INTEGRATED APPLICATION OF INSECTICIDE AND FUNGICIDE TO CONTROL OkYVCMV AND PSEUDOCERCOSPORA LEAF SPOT OF OKRA SEED CROPS

Authors: M. G. Kibria1 and I. H. Mian2

Abstract

G. Kibria and I. H. Mian. 2013. Integrated application of insecticide and fungicide to control OkYVCMV and Pseudocercospora leaf spot of okra seed crops. Bangladesh J. Plant Pathol. 29 (1&2):33-38.

A field experiment was conducted to test the efficacy of integrated application of pesticides to control Okra yellow vein clearing mosaic virus (OkYVCMV) and Pseudo-cercospora leaf spot caused by Pseudocercospora abelmoschi (PLS) of okra seed crop, and to increase yield and quality of okra seeds. All pesticidal treatments gave considerable reduction over control in incidence of OkYVCMV, severity of PLS, and population of whitefly (Bemisia tabaci). The reduction over control was 55.95, 43.33, 35.35 and 21.02% in OkYVCMV incidence and 89.18, 72.45, 62.36 and 31.52% in PLS due to treatments T1= pre-sowing seed treatment with Gaucho 72 WS (Imidacloprid) at 5 g/kg seed + soil treatment with Furadan 5G (Carbofuran) at 30 kg/ha)+ 4 foliar sprays with Admire

(Imidacloprid) at 1 ml/L+ 4 foliar sprays with Emivit 50 WP at 3 g/liter, T2=seed treatment with Gaucho 72 WS+ 4 foliar sprays with Admire + 4 foliar sprays with Emivit 50 WP, T3=seed treatment with Gaucho 72 WS+ 4 foliar sprays with Emivit 50 WP, and T4=seed treatment with Gaucho 72 WS, respectively. Reduction in population of whitefly due to the pesticidal treatments were 69.06, 58.39 and 17.78% at 30 days after sowing, and 73.90, 65.76 and 40.29% at 60 days after sowing. The treatments improved plant growth, pod and seed yield and seed quality considerably. The seed yield was increased by 133.22, 80.54, 64.91 and 23.05% over control due to the treatments. The best treatment was T1 to control both diseases and to improve yield and quality of seeds.

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INTRODUCTION 

Okra, also known as lady’s finger (Abelmoschus esculentus L.) is one of the popular vegetable crops in Bangladesh. It is cultivated throughout the year except 3-4 cool months. It suffers from a number of diseases caused by fungi, bacteria, nematode and viruses (Talukdar 1974, Fakinr 2000, Rangaswami and Mahadevan 2006). Among them, Okra Yellow Vein Clearing Mosaic Virus (OkYVCMV) and Psudocercospora leaf spot (P. abelmoschi) are two major diseases. OkYVCMV infects at all growing stages of okra causing severe reduction in plant growth and yield. The disease is transmitted by the vector whitefly (Bemisia tabaci). Plants infected at early stages remain stunted. The fruits of the infected plant exhibit pale yellow color, deformed, small and tough in texture. Seeds of infected plants are smaller and shriveled. If the plants are infected within 20 days after germination (DAG), the yield loss may be up to 94%. Infection of plants at 50 and 60 DAG may cause 84 and 49% yield losses, respectively (Sastry and Singh 1974).

 Attempt was made by many researchers to control the disease through insect vector control and found that application of insecticide minimized whitefly population and the incidence of OkYVCMV (Pun et al. 2005a, 2005b, Gowdar et al. 2007). Significant reduction  in  OkYVCMV  incidence  and  whitefly populations was achieved with foliar spray of Aceta- miprid,   Dimethoate,   Imidacloprid,  Meta-systox, Monocrotophos, Nuvacron, Thiamethoxam, Triazo Ahmed et al. 2001, Misra 2005, Gowdar et al. 2007). Pesticidal seed treatment with insecticide (Imidacloprid) (Praveen et al. 2007) and soil application of Carbofuran at the time of sowing are effective measures to control OkYVCMV through its vector suppression (Murthy and Reddy 1992, Praveen et al. 2007).

Pseudocercospora leaf spot (PLS) of okra caused by Pseudocercospora abelmoschi is prevalent in late summer and early winter.  The disease may cause severe problem in seed crop causing smaller fruits and shriveled seeds. Spraying okra field with 500 g Zineb or Maneb suspended in 250 liters of water at 15 days interval after the first appearance of the symptoms proved effective for controlling Pseudocercospora leaf blight disease. The best control of P. abelmoschi was obtained from foliar spray of Copper oxychloride, followed by Carbendazim and Mancozeb. Carbendazim gave the highest yield increase, followed by Copper Oxychloride and Mancozeb (Srivastava et al. 1992, Rahman et al. 2000).

Both OkYVCMV and Pseudocercospora leaf spot are common in Bangladesh (Talukdar 1974). These are considered as serious diseases of okra, especially when it is grown in late summer. Comprehensive research has not yet been accom-plished in the country to find out effective control methods against the diseases. Available literature reveal that effective control of OkYVCMV and Pseudocercospora leaf spot may be achieved through vector control using insecticides and foliar spray with fungicides, respectively. Integrated application of the pesticides may give better control compared to application of either insecticides or fungicides. Present piece of research was conducted to test the efficacy of integrated application of insecticide and fungicide to control OkYVCMV and Psuedocercospora leaf spot of okra.

MATERIALS AND METHODS

An experiment was conducted to test the efficacy of three insecticides and a fungicide applied in an integrated approach to control Okra Yellow Vein Clearing Mosaic Virus (OkYVCMV) and Psuedocercospora leaf spot (Pseudocercospora abelmoschi) of okra.  Three insecticides namely Gaucho 72 WS (Imidacloprid), Furadan 5G (Carbofuran) and Admire (Imidacloprid) were applied to control OkYVCMV through vector control, and the fungicide Emivit 50 WP was used to control Psuedocercospora leaf spot. Individual components of treatments in the present experiment were: C1 = Pre-sowing insecticidal seed treatment with Gaucho 72 WS (Imidacloprid) @ 5 g/kg seed, C2 = Pre-sowing soil treatment with Furadan 5G (Carbofuran) @ 30 kg/ha), C3 = Four foliar sprays with Admire (Imidacloprid) @ 1 ml/L, and C4 = Four foliar sprays with Emivit 50 WP @ 3 g/liter. Spraying of Admire was started from 15 DAS and continued for 4 times at 15 days interval. Furadan 5G was applied in the furrows at sowing. Seeds were treated with the insecticide just before sowing. Spray of fungicide was started when symptoms of PLS appeared and continued for 4 times with 7 days interval. The integrated treatments, T1= C1+ C2+ C3+ C4, T2= was C1+C3+ C4, T3= C1+ C4 and T4= C1. An additional treatment T5 was maintained which received neither insecticide nor fungicide and served as control.

The experiment was conducted in the experimental farm of Bangabandhu Sheikh Mujibur Rahman Agrilcultural Univeristy (BSMRAU), Gazipur during 2009. The experiment was laid out following randomized complete block design with three replications. The unit plot size was 4.5 m × 1.2 m. Drains of 50 cm width and 30 cm depth were dug around each unit plot for maintaining isolation distance as well as facilitating irrigation and drainage of excess water. The experimental field was prepared properly for good tilth following standard practices (Razzaque et al. 2000). Fertilizers were applied @ 50-24-30-10-1-0.5 kg of N-P-K-S-Zn-B per hectare, respectively (Anon. 2005). Manure was applied as cowdung at the rate of 4 t/ha. The entire quantity of cowdung, P, K, S, Zn and B and half of N were applied at the time of final land preparation. Remaining N was applied around the base of the plant as top dressing and incorporated with soil at 3rd and 5th week after sowing. A previously selected susceptible okra genotype was used in the experiment. Seeds of the genotype were soaked in tap water for 12 hours, air dried and treated with Gaucho 72 WS. Treated seeds were sown in the field maintaining plant to plant and row to row distances of 60 and 50 cm, respectively. After 6 to 7 days of germination, the seedlings were thinned to have one plant per hill. If any seedling died within three weeks of germination it was replaced by seedling of same age raised in polyethylene bags (9 x 15 cm). Irrigation was applied after each top dressing of urea and whenever necessary. Every time, irrigation was followed by mulching and weeding. Other necessary intercultural operations were done throughout the cropping season for proper growth and fruit production (Razzaque et al. 2000).

Data on incidence of OkYVCMV was recorded on 60 days after sowing (DAS). Number of diseased and healthy plants in each unit plot was counted. Incidence of OkYVCMV was expressed in percentage based on total number of plants checked. The disease incidence (DI) was computed following a formula as shown below:

       integrated-application-of-insecticide-and-fungicide-to-control-okyvcmv-and-pseudocercospora-leaf-spot-of-okra-seed-crops-1

Data on whitefly population was also recorded. To count population of adult whitefly, five plants were selected randomly from each unit plot and 5 leaves were selected from each plant at different nodal positions (one at the top, two in the middle and two at the bottom). The counts were taken in the morning when whiteflies are less active as suggested by Basu (1995). Number of whitely per leaf was counted at 30 and 60 DAS. Precaution was taken not to disturb the insect at the time of counting. Severity of Pseudocercospora leaf spot (PLS) was indexed on a 0-8 scale as suggested by Rahman and Nahar (1990) at 60 DAS. Percent Disease Index (PDI) for the leaf spot was computed according to the following formula as described by Mian (1995):

                    integrated-application-of-insecticide-and-fungicide-to-control-okyvcmv-and-pseudocercospora-leaf-spot-of-okra-seed-crops-2

Data on plant growth, seed yield, selected yield contributing parameters, and seed quality were also recorded. Quality of seeds in terms of germination, seedling growth and vigor index were determined following methods of International Seed Testing Association (ISTA) (Anon. 1996). Seedling vigour was determined using a standard formula (Baki and Anderson, 1972) viz.

Vigour Index = (mean root length + mean shoot length) x percent emergence.

Fully ripened pods were collected from each of the unit plot and seeds were separated from the pods, sun dried and cleaned. Seed yield per plant were computed. Recorded data were subjected to statistical analysis following standard procedure (Gomez and Gomez 1984) using MSTAT-C statistical software. Whenever necessary, data were transformed using ArcSin transformation method before performing analysis of variance.

RESULTS AND DISCUSSION

Incidence of OkYVCMV

Incidence of OkYVCMV on okra seed crop varied from 28.31 to 64.27% under different treatments including control (T1 to T5). The highest incidence of the disease was recorded from control plot. All pesticidal treatments (T1 to T4) caused significant reduction in disease incidence over control. The reduction over control was 55.95, 43.33, 35.35 and 21.02% respectively under treatments T1, T2, T 3 and T 4 (Table 1).

Severity of Pseudocercospora leaf spot (PLS)

The percent disease index (PDI) of PLS on okra in plots under different treatments including control ranged 5.64-52.12. The highest disease severity was found under control. Like OkYVCMV, PDI of PLS was also significantly reduced due to application pesticidal treatments (T1 to T4) compared to control. The reductions over control were 89.18, 72.45, 62.36 and 31.52% under T1, T2, T 3 and T 4 treated plots, respectively (Table 1).

Population of whitefly

Average populations of whitefly on okra seed crop ranged from 0.91-2.98 per leaf at 30 DAS and 1.25-4.79 per leaf per plant at 60 DAS recorded on five treatment approaches (T1 to T4) including control (T5). Treatments T1, T2 and T3 significantly reduced the whitefly populations over control (T5). The maxi-

mum  reduction was achieved by T1 treated plot followed by T2 and T3 showing 69.06, 58.39 and 17.78% reduction over control at 30 DAS, and 73.90, 65.76 and 40.29% at 60 DAS, respectively (Table 2).

Plant height and Fruit yield per plant

Plant height of the seed crop was 105.89, 97.90, 93.80, 90.01 and 84.12 cm found in the plots treated with T1 to T5, respectively. All pesticidal treatment increased plant height significantly over control. The maximum increase was obtained in T1 treated plot followed by T2, T3 and T4 treated ones (Table 3).

Number of fruits per plant under the T2, T 3, T4 and T5 was 16.11, 13.83, 13.15, 11.91 and 10.44, respectively. Significant increase in fruit yield was obtained with all the pesticidal treatments (T1 to T4). Differences in number of fruit per plant were significant (Table 3).

Seed number per fruit and per plant, seed yield, seed size and Seed quality

All qualitative parameters of seeds in terms of germination, seedling growth and seed vigor were improved tremendously due to application of all pesticidal treatments. The lowest number of seeds per fruit was found in treated control plots (T5). The fruit number increased significantly over control due to application of the treatments T1 to T4. The highest fruit yield was obtained from T1 treated plot followed by T2 and T4 treated plots showing 59.96, 56.39, 55.16 and 49.59 seeds per fruit. The lowest seed number of 476.63 seeds per plant was harvested from control plot. It was increased to 965.90, 779.81, 725.17 and 590.82 due to pesticidal treatments T1, T2, T3 and T4, respectively. The increase was significant compared to control (Table 3).

Seed yield was 56.44, 43.69, 39.91, 31.23 and 24.20 g/plant in plots treated with different treatments (T1, T2, T3 and T4). Significantly the highest seed yield was achieved with all pesticidal treatments over control. The yield increase in T1, T2, T3 and T4 treated plots was 133.22, 80.54, 64.91 and 23.05%, respectively. Seed size in terms of 1000-seed weight increased significantly over control (T5) due to four pesticidal treatments (T1,- T4). The maximum increase in 1000-seed weight was achieved with T1 followed by T2, T3 and T4 showing 1000-seed weight of 58.43, 56.03, 55.03 and 52.85 g, respectively. (Table 4).

Shoot and root length and Seed vigour index

The root and shoot length ranged from 6.04-13.05 cm and 5.32-9.59 cm, respectively obtained in different treated plots. Both the parameters were significantly higher in all four pesticidal treated plot compared to untreated control plot. The highest shoot and root length were found in the plot treated with T1 followed by T2, T3, T4 and T5 treated plots (Table 5).

  integrated-application-of-insecticide-and-fungicide-to-control-okyvcmv-and-pseudocercospora-leaf-spot-of-okra-seed-crops-3

integrated-application-of-insecticide-and-fungicide-to-control-okyvcmv-and-pseudocercospora-leaf-spot-of-okra-seed-crops-4

integrated-application-of-insecticide-and-fungicide-to-control-okyvcmv-and-pseudocercospora-leaf-spot-of-okra-seed-crops-5

The vigour of seedling raised from seeds harvested from the plots of different treatment viz., T1, T2, T3, T4 was 1838.09, 1513.17, 1239.34, 1075.88 and 732.61, respectively. The parameters under all pesticidal treatments were significantly higher compared to control (T5). The highest seedling vigour was found under the treatment T1 followed by T2, T3, and T4 (Table 5).

BCR

Fruit yield per hectare varied ranged 6.38-10.79 tons under five treatments. The BCR recorded under five treatments including control ranged 1.39-1.84. The highest fruit yield as well as BCR was obtained with T1 followed by T2, T3 and T4. Effect of the treatments on all parameters were not significantly different (Table 6).

Results of the present study reveal that pre-sowing insecticidal seed treatment with  Gaucho 72

WS (Imidacloprid) @ 5 g/kg seed, insecticidal soil treatment with Furadan 5G (Carbofuran) @ 30 kg/ha) at sowing, 4 foliar insecticidal spray with Admire (Imidacloprid) @ 1 ml/L and 4 foliar fungicidal spray with Emivit 50 WP @ 3 g/liter applied to okra seed crop in integrated approaches gave significant decrease in incidence of OkYVCMV, PLS, and population of whitefly (Bemisia tabaci) over control. The treatments gave significant improvement in plant growth, pod and seed yield and seed quality. Chakraborty and Mukhopadhyay (1977), Khan and Mukhopadhyay (1985), Anju et al. (1993),  Singh et al. (1998), Rana et al. (2006) and Praveen et al. (2007) tested insecticidal measures to control OkYVCMV and found effective results. Rahman et al. (2000) reported successful control of PLS with fungicidal spray and obtained higher seed yield of okra. But none of the investigator tested the control measures in integrated approaches.

integrated-application-of-insecticide-and-fungicide-to-control-okyvcmv-and-pseudocercospora-leaf-spot-of-okra-seed-crops-6

integrated-application-of-insecticide-and-fungicide-to-control-okyvcmv-and-pseudocercospora-leaf-spot-of-okra-seed-crops-7

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1Senior Scientific Officer, Plant Pathology Section, HRC, BARI, 2Professor, Department of Plant Pathology, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, Bangladesh
(The paper is a part of M.Ph thesis of the first author)

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