Effect of abiotic factors on population of aphid and damage by shoot & fruit borer in okra during summer and kharif season at Anand in Gujarat

A field experiment was conducted at Anand Agricultural University, Anand, Gujarat to study the impact of weather variables on population dynamics of aphid, Aphis gossypii and shoot & fruit borer, Earias vittella in summer and kharif okra for two consecutive years (2005-06 and 2006-07). Peak activity of aphid population was found during 12 th & 14 th and 13 th & 15 th Meteorological Standard Week (MSW) whereas, the peak infestation to fruits due to E. vittella observed in the 13 th & 15 th and 29 th & 32 nd MSW during summer and kharif season, respectively. Bright sunshine hours, temperature (maximum and minimum), vapour pressure (morning and evening) and wind speed had significant positive effect on population of aphid during summer season, while Bright sunshine hours, maximum temperature and temperature range showed significant negative impact with aphid population during kharif season. Maximum and minimum temperature had significantly negative effect, while morning and evening relative humidity significant positive effect on fruit damage due to E. vittella during kharif season. However, per cent fruit damage showed significant positive impact with BSS, temperature (maximum and minimum) and vapour pressure deficit (morning and evening) during summer season.

shoot & fruit borer was carried out for two consecutive years (2005-06 and 2006-07) on organically and inorganically cultivated okra (variety Gujarat Okra-2). The okra crop was raised organically and inorganically, each in area of 20 x 10 m with a spacing of 45 x 30 cm and 60 x 30 cm for summer and kharif season, respectively at Agronomy Farm, B. A. College of Agriculture, Anand Agricultural University, Anand. In order to maintain the organic conditions, F.Y.M @ 12 tonnes/ha was applied in the plot, whereas in other plot N: P: K @ 100: 50 :50 kg/ ha (basal application N: P: K @ 50: 50 :50 kg/ha & split application at flowering stage N: P: K @ 50: 0 : 0 kg/ha) was applied to create the inorganic condition. The experiment plots (organic and inorganic) were divided into 10 equal quadrates and 25 plants were randomly selected in each quadrate to record observations on aphid population on three leaves (top, middle and bottom) per plant at weekly interval starting from germination to harvest of the crop. The per cent fruit damage was worked out on the basis of number of healthy and damaged fruits at every picking. The data on aphid population and per cent fruit damage were correlated with different weather factors recorded following meteorological standard weeks (MSW).

Aphid, A. gossypii
The incidence of A. gossypii on okra crop commenced at 8 th and 23 rd MSW (2 nd WAS) and continued almost throughout the crop period in summer and kharif okra, respectively (Table 1). The pest population fluctuated during early part of crop growth, increased gradually from 11 th MSW (5 th WAS) and attained its peak at the end of crop i.e. 19 th and 20 th MSW (13 th & 14 th WAS) in summer crop. During kharif season, this pest attained its peak activity in 29 th and 32 nd MSW (8 th and 11 th WAS). The aphid population was relatively low in organically grown crop as compared to inorganically grown crop. However,

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the trend of its occurrence was more or less same in organic and inorganic crops. These finding is in agreement with the report of Narangalkar (2003).
Significant positive association between aphid population and sunshine hours was noticed (r = 0.689** and 0.682** for organic and inorganic crop, respectively) during summer season, while the significant negative association (r = -0.784** and -0.815** for organic and inorganic crop, respectively) found during the kharif season. The more or less same trend was observed for maximum and minimum temperature in organic and inorganic crop during both the seasons. Relative humidity did not show any notable influence on aphid incidence in summer, while kharif, it showed significant positive correlation. Significant positive relationship was found between the summer aphid population and vapour pressure (morning and evening) in both the crops (organic and inorganic). Vapour pressure deficit influenced positively on occurrence of aphids. Wind speed showed significant positive relationship with aphid population during both the season. Significant negative correlation was established between aphid population and temperature range in pooled analysis in both the season. respectively. These observation is in close agreement with the report of Araujo and Sales (1985). The study also showed significant negative correlation between aphid population on okra and temperature range. Almost similar findings were supported by Jondhale (2007).

Shoot and fruit borer, E. vittella
The data summarized in Table 1 revealed that incidence of this pest increased in organic as well as inorganic crop at 5 th WAS (11 th & 26 th MSW) during both the seasons. First and second peak was during 7 th & 8 th (13 th & 29 th MSW) and 13 th & 11 th (19 th & 32 nd MSW) WAS, respectively during summer and kharif season. Thus, incidence of fruit borer was found to be low in okra grown organically than inorganically. Sharma et al. (2010) have also reported peak level of infestation during 29 th MSW in okra at Udaipur, India.
The bright sunshine hours had significant negative impact with fruit infestation in organic as well as inorganic crops during kharif season, while it was found to be positive with bright sunshine hours. The maximum and minimum temperatures were negatively correlated with infestation by E. vittella, while morning and evening relative humidity had significant positive correlation with the incidence of shoot and fruit borer during kharif season. However, significant negative impact was found with above mentioned weather parameters during summer season. However in none of the cases, vapour pressure during morning hours had significant impact. Vapour pressure deficit (morning and evening) showed significant negative and positive impact with the fruit borer incidence during kharif and summer season, respectively. Temperature range showed negative impact in both the seasons. The present results are in the report of agreement with Sharma et al. (2010).
The regression study revealed that maximum temperature found to be effective weather parameters

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during both the seasons of study.

CONCLUSION
Population of aphid, A. gossypii recorded in two different types of okra crops (organic and inorganic) indicated that incidence of the pest commenced from fifteen days after sowing and continued more or less throughout the crop period in both the crops and seasons. Incidence of fruit borer, E. vittella to okra after one month of sowing and remained at higher level during 7 th (29 th & 13 th MSW) to 13 th and 9 th (32 th & 15 th MSW) WAS in kharif and summer season, respectively (inorganically and organically grown crop). Bright sunshine hours, maximum and minimum temperature, evening vapour deficit and wind speed showed significant positive relationship with aphid population during summer season. However, Bright sunshine hours, maximum temperature and temperature range was found to be significant negative impact with aphid population during kharif season. Bright sunshine hours and temperature (maximum and minimum) had significant negative effect, while humidity (morning and evening) and evening vapour pressure had significant positive effect on damage by E. vittella. However, per cent fruit damage showed significant positive impact with BSS, temperature (maximum and minimum) and vapour pressure deficit (morning and evening) during summer season.