2005). Lore et al.
(2005), Biswas (2002) evaluated and reported effectiveness
of new fungicide Pencycuron (Moncern 250 EC) against rice
sheath blight in Punjab and West Bengal. Our investigations
also revealed the effectiveness of Thifluzamide 24% SC
against R. solani causing sheath blight in paddy. To support
our results the data of 2005 trials were obtained from 16
locations which are part of All India Coordinated Research
Project, Directorate of Rice Research, Hyderabad including
Kumar et al.
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Mandya centre and locations across India were pooled (Fig
1). Thifluzamide @ 90 and 110g a i/ha was found highly
effective at all locations tested and strongly supports our
data conducted for three years.
Fig 1 Multi-location traits across the country on efficacy of
thifluzamide against sheath blight
Fig 2 Comparison of prophylactic and curative sprays with
thifluzamide
Thus the present studies reveal that Thifluzamide 24%
SC @ 90 and 110g a i/ha were found highly effective in
controlling paddy sheath blight. The fungicide applied both
as preventative and curative measure performed
significantly superior over standards (Hexaconazole and
Validamycin). Devi et al. (1987), found the best curative
and protective effect of Validamycin against sheath blight of
rice whereas, maximum grain yield was obtained from
Profenophos treated plots. While comparing with standards
Thifluzamide was superior as prophylactic spray, but with
the same chemical as curative performed slightly better over
prophylactic spray (Fig 2). The difference in the efficacy as
prophylactic and curative is very less; Thifluzamide can be
applied as curative treatment against sheath blight when the
third to fourth leaf from the top shows symptoms and extent
of damage caused on a particular variety. In addition to its
efficacy and increasing yield at higher dosage, Thifluzamide
was found to have phytotonic effect with appreciable green
with luxuriant growth of rice plants. The best time to apply
chemicals is at the jointing stage, during which time the
percentage tiller infected was highly correlated with sheath
blight at wax ripeness stage: percentage yield loss depended
on disease index at wax ripeness (CPC 2005). Prophylactic
application targeted at this stage proved as the right stage of
application against initial infection by Rhizoctonia solani.
Singh and Singh (2009) observed that the application of
Validamycin at tillering stage of rice crop seems to have
positive effect in enhancing the efficacy. Fungicides having
least residues in food, feed and soil are being encouraged in
present day agriculture. Thifluzamide at higher doses (90
and 180g a i/ha) did not show any residues in grains, straw
and soil and proposed PHI being 28 days which is found to
be less than acceptable limit. Yi and Lu (2006) found that
probenazole residues in soil, brown rice, and water were
undetectable at levels of recommended and doubled dosage
with an interval of 63 days. This study signifies that
fungicide Thifluzamide at 90 and 180g a i/ha recommended
for management of paddy sheath blight, which could be
considered as safe to paddy plants, human beings and soil
environment. These would contribute to provide the
scientific basis of using this fungicide.
Thifluzamide 24 % SC a new group fungicide was
found effective both as preventive and curative activity
without any symptoms of phytotoxicity, reducing the disease
severity and increasing the yield. The cost of managing the
disease by two applications is covered by the extra yield
achieved due to suppression of the disease, where it was
found significantly superior to the standards. Residues of
Thifluzamide and its metabolite in grain, straw and soil were
found below the quantifiable limit at the test doses.
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