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Chapter V
DISCUSSION
The results obtained during the present investigation entitled,
“Integrated Pest Management in Okra, Abelmoschus esculentus (L.) Moench”
are discussed hereunder:
5.1 Insect-pests associated with okra crop
For evolving an effective pest management strategy, it is
imperative to know the insect-pest complex attacking a crop in a particular
agro-climatic zone. Surveillance studies conducted on okra at Palampur
revealed 18 different pests’ species belonging to 6 orders and 12 families
associated with A. esculentus (var. Pusa Sawani) from June to September
(Table 4.1). At Kachhiari (Kangra), 19 different pests’ species belonging to 6
orders and 12 families were associated with okra crop from May to
September (Table 4.2). At both the locations, Nodostoma spp. and Popillia
spp. were identified as new insects of okra from the state. Nodostoma spp.
were found to attack both foliage and flowers whereas Popillia spp. attacked
flowers only although both these insects were rated as minor pests.
Earlier Butani and Verma (1976) had reported as many as 30 insect
and non-insect pests attacking okra crop. Dhamdhere et al. (1984) have
listed 13 pests attacking okra at various stages of crop growth at Gwalior in
Madhya Pradesh. Eight species of insects were reported to feed on okra at
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Raipur (Chhattisgarh) by Dubey et al. (1999). Our results are in close
consonance with Nath (1992) who reported 21 species of insects-pests
associated with okra crop at Solan, Himachal Pradesh and Singh and Joshi
(2004) who observed 15 pests associated with okra crop in Paonta valley of
Himachal Pradesh.
During the present investigation, the severity of pests was noticed
from June to September at both the locations. A number of workers have
also observed that the pests of okra are more serious from June to August
i.e. during warm and rainy season (Kashyap and Verma, 1982; Mahmood et
al., 1988; Kandoria et al., 1989).
The present research revealed that out of 18 pest species recorded
on okra at Palampur, 4 were observed to cause major damage to crop.
These included jassid, A. biguttula biguttula, aphid, A. gossypii, blister
beetle, M. pustulata and leafroller, S. derogata. At Kachhiari, in addition to
these pests, shoot and fruit borer, E. vittella was also observed as the major
pest of okra.
A. biguttula biguttula and E. vittella have already been recognized
as most serious pests of okra crop in different parts of country by many
researchers (Mote, 1977; Radke and Undirwade, 1981; Dhamdhere et al.,
1984; Gajbhiye et al., 1985; Chaudhary and Dadheech, 1989; Jamwal and
Kandoria, 1990; Kadam and Khaire, 1995; Bhagat and Bhat, 1999; Dubey et
al., 1999; Gogoi and Dutta, 2000; Mandal et al., 2006c, Gupta et al., 2007;
Singh, 2007; Singh et al., 2007).
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The current findings also find favour with Nath (1992) who
reported A. biguttula biguttula as major pest of okra from Solan valley of
Himachal Pradesh. Likewise, Bhatia and Gupta (2003) reported A. biguttula
biguttula as most serious pest of okra in Himachal Pradesh. The severity of
this pest on okra has also been described by Singh and Joshi (2004) from
Paonta valley of Himachal Pradesh and Kumar and Pathania (2006) from Una
in Himachal Pradesh.
A. gossypii has previously been reported to cause considerable
damage to okra crop in different parts of the country (Chaudhary and
Dadheech, 1989; Kandoria et al., 1989; Jamwal and Kandoria, 1990;
Devasthali and Saran, 1997; Patel et al., 1997a).
M. pustulata found as the major pest in current study has been
earlier observed feeding on floral parts of okra plant by Sharma et al.
(1964), Dhamdhere et al. (1984) and Sangha and Mavi (1995). The serious
infestation of blister beetle, M. phalerata on okra at Manipur has been
mentioned by Barwal and Rao (1988). Under mid hill conditions of Himachal
Pradesh, blister beetle has been reportedly observed attacking okra flowers
and thus lowering the yield (Kakar and Dogra, 1988; Anonymous, 2005b).
Even Nath (1992) observed Mylabris spp. to be causing principal damage to
okra in Solan valley of Himachal Pradesh. Sharma (2004) reported 4 species
of Mylabris associated with okra crop.
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However, Singh and Joshi (2004) mentioned aphids and blister
beetle as minor pests of okra. This can be attributed to the difference in
weather conditions which leads to variation in intensity of damage caused by
a pest from one region to another. In addition to these pests, S. derogata
too caused substantial damage to okra crop in the current investigation. The
damage by S. derogata to okra crop has formerly been cited by Dhamdhere
et al. (1984), Ghosh et al. (1999) and Singh and Joshi (2004).
A deep insight into the insect-pests associated with okra crop at
two locations revealed that in summer, less incidence of different pests was
observed (except E. vittella) as compared to the rainy months possibly
because of high temperature and low humidity prevalent in summers. This
view is supported by Sardana and Verma (1986) who based on their study
on cowpea concluded that in summer, low humidity and high temperature
are important factors in keeping insect population density at a low level in
comparison to rainy season.
In the current study, E. vittella was observed causing substantial
damage to okra fruits only at Kachhiari while at Palampur, it was present in
low numbers. This could be ascribed to the fact that at Kachhiari, the crop
was sown in the month of April and harvested in August/ September, thus
experiencing both summer and rainy seasons, whereas, at Palampur, the
crop was sown in end of May or beginning of June, which resulted in main
fruit bearing period during rainy season. Due to heavy rainfall in July-August
185
at Palampur, the pest was unable to multiply and thus remained in lower
proportion. Further, higher temperature and lower humidity prevailing at
Kachhiari during initial stages of fruit setting were found quite suitable for
the development of the pest.
Madav and Dumbre (1985) detected no incidence of shoot and fruit
borer on okra throughout the kharif season in Maharashtra. Even Singh and
Brar (1994) reported from Ludhiana (Punjab) that the late sown crop of okra
(in July) revealed quite low infestation of E. vittella. The adverse effect of
high relative humidity (> 60%) and rainfall (> 20 mm/week) on E. vittella in
okra has been previously quoted (Kadam and Khaire, 1995).
5.2 Seasonal incidence/population build-up of major insect-pests on okra crop
The period of commencement of pest activity is known to fluctuate
depending on the prevalence of environmental conditions and availability of
suitable hosts.
5.2.1 Cotton jassid, A. biguttula biguttula
Appearance of jassids on okra was first noticed in the fields at
Palampur during 1st week of July during the two seasons whereas, at
Kachhiari, the pest was first seen in 4 th week of May during 2005 and 3rd
week of May during 2006 (Tables 4.3 – 4.4). The early appearance of the
pest at Kachhiari was probably due to early sowing of the crop in the month
of April as compared to Palampur (May/June).
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The population, after attaining an increasing trend through the
months of July and August with a population range of 2.25-46.20 jassids per
3 leaves at Palampur and 0.60-51.02 jassids per 3 leaves at Kachhiari
varying through the two seasons declined towards the end of crop growth
period but did not cease completely. These results are in agreement with
Patel et al. (1997a) who also observed that the jassid population on okra
amplified during the monsoons. The present findings are broadly in
corroboration with the research results of few workers (Mahmood et al.,
1990; Anonymous, 2005a) who observed the emergence of jassids on okra
in June-July, which remained active till the end of crop growth.
The existing results are also supported by those of Patel et al.
(1997a) who observed that the period of incidence of A. biguttula biguttula
lasted from July to September on okra under Gujarat conditions. Earlier also,
increased population of jassids on okra has been reported during the months
of July to September by Jayaraj and Basheer (1964), Uthamasamy et al.
(1973) and Uthamasamy (1988). Higher population of okra jassids in rainy
season as compared to summer season witnessed during the present study
get support from reports by Mohan et al. (1983) and Mishra and Senapati
(2003).
The peak of jassid population was observed in 3 rd to 4th week of
August at Palampur (45.86 and 46.20/3 leaves) and 4 th week of July to 1st
week of August at Kachhiari (39.21 and 51.02/3 leaves) during the two
seasons. Similarly, highest population of 18.00 jassids per okra leaf (Bhat,
187
1999) and 10.34 jassids per okra leaf (Anonymous, 2005a) has been
observed in the last week of August at Jammu and Varanasi, respectively,
thus justifying the present findings. On the other hand, Krishnananda (1973)
and Balasubramaniam et al. (1977) reported a rise in the population of A.
biguttula biguttula during November-December. The difference in peak
activity period could be attributed to variation in weather conditions
prevailing over a particular place, the cropping season, time of sowing and
variety of crop grown.
The peak of jassid population was observed when the
meteorological conditions were 27.4-29.7oC (maximum temperature), 18.8-
25.3oC (minimum temperature), 75-80 per cent (relative humidity), 5.9-7.5
hours (bright sunshine hours) and 64.4-115.0 mm (total rainfall). The
meteorological range prevalent during the peak activity in the present
investigation has been reported to be favourable for the development of this
pest by earlier workers also.
Murugesan (1985) and Gupta et al. (1997) found peak population
of jassid when the minimum and maximum temperature ranged between
24.8 to 32.6oC. Further, Gupta et al. (1997) found relative humidity of 78
per cent conducive for multiplication of jassids which is in close harmony to
that found in the present study. Singh and Sekhon (1998) also substantiate
the present findings by reporting mean temperature of 30oC coupled with
less than 8.6 hours of bright sunshine (preferably 5 hours/day) favourable
for increase in jassid numbers.
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5.2.2 Cotton aphid, A. gossypii
At Palampur, the aphid activity commenced in 1st week of July
whereas at Kachhiari, it was evident in last week of June during both the
seasons. The population witnessed an increasing trend throughout the
months of July, August and September at Palampur and Kachhiari,
diminished a bit towards the end of crop maturity but was still present in
ample numbers at the time of final harvest (Tables 4.6-4.7). In the present
study, negligible incidence of aphids was observed in the month of June at
Kachhiari which augmented on the onset of monsoon. Kandoria et al. (1989)
also reported reduced population of aphids on okra during the summer
months (May-June) because of high temperature prevalent during that
period.
The existing results fairly match with those of Jamwal and
Kandoria (1990) who noticed the activity of A. gossypii on okra from 4th
week of July to 3rd week of October. In the present study, aphid population
sustained all throughout the cropping seasons and was present in substantial
numbers even towards the end of crop growth. Similar observations were
made by Ghosh et al. (1999) while studying seasonal incidence of aphids on
okra at Pundibari (West Bengal). On the contrary, aphids were most active
on okra during September-October in Punjab (Kandoria et al., 1989). The
variation in seasonal incidence is due to prevailing weather conditions which
differ from one region to other.
189
At Palampur, peak aphid population was observed in 2nd to 3rd
week of August (85.27 and 94.65/3 leaves) whereas, at Kachhiari, it was
maximum during 2nd to 4th week of July (54.75 and 68.25/3 leaves). These
results broadly match with Ghosh et al. (1999) who viewed initiation of A.
gossypii activity on okra in mid June which reached in peak in the last week
of July and also with Al Eryan et al. (2001) who noticed appearance of
aphids on okra in the month of July which reached its peak in late August.
During the present investigation, peak population of aphid (A.
gossypii) was observed when mean maximum temperature ranged between
25.1-28.3oC, mean minimum temperature ranged between 19.2-25.4oC,
mean relative humidity ranged between 85-89 per cent, mean bright
sunshine ranged between 2.5-3.1 hours with total rainfall of 100.4-212.5
mm.
The present results regarding the favourable meteorological range
for A. gossypii is in harmony with the findings of Murugesan (1985) who
reported humid weather conditions highly favourable for cotton aphid. These
findings also find favour with Dhamdhere et al. (1995) who observed that
moderate temperature (27.3-28.2oC) and high humidity (73 %) favoured
build-up of A. gossypii on brinjal at Gwalior in Madhya Pradesh. Further,
Gupta et al. (1997) based on their two year study at Harda in Madhya
Pradesh found moderate range of minimum and maximum temperature
(24.8-30.1oC), high humidity (87-89 %) and drizzling rainy days quite
conducive for rapid build-up of aphid population on cotton, thus backing up
the current results.
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Critical appraisal of jassid and aphid incidence in relation to
weather parameters on okra in the present research indicated that the jassid
multiplication was favoured by higher maximum temperature (27.4-29.7oC)
and lower relative humidity (75-80%) as compared to that of aphid
population which was favoured by comparatively lower maximum
temperature (25.1-28.3oC) and higher relative humidity (85-89%). Similar
observations on the incidence of jassids and aphids were made by Gupta et
al. (1997) on cotton crop in Madhya Pradesh. They reported that higher
maximum temperature (32.6oC) and lower relative humidity (78%) were
conducive for the multiplication of A. biguttula biguttula whereas, lower
maximum temperature (26.1-30.1oC) and higher relative humidity (87%)
were found favourable for rapid build up of A. gossypii population.
Prevalence of higher humidity at Palampur as compared to
Kachhiari also explains the presence of higher aphid population at Palampur
during the current investigation. Although high rainfall was received during
the study period even then the aphids were present in considerable
numbers. This could be because of the fact that aphids have developed
several modes of reproduction such as viviparity, paedogenesis,
parthenogenesis etc. for their survival as has been mentioned by Dhaliwal
(2006).
5.2.3 Shoot and fruit borer, E. vittella
The appearance of E. vittella on okra fields was first noticed in 3rd
to 4th week of May at Kachhiari during the two seasons. A low incidence on
shoots varying between 0.82-2.24 per cent was observed initially for two
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weeks. As soon as the fruit setting started, the pest started infesting fruits
and by 1st week of June and thereafter, no damage on shoots was observed
(Table 4.9). The pest continued infesting fruits till 2nd week of July to 1st
week of August varying between 1.23-35.85 per cent and the larval
population varied between 0.37 to 2.35 per fruit during the two seasons.
Ambekar et al. (2000a) also observed negligible incidence of E.
vittella on okra shoots at Pune in Maharashtra. Analogously, Mandal et al.
(2006b) reported lower damage of shoot and fruit borer on okra shoots
varying between 0.3 to 3.46 per cent at Samastipur (Bihar). They also
observed that after fruit setting, there was no damage on shoots and the
pest shifted its activity exclusively on fruits, which corroborates the present
results.
Varying levels of fruit damage by E. vittella on okra crop ranging
between 32.1-100.0 per cent have been reported by various workers (Radke
and Undirwade, 1981; Dhawan and Sidhu, 1984; Madav and Dumbre, 1985;
Chaudhary and Dadheech, 1989; Kadam and Khaire, 1995; Gupta et al.,
1998; Mathur et al., 1998; Mandal et al., 2006b) depending on prevailing
agro-climatic conditions in their respective areas of study.
Peak fruit infestation (29.64 and 35.85%) during the current study
was noticed during 3rd to 4th week of June which in the following weeks
declined and ceased completely by 3rd week of July to 2nd week of August
because of heavy rainfall received during the later period. Almost similar
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pattern of fruit infestation on okra was observed by Mote (1977) at Rahuri in
Maharashtra, according to whom, E. vittella infestation started as soon as
the fruits set (6 weeks after germination), attained a maximum 3-4 weeks
later during summer after which it declined.
The peak activity of the pest noticed during the month of June is in
accordance with Shukla et al. (1997) from Jabalpur (Madhya Pradesh) who
reported peak fruit damage by E. vittella in 1st fortnight of June. The peak
period of activity of E. vittella in India has been known to vary from region
to region i.e. late October in Punjab (Dhawan and Sidhu, 1984), November-
December in Maharashtra (Kadam and Khaire, 1995), 4 th week of July in
Bihar (Gupta et al., 1998), 2nd fortnight of August in West Bengal (Ghosh et
al., 1999), 4th week of September in Gujarat (Zala et al., 1999) and 4th week
of October in Uttar Pradesh (Anonymous, 2005a). The variation in peak
activity may be ascribed to difference in meteorological conditions prevailing
over a particular place, cropping season, time of sowing and variety of crop
grown.
More severity of E. vittella on okra crop sown in the summer
months as compared to one sown in rainy season was noticed by Mohan et
al. (1983) and Kumar and Urs (1988). Related observations were also made
by Dhawan and Sidhu (1984) who reported from Punjab that maximum
damage to okra fruits by E. vittella was evident in spring crop and that
heavy rainfall adversely affected population build-up of this pest. Lower
193
incidence of E. vittella because of heavy rainfall has also been documented
by Kadam and Khaire (1995) at Ahmednagar, Maharashtra. They observed
high damage by E. vittella during summer months and low damage during
rainy months.
The lower damage recorded during the rainy season could be
because of dislodgement of eggs and neonate larvae of shoot and fruit borer
by the rains as well as the prevalence of high humidity. According to Kadam
and Khaire (1995), the adverse effect of high relative humidity (> 60%) and
rainfall (>20 mm/week) could form a component of eco-friendly
management of Earias species. Further, they reported that infestation could
be reduced to a greater extent by growing okras during the rainy season.
The mean meteorological conditions present during the peak pest
activity were maximum temperature of 34.6-35.3oC, minimum temperature
of 21.9-26.9oC, relative humidity of 36-47 per cent and 12.1-31.2 mm of
total rainfall. These observations are substantiated by Radke and Undirwade
(1981) who found peak infestation on okra fruits (100%) by Earias spp.
when average weekly maximum temperature was 30.8oC, minimum
temperature was 21.1oC and relative humidity was 49 per cent. In the past,
a number of workers have reported temperature of about 35oC to be
congenial for the development of this pest which supports the present
findings (Ahmad and Ullah, 1941; Pradhan and Menon, 1945; Kashyap and
Verma, 1982).
194
5.2.4 Blister beetle, Mylabris spp.
Seasonal incidence studies on okra revealed that Mylabris beetles
emerged in okra fields in 4th week of July to 1st week of August at Palampur
and 1st to 3rd week of July at Kachhiari (Tables 4.11-4.12). These results are
in corroboration with Sharma et al. (1964) who reported that the blister
beetles appeared in July in Himachal Pradesh on various crops including
okra. Similar observations were made by Sangha and Mavi (1995) from
Ludhiana (Punjab) who reported that M. pustulata appeared in 2nd fortnight
of July on okra.
The peak activity of the pest was observed in 3 rd week of August to
1st week of September at Palampur with maximum population of 24.5-29.6
beetles per 10 plants and maximum flower damage of 26.90-31.15 per cent.
At Kachhiari, peak activity was observed in 2nd to 3rd week of August with
maximum beetle population varying between 31.8-35.6 per 10 plants and
flower damage varying from 32.69-38.52 per cent. A declining trend was
then set in and low beetle incidence was observed in 2nd to 4th week of
September at Palampur and 4th week of August to 1st week of September at
Kachhiari.
During the present study, maximum beetle population and flower
damage were viewed when the mean meteorological conditions of 27.7-
29.1oC (maximum temperature), 20.2-25.8oC (minimum temperature), 75-79
per cent (relative humidity), 7.1-7.9 hours (bright sunshine) and 37.8-80.5
195
mm (total rainfall) were prevalent. These findings are supported by reports
of Sharma et al. (1964) from Himachal Pradesh and Sangha and Mavi (1995)
from Punjab who observed peak activity of blister beetle on okra during the
month of August. The present results also find favour with Dutta and Singh
(1989) who reported that M. phalerata population peaked in August at the
time of flowering in pigeon-pea in Uttar Pradesh.
The favourable range of meteorological parameters for blister
beetle multiplication observed during the present study is validated by
Sardana and Verma (1986). They found that blister beetle, M. pustulata
showed its peak on cowpea between last week of August to 1st week of
September at Delhi when maximum temperature varied between 25-32oC
and relative humidity varied between 60-92 per cent with total rainfall
ranging from 20 to 90 mm. The existing findings are also in line with
Bhardwaj (1996) who reported that on black gram, peak blister beetle
population was noticed in 4th week of July to 1st week of September in
Himachal Pradesh when mean temperature and relative humidity were 23.3-
25.0oC and 72-85 per cent, respectively, with total rainfall of 16.2 mm-273.4
mm.
5.2.5 Cotton leafroller, S. derogata
The present studies revealed that the leafroller activity was first
evidenced on okra plants during 2nd to 4th week of July at Palampur while at
Kachhiari, it was first observed in last week of June to 1st week of July
196
(Table 4.14 - 4.15). The highest incidence of S. derogata on okra was
observed in 1st to 3rd week of August at Palampur with maximum larval
population of 34.7-38.1 per 10 plants as well as maximum rolled leaf
infestation of 26.97-29.21 per cent. At Kachhiari, maximum population of
33.8-36.3 larvae per 10 plants and maximum rolled leaf infestation of 25.70-
27.16 per cent were observed during last week of July during both the
seasons. During the peak activity, the meteorological conditions prevalent at
the two locations were mean maximum temperature in the range of 25.8-
28.4oC, mean minimum temperature in the range of 20.1-25.4oC, mean
relative humidity in the range of 80-89 per cent, mean bright sunshine in the
range of 2.3-3.1 hours and total rainfall of 100.4-211.2 mm.
Literature regarding the seasonal incidence of S. derogata on okra
is meagre. However, Lal and Singh (1951) reported low temperature and
high humidity coupled with rainy days favourable for the development of leaf
roller which is in accordance with the present results. These findings are also
in consonance with Ghosh et al. (1999) who observed that population of
okra leafroller initiated in 1st week of July at Pundibari (West Bengal) and
higher population (0.80 larva/plant) was maintained till August which
decreased gradually thereafter. They noticed maximum population of the
pest at mean maximum temperature of 29.3oC, mean minimum temperature
of 24.0oC and mean relative humidity of 90-97 per cent, thereby broadly
validating the present findings.
197
5.3 Correlation of abiotic factors with population build- up of major insect-pests on okra
5.3.1. Cotton jassid, A. biguttula biguttula
At Palampur during 2005, rainfall exhibited a significant negative
outcome while bright sunshine hours showed a significant positive
relationship with population count of the pest. During 2006, none of the
weather factors showed a significant correlation with pest population (Table
4.5). Interestingly, at Kachhiari, maximum temperature negatively but non-
significantly influenced pest activity while relative humidity had a significant
positive impact on jassid population during both the years of study. Besides,
minimum temperature influenced pest activity significantly and positively at
Kachhiari during 2006 (Table 4.5).
The present results are in line with those of Reddy et al. (1983),
Dhuri et al. (1984) and Faleiro and Singh (1985) who observed positive
correlation of minimum temperature and relative humidity with jassid
population on a variety of crops. The positive correlation of A. biguttula
biguttula with relative humidity is in conformity with Jayaraj and Basheer
(1964) who observed humid season quite conducive for population build-up
of this pest.
The positive correlation of the jassid density with minimum
temperature is in accordance with Mahmood et al. (1990). These workers,
however, contrary to the present results, observed no significant
contribution of relative humidity and rainfall in influencing the pest numbers.
198
This is because of the difference in climatic conditions which vary from one
place to another. The significant negative correlation of jassid count with
rainfall at Palampur (2005) could be attributed to comparatively higher and
almost incessant rainfall received during 2005 as compared to 2006 which
would have led to the splashing of mud on to the underside of leaves,
resulting in mortality of jassids. Similar reports are available from Sudan
where good suppression of jassid population on cotton was brought about by
heavy rainfall (Hanna, 1970).
The significant negative correlation of jassid count with maximum
temperature and positive correlation with bright sunshine has earlier been
illustrated by Patel et al. (1997a) on okra. Likewise, positive correlation of
population count of jassids with average relative humidity has been
previously mentioned by Sharma and Sharma (1997). Bhat (1999) while
correlating A. biguttula biguttula population and abiotic factors at Jammu on
okra revealed that the population was negatively correlated with rainfall
while significantly and positively correlated with bright sunshine hours which
is in complete agreement with the present results.
The wide variation in correlation coefficients obtained between
abiotic factors and jassid population at Palampur and Kachhiari could be
ascribed to the fact that at Kachhiari, the crop passed through the hot
summer months as well as rainy season whereas, at Palampur, the crop
underwent through the rainy season only, thus the pest experienced wide
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variation in maximum and minimum temperature, relative humidity and
rainfall at the two locations but multiplied only when the favourable range of
meteorological conditions were available. Dhaliwal and Arora (2003) also
mentioned that the degree of influence of environmental factors determines
the magnitude of increase or decrease in numbers of a pest population and
that every insect species multiplies only when the favourable range of
meteorological conditions are approached.
5.3.2 Cotton aphid, A. gossypii
The population of aphids on okra illustrated a positive significant
correlation with relative humidity at both the locations during both the years
(Table 4.8). In addition, pest numbers were significantly and negatively
correlated with maximum temperature at Palampur during 2005 and at
Kachhiari during both the seasons. Conversely, minimum temperature
correlated positively and significantly with aphid density at Kachhiari during
2006.
The present results are in concordance with Feleiro et al. (1990)
who revealed that on cowpea, population of A. gossypii was negatively
correlated with maximum temperature and sunshine hours and positively
correlated with minimum temperature and relative humidity in Delhi.
Likewise Gupta et al. (1997) observed significant positive relationship
between aphid density and relative humidity and significant negative
relationship with maximum temperature on cotton in Madhya Pradesh. These
results are also in tune with Ghosh et al. (1999) who reported negative and
200
non-significant correlation of aphid count with maximum temperature and
non significant and positive correlation with relative humidity on okra in
West Bengal.
5.3.3 Shoot and fruit borer, E. vittella
At Kachhiari, maximum temperature exhibited a significant positive
correlation with fruit infestation as well as larval population during both the
seasons while relative humidity illustrated a significant negative relationship
with fruit infestation during 2005. Besides, rainfall had a significant negative
correlation with larval population during 2005 (Table 4.10). Radke and
Undirwade (1981) have also observed higher incidence of E. vittella on okra
with increase in temperature. The adverse effect of rainfall on population
build-up of E. vittella has been observed by Dhawan and Sidhu (1984) at
Ludhiana, Punjab.
The present correlation analysis is also supported by Kumar and
Urs (1988) from Bangalore and Zala et al. (1999) from Gujarat who noticed
that temperature had a positive and significant association with incidence of
E. vittella while relative humidity was negatively related with pest incidence.
Parallel results were obtained by Kadam and Khaire (1995) from Rahuri,
Maharashtra who observed a significant and negative correlation between
relative humidity, rainfall and E. vittella infestation on okra. Likewise, Bhat
(1999) viewed negative correlation of rainfall and fruit infestation by E.
vittella on okra in Jammu which is in close agreement with the present
findings.
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However, on the contrasting side, a significant negative correlation
between okra fruit infestation by E. vittella and maximum temperature while
significant positive relationship with total rainfall was analyzed by Gupta et
al. (1998) and Mandal et al. (2006b) in Bihar. This difference could be
ascribed to the variability in weather conditions from one place to another.
5.3.4 Blister beetle, Mylabris spp.
During 2005, at Palampur as well as Kachhiari, none of the
weather factors influenced beetle population as well as flower damage
significantly (Table 4.13). Nonetheless, during 2006 at Palampur, there was
a significant positive correlation between beetle population, flower damage
and maximum temperature. In addition, relative humidity had a significant
negative bearing while bright sunshine hours had a significant positive
bearing on flower damage at Palampur in 2006. Further, minimum
temperature exerted a significant negative impact on flower damage by
Mylabris spp. at Kachhiari during 2006.
There are no reports available on okra to validate the present
results. However, some reports are available in the literature pertaining to
the effect of weather factors on blister beetle population in pigeon-pea.
Sekhar (1991) reported that daily temperature and sunshine hours had a
significant positive effect while relative humidity showed a non-significant
negative correlation with blister beetle activity, which corroborates present
results. Identical reports are available from New Delhi in which, positive
correlation of M. pustulata population with maximum temperature and bright
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sunshine hours have been illustrated (Reddy et al., 2001). Even Sandal
(2007) reported a significant and positive correlation of Mylabris population
with maximum temperature on pigeon-pea at Palampur in Himachal Pradesh,
thus supporting present results.
5.3.5 Cotton leafroller, S. derogata
The present studies revealed that S. derogata larval population
positively and significantly correlated with relative humidity at Kachhiari
during both the crop seasons while at Palampur during 2006 only (Table
4.16). Contrastingly, bright sunshine hours exercised negative and
significant effect on larval population as well as per cent rolled leaf
infestation at Palampur during 2006. In addition at Kachhiari during 2006,
maximum temperature displayed a significant negative association with
larval population.
Low temperature and high humidity have earlier been found
favourable for the development of S. derogata on okra by Lal and Singh
(1951). The significant negative influence of bright sunshine hours on leaf
roller activity can be substantiated by the work of Lal and Singh (1951) and
Butani and Verma (1976) who have mentioned cloudy weather and rainy
days congenial for the activity of this pest. Ghosh et al. (1999) also support
the current findings by obtaining negative and non-significant correlation of
leafroller larval population with maximum temperature and positive and
significant correlation with minimum temperature and relative humidity on
okra at Pundibari (West Bengal).
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5.4 Screening of okra varieties/hybrids for resistance against major insect-pests Development and cultivation of resistant varieties to pests provides
a suitable and desirable means of pest management. The success of such
programme depends upon the extent of variability in the germplasm.
Further, in crops such as okra, frequent pickings, high operational cost and
residual effect of insecticides are the limiting factors for the management of
insect-pests through chemicals. Therefore, the most effective and
economical management of okra pests is the use of resistant varieties but a
variety resistant to a pest in one region may become susceptible in other
region. Hence, ten okra varieties/hybrids (including 3 recommended
commercial varieties for Himachal Pradesh) were evaluated for their relative
susceptibility against major insect-pests at two locations viz. Palampur and
Kachhiari.
5.4.1 Cotton jassid, A. biguttula biguttula
The mean jassid population (nymphs + adults) varied from 8.52 to
36.12 per 3 leaves on different varieties during the two seasons at two
locations (Table 4.17-4.19). Variety Tulsi (8.52-10.71 jassids/3 leaves) and
Varsha Uphar (8.83-11.93 jassids/3 leaves) showed lower population of the
pest at Palampur. At Kachhiari also, Tulsi revealed lowest jassid population
(11.33-11.61/3 leaves) while Varsha Uphar (14.74-15.25/3 leaves) was rated
as one having moderate population. Other varieties which recorded
moderate pest numbers at Palampur were Arka Anamika, Parbhani Kranti
and Panchaali while at Kachhiari, the same varieties were categorized in the
group of high population.
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The variation in susceptibility among varieties could be due to
certain inherited characters as well as due to variable environmental
conditions from region to region and year to year. These findings get
support from those of Kashyap and Verma (1986) who reported similar
reasons for difference in susceptibility among genotypes. The wide variation
with respect to rating of varieties at the two locations could be allotted to
the wide variation in overall pest pressure which was lower at Palampur as
compared to Kachhiari.
Variation in morphological characters as well as biochemical
components must have contributed to differential response of varieties
(Taylo and Bernardo, 1996; Dhaliwal and Arora, 2003) to jassids.
Uthamasamy et al. (1973) obtained a positive correlation of jassid incidence
with plant height and stem thickness in okra. It is known that the varieties
viz. Pusa Makhmali, P-8, Harbhajan and Parbhani Kranti are tall (Singh,
2007) and accordingly must have harboured more jassid population in the
current study. Teli and Dalaya (1981b) reported that Pusa Sawani showed
lower hair density (3.80/25mm2) on leaf lamina as compared to other
varieties and was more preferred for oviposition by jassids. It has also been
observed that okra varieties having more and longer hairs on the mid-rib and
leaf lamina are resistant to jassid (Uthamasamy, 1985; Singh, 1988; Singh
and Agarwal, 1988; Lal et al., 1997).
205
Soft stem hair present in Parbhani Kranti, Pusa Sawani and P-8 and
lower hair density on mid veins of Pusa Sawani leaves (Mahal et al., 1993b;
Sharma and Arora 1993; Gill et al., 1997; Hooda et al., 1997; Dhankhar and
Mishra, 2001; Thakur et al., 2003) can partly explain higher jassid
population harboured by these varieties.
Even though Pusa Makhmali has hairy stem and leaves (Sharma
and Arora, 1993; Dhankhar and Mishra, 2001), it was reported as susceptible
variety in the present investigation. This could be because of the fact that
for an okra variety to be resistant to jassids, the complete complement of
hair characters viz. long, dense and erect are required as has been
mentioned by Singh and Taneja (1989) plus the composition of right amount
of different biochemicals, which could be lacking in this variety, thus proving
susceptible. Teli and Dalaya (1981b) too observed White Velvet variety of
okra as susceptible to jassid even though it had highest hair density
(9.30/25mm2) among the 6 varieties tested.
The existing findings are also supported by those of Bhat (1999)
who observed Varsha Uphar and Arka Anamika to be less preferred by
jassids (6-10/okra leaf) as compared to Shagun and Parbhani Kranti (15-
20/leaf). He has ascribed more trichome length (0.57-0.80 mm) and
trichome density (13.63-21.36/cm2) in less preferred varieties (Varsha
Uphar, Arka Anamika) responsible for providing resistance against jassids by
impeding feeding, oviposition and adult emergence.
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Among the different biochemical components, varieties of okra
having higher tannins, phenols, epicuticular waxes, silica and potassium and
lower moisture, proteins and total sugars in leaves have been reported to be
resistant to jassid (Singh, 1988; Singh and Agarwal, 1988, Singh and Taneja,
1989; Kaur et al., 1996). Comparatively lower proteins (12.81-13.21%),
moisture (64.15-69.22%) and sugar content present in leaves of Arka
Anamika and Varsha Uphar and more proteins (16.40-18.52%), moisture
(78.00-89.20%) and sugars in leaves of Parbhani Kranti, P-8, Pusa Sawani
and Shagun (Chavan et al., 1991; Reddy et al., 1997; Bhat, 1999) are
accountable for the relative resistance and susceptibility of these varieties.
The susceptibility of Pusa Makhmali and Harbhajan varieties to
okra jassids has been previously quoted in the literature (Sandhu et al.,
1974; Gill et al., 1997). The relatively low susceptibility of variety Varsha
Uphar to jassid noticed during the present investigation was also reported by
Dhankhar and Mishra (2001). Likewise, moderate susceptibility of Parbhani
Kranti (Bhat, 1999; Dubey et al., 1999) and higher susceptibility of Shagun
to A. biguttula biguttula (Bhat, 1999) have been earlier illustrated. High level
of susceptibility to jassid reported in Pusa Sawani is in consonance with the
work of Sandhu et al. (1974), Uthamasamy and Subramaniam (1980), Mahal
et al. (1993b), Gill et al., (1997), Hooda et al., (1997), Sharma and Sharma,
(1998) and Kumar and Singh (2002) who obtained similar results from their
respective areas of study.
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5.4.2 Cotton aphid, A. gossypii
The mean seasonal population of aphids on okra ranged from
18.96-70.54 individuals per 3 leaves on different varieties at the two
locations (Table 4.20-4.22). Among the different varieties, Tulsi (31.29-
39.44/3 leaves) and Varsha Uphar (35.81-43.94/3 leaves) showed moderate
level of aphid infestation on okra leaves at Palampur during the two seasons.
At Kachhiari, lower infestation by the pest was noticed on varieties Tulsi
(18.96-20.85/3 leaves), Varsha Uphar (21.15-24.61/3 leaves), Arka Anamika
(26.15-29.72/3 leaves) and Parbhani Kranti (25.93-30.08/3 leaves) while at
Palampur, the latter two varieties fall in the mean rating of high population.
This fluctuating trend, varying through seasons and locations is
ascribed to inherited characters of varieties as well as environmental
conditions. Ghosh et al. (1999) reported moderate level of infestation of A.
gossypii on Parbhani Kranti (14.64/leaf) and Arka Anamika (21.58/leaf)
which corroborate present results.
Certain morphological characters might have been responsible for
differential aphid attack. Roy (1990) mentioned thick okra leaves to be a
criterion for aphid resistance. Khan et al. (2000) reported that genotypes of
ashgourd having higher trichome density were least infested by A. gossypii
and thus provide a first line of defence in reducing aphid infestation. Lower
trichome density has been reported in leaves of Parbhani Kranti, Shagun and
Pusa Sawani (Teli and Dalaya, 1981b; Mahal et al., 1993b; Bhat, 1999)
208
making these varieties more susceptible to aphids. Likewise, Varsha Uphar
and Arka Anamika exhibit higher trichome density and length (Bhat, 1999),
thus proving to be less preferable for aphids as noticed in the present
results.
According to Dhaliwal and Arora (2003), the stem tips of cotton
varieties tolerant to A. gossypii were nearly twice as stiff as those of
susceptible cultivars and they indicated difficulty for piercing proboscis into
hard stems of tolerant varieties as one of the main causes for non-
preference by aphids. Among the biochemical constituents, Du et al. (2004)
reported that high gossypol content in cotton genotypes had an antibiotic
effect on A. gossypii by reducing adult longevity and lowering fecundity.
Comparatively higher population of A. gossypii on all the okra
varieties at Palampur as compared to Kachhiari can be attributed to the
availability of more humid weather at Palampur, in comparison to Kachhiari
which was found highly conducive for aphid multiplication. The humid
weather has previously been found favourable for rapid build-up of aphid
population by Murugesan (1985) and Gupta et al. (1997).
5.4.3 Shoot and fruit borer, E. vittella
The pest was reported as major only at one location i.e. Kachhiari.
The mean per cent fruit infestation varied between 3.79 and 24.02 during
the two years on different varieties (Tables 4.23-4.24). Varieties were
grouped according to the mean rating given by Bhalla et al. (1989) for fruit
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infestation by E. vittella. Lowest fruit infestation (3.79-4.59%) was recorded
on Tulsi which was rated as resistant while a high level of fruit infestation
was recorded on Pusa Sawani (23.41-24.02%) during the two seasons which
was rated as susceptible. Other varieties viz. Varsha Uphar, Parbhani Kranti,
Arka Anamika, Panchaali and Harbhajan also revealed lower fruit damage by
E. vittella with respective mean per cent infestation of 6.65-7.41, 8.22-9.53,
11.80-11.94, 12.77-14.58 and 13.36-13.91 during the 2 seasons and were
categorized as moderately resistant.
High level of susceptibility to E. vittella reported in Pusa Sawani
variety in the present study has earlier been demonstrated by a number of
workers (Raut and Sonone, 1979; Kashyap and Verma, 1983; Madav and
Dumbre, 1985; Sharma and Dhankhar, 1989, Vyas and Patel, 1990; Vyas
and Patel, 1991). Kashyap and Verma (1983) recorded higher fruit
infestation (20%) on Pusa Makhmali variety, thus supporting the existing
findings. Sharma and Dhankhar (1989) viewed 13.42, 17.38 and 24.52 per
cent fruit infestation on P-8, Pusa Makhmali and Harbhajan, respectively,
which is in close agreement to that found (13.36- 21.71%) in the present
investigation. Similarly, Raj et al. (1993) observed 9.89 per cent fruit
infestation by E. vittella on Parbhani Kranti and 12.87 per cent on Harbhajan
at Jachh (Himachal Pradesh), which is in complete line to that noticed (8.22-
13.36%) in the current investigation.
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Earlier Bhat (1999) had rated Varsha Uphar as fairly resistant (6-
10% fruit infestation) while Shagun as highly susceptible (>20 % fruit
infestation) to E. vittella which is in tune to the present results. Moderate
level of resistance of Parbhani Kranti and Arka Anamika with respect to fruit
damage by borer in the present study is substantiated by the findings of
Ghosh et al. (1999) who revealed that Parbhani Kranti (9.05%) and Arka
Anamika (10.10%) had low fruit infestation by E. vittella.
According to Teli and Dalaya (1981a), varieties of okra having hard
skin with tough hairs were least susceptible to E. vittella attack. Certain
morphological characters such as increased hair density on leaf lamina was
related to fruit borer resistance in okra by Kumbhar et al. (1991). Sparse
pubescence present on fruits of Pusa Sawani and P-8 (Dhankhar and Mishra,
2001; Thakur et al., 2003) and spineless fruits of Harbhajan and Arka
Anamika (Sharma and Arora, 1993; Devdas et al., 1998) could be the cause
for more preference of these varieties to fruit borer. Bhat (1999) attributed
more thickness of fruit rind in Varsha Uphar (0.33-0.35mm) and higher
trichome density on fruits (23.66-29.33/cm2) and less rind thickness and
lower trichome density in Shagun responsible for imparting relative
resistance and susceptibility of these two varieties to E. vittella as has been
observed in the present study.
Certain biochemical constituents must have also served as
defensive mechanisms against E. vittella resulting in lower incidence of the
pest in less susceptible varieties. Higher sugar content (6.96-9.88%) and
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lower total fibre content (5.47-5.74%) in Pusa Sawani (Rao and Sulladmath,
1977) could be accountable for susceptibility of this variety to shoot and fruit
borer. Singh and Singh (1987) mentioned higher tannin content in fruit
pericarp of fruit borer tolerant okra genotypes than susceptible genotypes.
Likewise, lower proteins (11.95-12.52%), sugar (5.03-5.40%), moisture
content (88.16-88.23%), ascorbic acid (100-115 mg/100g dry fruit weight),
pH level (5.4-5.8) (Devdas et al., 1998; Bhat, 1999, Yadav et al., 2006) and
more fibre, tannin and potassium content in fruits of Varsha Uphar and Arka
Anamika (Bhat, 1999) must have been the parameters for comparatively
lower fruit infestation by E. vittella observed in these varieties.
The present results are however, opposite to those obtained by
Kashyap and Verma (1983) who observed low damage (< 10%) by fruit
borer on Harbhajan variety at Hisar and Raj et al. (1993) who reported less
incidence of fruit damage by E. vittella on Pusa Sawani (6.42%) at Jachh
(H.P.) as compared to Parbhani Kranti (9.81%) and Harbhajan (12.87%).
This could be allocated to the ecological differences, variation in climate and
date of sowing of crop from region to region.
5.4.4 Blister beetle, Mylabris spp.
The mean seasonal population of Mylabris beetles per 10 plants
varied between 3.80 to 24.13 and flower damage ranged between 4.45 to
24.05 per cent at the two locations on different varieties (Tables 4.25-4.27).
Least beetle count was observed on Varsha Uphar (3.80-3.93/10 plants) at
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Palampur with minimum flower damage of 4.45-5.14 per cent. At Kachhiari
also, same variety proved to be least susceptible with pest population of
4.20-4.80 beetles per 10 plants and flower damage varying from 5.04 to
5.67 per cent during the two seasons.
The highest population of beetles (14.60-24.13/10 plants) as well
as the maximum damage to flowers (17.15-24.05 per cent) were registered
by Pusa Sawani during the two years at both the locations. Other varieties
which experienced lower pest infestation were Tulsi, Arka Anamika and
Panchaali which revealed slight variations in their differential response to
pest attack at the two locations.
On all the varieties, the overall pressure of blister beetles was
lower during 2006 as compared to 2005 crop season at both the locations.
This could be explained partly on the basis of environmental conditions and
partly on the basis that during 2006, at both the locations, pulse crops such
as pigeon-pea and cowpea were grown in the adjoining fields and this pest,
being polyphagous, damaged these crops also besides attacking okra, which
reduced population of Mylabris beetles on okra.
Literature pertaining to blister beetle incidence on okra is scanty as
this pest has been reported minor in most of the earlier reports (Dhamdhere
et al., 1984; Singh and Joshi, 2004). However, according to Dent (2000),
glandless cotton varieties are more susceptible to blister beetles. Lale and
Sastawa (2000) evaluated 6 pearl-millet varieties viz. Ex-borno, Wame,
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Zongori, Gargasori, Mboderi and GB 8735 for their relative susceptibility to
Mylabris beetles in Nigeria and found significant differences among them
with respect to damage caused by the beetles as was observed in the
present investigation on okra.
5.4.5 Cotton leafroller, S. derogata
The mean larval population of leafroller varied from 7.33 to 28.13
per 10 plants on ten varieties during the two seasons at the two locations
(Tables 4.28-4.30). Variety Varsha Uphar showed lowest number of larvae at
both the locations varying between 9.80-12.60 per 10 okra plants at
Palampur and 7.33-9.73 per 10 plants at Kachhiari throughout the two
seasons. Tulsi also registered lower larval population i.e. 12.47-15.60 per 10
plants at Palampur and 9.00-11.20 per 10 plants at Kachhiari. Likewise, the
rolled leaf infestation was minimum in Varsha Uphar i.e. 5.28-7.64 per cent
at Palampur and 4.01-4.86 per cent at Kachhiari followed by Tulsi at both
the locations. At Palampur, Pusa Makhmali recorded highest larval
population of leafroller (25.53-28.13 per 10 plants) as well as maximum
rolled leaf infestation (18.29-19.89%) followed by Pusa Sawani. Reverse was
true at Kachhiari, where maximum larval population (22.47-25.73/10 plants)
and rolled leaf infestation (15.37-17.81%) were observed on Pusa Sawani
followed by Pusa Makhmali.
At Palampur, comparatively higher incidence of the pest was
apparent on all the varieties than Kachhiari. This could be credited to the
availability of more humidity and lower temperature at Palampur during the
214
pest activity as compared to Kachhiari. Even Lal and Singh (1951) reported
that low temperature and high humidity coupled with number of rainy days
favour development of S. derogata. Other varieties which manifested low to
moderate infestation of leafroller were Arka Anamika, Parbhani Kranti and
Panchaali. Parallel results were obtained by Ghosh et al. (1999) who
reported moderate level of resistance in Arka Anamika and Parbhani Kranti
to S. derogata as compared to other varieties in West Bengal. There are no
other reports available in literature to confirm the present findings.
5.5 Marketable yield of okra varieties
Variety Tulsi registered highest yield at Palampur (67.47-72.10 q
ha-1) as well as at Kachhiari (87.72-93.03 q ha-1) and was significantly
superior to rest of the varieties. It was closely followed by Varsha Uphar
which recorded 62.56 to 84.04 q ha-1 yield at the two locations during the
two seasons. Other varieties which registered considerably higher yield at
both the locations were Arka Anamika, Panchaali, Parbhani Kranti and
Shagun. Lowest yield was however, obtained in Pusa Makhmali i.e. 29.45 to
31.49 q ha-1 at Palampur and 37.20 to 38.30 q ha-1 at Kachhiari (Table
4.31).
The variation in yield among the varieties could be accredited to
the genotypic variations, environmental difference and relative susceptibility
of different varieties to various insect-pests and diseases. Higher yield
obtained in all the varieties at Kachhiari as compared to Palampur could be
215
because of the difference in climate and soil type at the two locations.
Further, at Kachhiari more number of pickings were carried out as the crop
was of longer duration (April-August/September) than Palampur, where the
crop was of relatively shorter duration (May/June-September).
In the present study, although Shagun recorded higher incidence
of almost all the major pests, yet it gave higher yield. This can be attributed
to the tolerance phenomenon and higher yield potential of this variety.
Analogous observations were made by Shukla et al. (1998) at Jabalpur
(Madhya Pradesh) who described that even though varieties Ankur 35 and
Parbhani Kranti of okra registered significantly higher damage by E. vittella,
yet produced higher fruit yields.
Sharma and Dhankhar (1989) recorded lower yield from Harbhajan
and Pusa Makhmali as compared to other varieties at Hisar, thus
substantiating the current findings. Likewise, Raj et al. (1993) from Himachal
Pradesh obtained lower yield from Pusa Sawani variety as compared to other
varieties which is in agreement to the present results and ascribed the
severity of mosaic on Pusa Sawani variety responsible for its lower yield.
The data regarding higher yield of Varsha Uphar as compared to
Arka Anamika, Pusa Makhmali, Parbhani Kranti, Shagun and Harbhajan
recorded during the current investigation is in consonance with a study
carried out at Dhaulakuan, Himachal Pradesh (Anonymous, 1999). At
Hamirpur (Himachal Pradesh), Arka Anamika recorded highest yield followed
by Tulsi, Varsha Uphar, Shagun, Panchaali, Parbhani Kranti, Harbhajan and
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P-8 (Anonymous, 2004a) which is in close harmony to the existing results
although comparatively lower yield was recorded on all the varieties in the
present study. This could be because of the difference in time of sowing,
variety grown, environment, fertility status of the soil, pest and disease
pressure and agronomic practices carried out for the crop.
5.6 Field efficacy of insecticides and biopesticides against major insect-pests of okra
The indiscriminate use of chemical pesticides in agriculture has led
to adverse effects, such as the development of pesticide resistance, pest
resurgence, emergence of new pests, pollution and health hazards. In view
of such adverse effects, present studies were carried out to evaluate the
effectiveness of some insecticides alone or in combination with the microbial
pesticides and a parasitoid, T. chilonis for the management of major insect-
pests infesting okra at two locations i.e. Palampur and Kachhiari during the
two seasons.
5.6.1 Cotton jassid, A. biguttula biguttula
The results showed that cypermethrin proved most superior in
reducing the population of jassids on okra followed by endosulfan at both
the locations during both the seasons (Table 4.32-4.35). Both these
insecticides have proved their worth in the past in checking jassid population
on okra (Babu and Azam, 1982; Mohan and Mohan, 1985, Yadav et al.,
1988; Dahiya et al., 1990; Singh et al., 1991; Adiroubane and
Letchoumanane, 1998; Patel and Patel, 1998; Singh and Chaudhary, 2001;
Singh, 2007; Sinha and Sharma, 2007).
217
The treatments comprising azadirachtin and malathion showed
their effectiveness upto 9 days and were less effective than cypermethrin
and endosulfan. Dahiya et al. (1990) also reported the efficacy of malathion
against jassids on okra for a week whereas Jat (1981) observed malathion’s
effectiveness upto 12 days on okra. Malathion’s efficacy against okra jassids
has also been demonstrated by Singh (2007). Results in respect of lower
mortality of jassids afforded by malathion than synthetic pyrethroids in the
present study is in accordance with findings of Sucheta and Khokhar (1996).
Lower efficacy of neem based insecticide than synthetic
insecticides against A. biguttula biguttula in the present study is in
compliance with Thakur and Singh (1998) and Satpathy and Rai (1999).
However, Kumar and Singh (2001) and Mandal et al. (2006c) observed neem
based insecticides efficacious against jassid population on okra. This could
be because of the fact that the efficacy of an insecticide is related to the
number of its applications made, formulation and dosage used. The
moderate level of reduction because of azadirachtin in the current study
could be because of oviposition deterrent, repellent and growth inhibitory
action as has also been reported by Patel and Patel (1996) against okra
jassids.
Imidacloprid seed treatment and the combination treatment, B.
thuringiensis + endosulfan too showed consistently good performance in
suppressing A. biguttula biguttula population at different days after spray,
218
however, the former was found effective only at Palampur. This could be
because of the reason that seed treatment with imidacloprid has been
known to be effective against early sucking pests, since jassid population
appeared later at Kachhiari (in relation to date of sowing of crop), therefore,
by that time, the efficacy of seed treatment might have been reduced.
A number of workers have reported the efficacy of imidacloprid
seed treatment against sucking pests for variable period i.e. upto 60 days
after germination by Mote et al. (1993) in cotton, upto 35 days after
germination by Sreelatha and Divakar (1997) in okra, upto 40 days after
germination by Patil et al. (1999) in cotton, , upto 50 days after germination
by Bhargava and Bhatnagar (2001) in okra whereas, Singh et al. (1996)
observed the effectiveness of the same insecticide in cotton upto 121 days.
The effectiveness of imidacloprid seed treatment against okra
jassids has been acknowledged in the past (Mote et al., 1993; Mote et al.,
1994; Sharma and Kalra, 1996; Sreelatha and Divakar, 1997; Patil et al.,
1999; Bhargava and Bhatnagar, 2001; Kumar and Singh, 2001; Kumar et al.,
2001; Lal et al., 2001; Anonymous, 2005a; Sinha and Sharma, 2007).
The synergistic effect of B. thuringiensis with sub-lethal doses of
safer insecticides has been earlier demonstrated against a number of pests
by a number of workers (Puri et al., 1988; Dabi et al., 1989; Butter et al.,
1995; Sharma and Odak, 1996; Tomar, 1998; Patel and Vyas, 1999; Sharma,
219
2006). Mandal et al. (2006a) recorded minimum jassid population on okra in
B. thuringiensis + endosulfan treatment as compared to integration
treatment of B. thuringiensis with cartap, chlorpyriphos and amrutguard.
However, integration of imidacloprid with T. chilonis (both at half
dosages) did not prove effective. Mote et al. (1993) and Kumar and Singh
(2001) also observed that lower dose of imidacloprid (2.5 g kg -1 seed) was
not effective against A. biguttula biguttula. Moreover, T. chilonis is an egg
parasitoid of lepidopterous pests, therefore, it is quite obvious, that it must
have not parasitized eggs of jassids which is a homopteran pest. Also, T.
chilonis releases, B. thuringiensis, T. chilonis + B. thuringiensis and T.
chilonis + endosulfan were not found effective. The integrated treatment of
T. chilonis with B. thuringiensis and endosulfan did not show synergistic
effect since T. chilonis parasitizes eggs of only lepidopterous pests.
5.6.2 Cotton aphid, A. gossypii
In the present study, cypermethrin was the most effective
insecticide against okra aphids followed by endosulfan and B. thuringiensis +
endosulfan. Even azadirachtin and malathion were found effective but only
upto 9 days. Imidacloprid seed treatment also proved its efficacy but only at
Palampur (Tables 4.36-4.39). This is because of the early appearance of the
pest at Palampur (in relation to date of sowing of the crop) as compared to
Kachhiari, due to which the seed treatment might have been more
efficacious at the former location.
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The effectiveness of cypermethrin and endosulfan against A.
gossypii on okra has been acknowledged previously by many researchers in
their respective areas of study (Babu and Azam, 1982; Mohan and Mohan,
1985; Rai, 1985; Yadav et al., 1988; Rao et al., 1991; Bodhade et al., 1992;
Sosamma and Sheila, 1996; Patel et al., 1997b; Mishra, 2002; Sharma,
2004). Further, Ghosh et al. (1999) inferred high mortality of A. gossypii
(66.19%) on okra due to malathion.
Earlier also, imidacloprid seed treatment has been found effective
against okra aphids (Mote et al., 1993; Sreelatha and Divakar, 1997;
Anonymous, 2005a). A number of research workers (Dreyer and Hellpap,
1997; Chinniah and Ali, 2000; Mishra, 2002; Panickar et al., 2003; Mudathir
and Basedow, 2004) have reported the effectiveness of neem based
insecticides against A. gossypii on okra. In all these studies, 2 or more
applications of neem insecticides were made which resulted in good
suppression of aphid population. The lower efficacy of azadirachtin (upto
only 9 days) in the present investigation could be because of only single
spray made against this pest as against 2 or more sprays made by former
workers. Moreover, the effectiveness of a compound also varies with its
formulation, percentage of active ingredient, dosage, type of nozzle and
sprayer used.
The treatments which showed least worth against aphids in the
present study were T. chilonis, T. chilonis + imidacloprid, T. chilonis + B.
thuringiensis, B. thuringiensis and T. chilonis + endosulfan. Lower reduction
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evident in T. chilonis treatment either alone or in integration with B.
thuringiensis, endosulfan or imidacloprid was certainly because of the fact
that T. chilonis is an egg parasitoid of only lepidopterous pests, so obviously
it did not exhibit significant reduction either singly or in combination against
aphids. Also B. thuringiensis alone or in combination treatment did not prove
efficacious as B. thuringiensis has been known to infect mostly lepidopteran,
coleopteran and dipteran pests (Jaques, 1988; Biswas et al., 1996; Sharma
and Odak, 1996; Elanchezhyan et al., 2007) and A. gossypii, being a
homopteran pest experienced lower reduction in its population. Ghosh et al.
(1999) observed 35.35 per cent mortality of aphids on okra due to B.
thuringiensis.
5.6.3 Shoot and fruit borer, E. vittella
In the present study, cypermethrin and B. thuringiensis +
endosulfan showed least mean per cent fruit infestation by E. vittella at both
the locations during both the years (Table 4.40). The efficacy of
cypermethrin in checking population of shoot and fruit borer of okra is
corroborated by the findings of a number of earlier workers (Babu and
Azam, 1982; Krishnakumar and Srinivasan, 1984a; Krishnakumar and
Srinivasan, 1984b; Prasad et al., 1986; Gandhale et al., 1987; Singh and
Mishra, 1988; Peter and David, 1989; David and Kumaraswami, 1991; Shukla
et al., 1996; Rai and Satpathy, 1999; Ambekar et al., 2000b).
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The combination treatment of B. thuringiensis + endosulfan has
been found to be promising against E. vittella on okra by Tomar (1998) and
Mandal et al. (2006a). The present investigation also revealed the
effectiveness of endosulfan (although lower than cypermethrin) in lowering
the fruit infestation by shoot and fruit borer. This insecticide has been
reported effective against E. vittella in the past by many workers (Satpathy
and Mishra, 1970; Mote and Pokharkar, 1974; Uthamasamy and
Subramaniam, 1976; Verma et al., 1980; Sarkar and Nath, 1989;
Samuthiravelu and David, 1991; Pawar and Lawande, 1993; Gowri et al.,
2002; Manjanaik et al., 2002; Singh, 2007).
Other treatments which showed lower mean fruit infestation by E.
vittella were B. thuringiensis, T. chilonis + B. thuringiensis, azadirachtin and
malathion. The efficacy of B. thuringiensis and T. chilonis + B. thuringiensis
enhanced more by 15th day of spray, whereas that of azadirachtin and
malathion remained more effective for a week and their efficacy declined
thereafter. Taylor (1974), Krishnaiah et al. (1981), Mohan et al. (1983),
Singh et al. (1998), Tomar (1998), Ghosh et al. (1999), Patil et al. (2002)
and Gupta and Mishra (2006) have also observed the effectiveness of B.
thuringiensis against E. vittella on okra. The effectiveness of B. thuringiensis
upto 15 days after treatment against shoot and fruit borer on okra has been
formerly established by Satpathy and Panda (1997) thus, validating present
findings.
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The combination treatment of T. chilonis + B. thuringiensis was
found effective by Balakrishnan et al. (2004) in reducing the fruit damage by
another borer, H. armigera on cotton. The releases of T. chilonis against
shoot and fruit borer were not found much promising in the present study.
Similar observations regarding the lower efficacy of this parasitoid have been
made by Rao et al. (1978) and Sharma (2006). This could be ascribed to the
lower release rate (50,000 ha-1) of the parasitoid in the present study which
might have resulted in lower parasitism of eggs ultimately leading to
incomplete check in pest population. Sharma (2006) also mentioned similar
reasons for lower efficacy of T. chilonis against H. armigera on tomato.
Neem based insecticides have also shown their worth in checking
E. vittella incidence on okra formerly by Shukla et al. (1996) and Gajmer et
al. (2002). However, according to Sarode and Gabhane (1998), azadirachtin
was relatively ineffective in suppressing this pest. The difference in
efficiency of an insecticide could be ascribed to its formulation, percentage
of active ingredient, number of sprays and dosage used against the pest.
Malathion was reported effective earlier against E. vittella by Gupta and
Dhari (1978), Radke and Undirwade (1981), Verma (1985), Sarkar and Nath
(1989), Konar and Rai (1990), Shukla et al. (1996) and Singh (2007). The
comparatively higher performance of synthetic chemicals than neem based
insecticides against E. vittella as observed in the present study is in
accordance with the findings of Appaya (1990), Rao et al. (1991) and Shukla
et al. (1996).
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Imidacloprid seed treatment either alone or in integration with T.
chilonis at half dosages demonstrated poor performance against shoot and
fruit borers on okra. The present results find favour with Krishnaiah et al.
(1976) who noticed that okra seed treatment protected the crop from the
attack of E. vittella till the initiation of fruit set only which afterwards was
not found effective. Even Kumar et al. (1996) observed better reduction in E.
vittella infestation on okra by foliar applications rather than seed treatment.
5.6.4 Blister beetle, Mylabris spp.
In the current investigation, the synthetic pyrethroid, cypermethrin
undoubtedly proved to be the best in reducing Mylabris population on okra
followed by endosulfan. Even the integrated treatment of B. thuringiensis +
endosulfan performed consistently well against blister beetle. Moderate level
of protection (upto 9 days) was afforded by application of malathion and
azadirachtin. However, the remaining treatments viz. T. chilonis, B.
thuringiensis, imidacloprid, T. chilonis + imidacloprid, T. chilonis + B.
thuringiensis and T. chilonis + endosulfan illustrated lower efficacy against
this pest (Tables 4.41-4.44).
Literature pertaining to the effectiveness of synthetic chemicals
and biopesticides against blister beetle on okra is relatively scantly.
However, Kakar and Dogra (1988) and Kakar et al. (1990) validate the
present findings by reporting cypermethrin quite effective in reducing blister
beetle population in Himachal Pradesh on okra and French bean,
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respectively. Likewise, Chandel and Sood (1996) and Degri and Hadi (2000)
found cypermethrin highly efficacious against Mylabris beetles on cowpea
and rajmash, respectively. The efficacy of another synthetic pyrethroid viz.
lambda cyhalothrin has been illustrated by Sandal (2007) against M.
pustulata on pigeon-pea at Palampur (Himachal Pradesh).
Even the insecticide, endosulfan has been found to be promising in
suppressing blister beetle population previously by Kakar et al. (1990),
Chandel and Sood (1996) and Durairaj and Ganapathy (1999) on diverse
crops. The lower efficacy of malathion reported in the present study in
comparison to cypermethrin and endosulfan is corroborated by the findings
of Kakar et al. (1990), Chandel and Sood (1996), Degri and Chaudhary
(1998) and Degri and Hadi (2000).
5.6.5 Cotton leafroller, S. derogata
The present investigation revealed that the synthetic pyrethroid
cypermethrin proved best upto 9 days after spray, after which B.
thuringiensis + endosulfan was found more efficacious in reducing larval
population of S. derogata and remained effective even on 15 th day of spray.
In addition, other effective treatments were endosulfan, T. chilonis + B.
thuringiensis, B. thuringiensis, azadirachtin and malathion, the latter two
were effective upto 9 days of spray. On the other hand, the efficacy of T.
chilonis + B. thuringiensis, B. thuringiensis and B. thuringiensis + endosulfan
enhanced after 9 days of spray (Tables 4.45-4.48).
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The higher efficacy of cypermethrin than azadirachtin in checking
leafroller population on okra has been established earlier by Mishra et al.
(2002) in field trials conducted in Orissa. Sidhu and Dhawan (1979), Dhawan
et al. (1988) and Jafri et al. (1988) found endosulfan effective against
leafroller on cotton crop, thus supporting the current results.
The effectiveness of B. thuringiensis in suppressing S. derogata
population on okra has also been acknowledged earlier by Taylor (1974) and
Obeng and Sackey (2003). Neem based compounds have also proved their
capability in suppressing leafroller population in the past as reported by
Cobbinah and Owusu (1988), Anaso and Lale (2002) and Obeng and Sackey
(2003).
5.7 Effect of insecticides and biopesticides on marketable yield of okra All the insecticidal and biopesticidal treatments gave significantly
higher yield of okra over untreated check. The two year data at two
locations (Table 4.49) revealed that cypermethrin registered highest
marketable yield (100.29 to 127.40 q ha-1) whereas T. chilonis registered
lowest yield (48.76 to 66.62 q ha-1) of okra fruits. The other treatments
which recorded higher fruit yield were endosulfan, B. thuringiensis +
endosulfan, azadirachtin, imidacloprid and malathion (78.47 to 116.46 q
ha-1).
A number of research workers have reported higher yield of okra
fruits by the application of cypermethrin through reduction in the population
of various pests on this crop (Babu and Azam, 1982; Patel et al., 1984; Rai,
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1985; Gandhale et al., 1987; Narke and Suryawanshi, 1987; David and
Kumaraswami, 1991; Shukla et al., 1996; Singh and Chaudhary, 1999).
Likewise, worth of endosulfan in checking pest population on okra and giving
higher yields has been illustrated previously by Uthamasamy and
Subramaniam (1976); Jadhav and Nawale (1980); Verma et al. (1980);
Khaire and Naik (1986); Rao et al. (1991); Samuthiravelu and David (1991);
Singh et al. (1991); Patel et al. (1997b); Kumar and Singh (2001) and
Manjanaik et al. (2002).
The integrated treatment of B. thuringiensis + endosulfan was
reported effective in suppressing population of borers and jassids on okra
leading to higher fruit yield (Tomar, 1998; Mandal et al., 2006a). The higher
okra yield obtained from malathion treatment is in line with the findings of
Sarkar and Nath (1989), Konar and Rai (1990) and Borah (1995) because of
its efficacy in checking population of sucking, foliage and fruit pests. The
results pertaining to higher marketable yield obtained from endosulfan as
compared to neem based products is in consonance with research results of
Rao et al. (1991) and Patel et al. (1997b).
According to Mohan et al. (1983), Singh et al. (1998) and Gupta
and Mishra (2006), B. thuringiensis treatment checked borer incidence and
registered higher yield of okra, thus substantiating the current findings. Even
the imidacloprid seed treatment was found effective in enhancing okra yield
in the present study, by causing reduction in the population of sucking
pests. In the past also, comparable observations regarding efficacy of
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imidacloprid seed treatment have been made (Jotwani and Sarup, 1966;
Mote et al., 1993, Mote et al., 1994; Sreelatha and Divakar, 1997; Bhargava
and Bhatnagar, 2001; Dikshit et al., 2002; Anonymous, 2005a; Sinha and
Sharma, 2007).
