Background

Grape (Vitis vinifera L.) is one of the most important commercial fruit crops of sub-tropical, tropical and temperate regions of the world. In India, the states like Maharashtra, Karnataka, Tamil Nadu, Andhra Pradesh, Punjab, Madhya Pradesh and Haryana are the major grape growing areas. According to the reports of Butani (1979) more than 85 species of insect pests are noticed on grapes in India. From northern Karnataka, Balikai and Kotikal (2003) documented 26 pests on grapevines. Among these, two insects viz., flea beetle and mealy bug were recorded as major pests. In addition, thrips and mites also cause heavy damage affecting berry quality.

Due to continuous and indiscriminate use of synthetic insecticides, there is a development of resistance to insecticides and hence the efficacy has become less reliable. To overcome this problem discovery of novel insecticides with different biochemical targets are needed. New insecticidal molecules have been evaluated against insect pests of grapevine by many researchers (Balikai, 2007; Balikai and Patil, 2007; Balikai, 2016; Prema et al., 2016; Patil et al., 2017). Novel molecules are effective at low dosages and have less exposure in the environment. Fipronil 80 WG is one such insecticide which was effective against thrips in grapes (Niranjana, 2008; Prema et al., 2016; Patil et al., 2017) and leaf folder in rice (Prema et al., 2017). Thus, fipronil 80 WG, a promising Phenyl Pyrrozole insecticide was evaluated against grape thrips in comparison with selected insecticides like imidacloprid 200 SL, spinosad 45 SC and Standard check (Monocrotophos 36 WSC @ 360 g a.i./ha followed by Dimethoate 30 EC @ 521 g a.i./ha).

1 Materials and Methods

During two consecutive seasons of 2006-07 and 2007-08, the field experiments were carried out at the Horticultural Research Station, Bijapur (Tidagundi), Karnataka, India with nine treatments (Table 1) and three replications laid out in a randomized block design. The study was conducted on medium black soils with Thompson Seedless variety which was planted at a spacing of 3.03 x 1.51 m in a telephone system. The gross and net plot sizes for each treatment were 3.03 x 10.57 m and 3.03 x 7.55 m with seven and five vines, respectively. The vines were pruned during April and October months every year. 

Two insecticidal applications were given at ten days interval in the month of January during both the years with the help of knapsack sprayer using spray volume of 1,000 litres per hectare. The efficacy of insecticidal treatments was assessed by recording the number of thrips present on three leaves per plant from five vines in each treatment. Mean number of thrips per leaf was worked out. These observations were made at one day before first spray as pre-treatment count and on third, seventh and tenth day after each application as post-treatment counts. The observations made on tenth day after first spray served as pre-treatment count for the second spray. The per cent protection against thrips over untreated check was worked out. The per cent reduction in thrips population over pre-treatment count was also worked out. The fruits from net plots were harvested separately and fruit yield per vine was computed. 

The observations on phytotoxicity symptoms (viz., leaf tip and surface injury, wilting, vein clearing, necrosis, epinasty and hyponasty) were recorded on first, third, fifth, seventh and tenth day after first and second sprays by using 0-10 score (Balikai, 2016).

2 Results and Discussion

2.1 First year: Bio-efficacy against thrips, Scirtothrips dorsalis Hood and Thrips palmi Karny

2.1.1 First spray

A day before insecticidal treatments, the thrips population varied from 9.4 to 10.7 per leaf with non-significant differences among various treatments. 

At three days after first spray, Fipronil 80 WG @ 50 g a.i./ha recorded lowest population of 6.2 thrips per leaf followed by Fipronil 80 WG @ 40 g a.i./ha (6.4 thrips/leaf) and Fipronil 5 SC @ 40 g a.i./ha (7.2 thrips/leaf) and were equally effective against thrips. The latter treatment was on par with Spinosad 45 SC @ 84.375 g a.i./ha, Imidacloprid 200 SL @ 45 g a.i./ha and Standard check (Monocrotophos 36 WSC @ 360 g a.i./ha followed by Dimethoate 30 EC @ 521 g a.i./ha) with 8.3, 8.5 and 8.6 thrips per leaf, respectively. 

At seven days after first insecticidal spray, Fipronil 80 WG @ 50 g a.i./ha recorded lowest population of 4.8 thrips per leaf followed by Fipronil 80 WG @ 40 g a.i./ha (5.1 thrips/leaf) and Fipronil 5 SC @ 40 g a.i./ha (5.8 thrips/leaf) and remained equally effective against thrips. The latter treatment was on par with Spinosad 45 SC @ 84.375 g a.i./ha and Imidacloprid 200 SL @ 45 g a.i./ha with 5.8 and 6.5 thrips per leaf respectively which in turn were on par with Standard check (Monocrotophos 36 WSC @ 360 g a.i./ha followed by Dimethoate 30 EC @ 521 g a.i./ha). Similar trend continued even at 10 days after first spray (Table 1). 

2.1.2 Second spray 

At three days after second insecticidal spray, Fipronil 80 WG @ 50 g a.i./ha and 40 g a.i./ha recorded lowest population of thrips (2.6 and 2.8 thrips/leaf, respectively) indicating their higher and equi-effectiveness. The next best treatment was Fipronil 5 SC @ 40 g a.i./ha with 3.9 thrips/leaf and was on par with Spinosad 45 SC @ 84.375 g a.i./ha and Imidacloprid 200 SL @ 45 g a.i./ha with 4.7 and 4.5 thrips per leaf, respectively. The latter two treatments were on par with Standard check (Monocrotophos 36 WSC @ 360 g a.i./ha followed by Dimethoate 30 EC @ 521 g a.i./ha) with 5.5 thrips per leaf. 

At seven days after second insecticidal spray, Fipronil 80 WG @ 50 g a.i./ha and 40 g a.i./ha recorded lowest population of thrips (1.5 and 1.2 thrips/leaf, respectively) indicating their higher and equi-effectiveness. The next best treatment was Fipronil 5 SC @ 40 g a.i./ha with 2.7 thrips/leaf and was on par with Imidacloprid 200 SL @ 45 g a.i./ha with 3.5 thrips per leaf. The latter treatment was on par with Spinosad 45 SC @ 84.375 g a.i./ha and Standard check (Monocrotophos 36 WSC @ 360 g a.i./ha followed by Dimethoate 30 EC @ 521 g a.i./ha) with 3.8 and 4.0 thrips per leaf, respectively.

At ten days after second spray, Fipronil 80 WG @ 50 g a.i./ha, 40 g a.i./ha and Fipronil 5 SC @ 40 g a.i./ha recorded lowest population of thrips (0.4, 0.5 and 0.9 thrips/leaf respectively) indicating their higher and equal effectiveness. The next best treatments included Imidacloprid 200 SL @ 45 g a.i./ha, Spinosad 45 SC @ 84.375 g a.i./ha and Standard check (Monocrotophos 36 WSC @ 360 g a.i./ha followed by Dimethoate 30 EC @ 521 g a.i./ha) with 1.2, 1.4 and 1.6 thrips per leaf, respectively (Table 1).

2.2 Second year

2.2.1 First spray

At one day before insecticidal spray, the thrips population varied from 11.3 to 12.6 per leaf with non-significant differences among various treatments (Table 2). 

At three days after first spray, Fipronil 80 WG @ 50 g a.i./ha recorded lowest population of 8.1 thrips per leaf followed by Fipronil 80 WG @ 40 g a.i./ha (8.6 thrips/leaf), Fipronil 5 SC @ 40 g a.i./ha (9.6 thrips/leaf) and Spinosad 45 SC @ 84.375 g a.i./ha (9.8 thrips/leaf) and were equally effective against thrips. The latter two treatment were at par with Standard check (Monocrotophos 36 WSC @ 360 g a.i./ha followed by Dimethoate 30 EC @ 521 g a.i./ha) with 11.2 thrips per leaf (Table 2). 

At seven days after first spray, Fipronil 80 WG @ 50 g a.i./ha recorded lowest population of 6.2 thrips per leaf followed by Fipronil 80 WG @ 40 g a.i./ha (6.4 thrips/leaf) and were highly effective against thrips. The latter treatment was at par with Fipronil 5 SC @ 40 g a.i./ha (7.5 thrips/leaf). The treatments viz., Spinosad 45 SC @ 84.375 g a.i./ha, Imidacloprid 200 SL @ 45 g a.i./ha and Standard check (Monocrotophos 36 WSC @ 360 g a.i./ha followed by Dimethoate 30 EC @ 521 g a.i./ha) with 8.5, 8.8 and 9.6 thrips per leaf, respectively were at par with each other and were significantly superior to untreated check (Table 2).

At ten days after first spray, Fipronil 80 WG @ 50 g a.i./ha recorded lowest population of 4.2 thrips per leaf followed by Fipronil 80 WG @ 40 g a.i./ha (4.7 thrips/leaf) and were at par with each other. The next best treatments included Fipronil 5 SC @ 40 g a.i./ha (6.4 thrips/leaf) and Spinosad 45 SC @ 84.375 g a.i./ha (7.5 thrips/leaf). The treatments viz., Imidacloprid 200 SL @ 45 g a.i./ha and Standard check (Monocrotophos 36 WSC @ 360 g a.i./ha followed by Dimethoate 30 EC @ 521 g a.i./ha) with 7.8 and 8.3 thrips per leaf, respectively were at par with each other and were significantly superior to untreated check in reducing the trips population (Table 2). 

2.2.2 Second spray

At three days after second spray, Fipronil 80 WG @ 50 and 40 g a.i./ha recorded lowest population of thrips (3.0 and 3.4 thrips/leaf, respectively) indicating their higher effectiveness as compared to any other treatment. The next best treatment was Fipronil 5 SC @ 40 g a.i./ha with 5.2 thrips/leaf. The treatments Spinosad 45 SC @ 84.375 g a.i./ha and Imidacloprid 200 SL @ 45 g a.i./ha with 6.4 and 7.2 thrips per leaf, respectively were at par with each other. The latter treatment was at par with Standard check (Monocrotophos 36 WSC @ 360 g a.i./ha followed by Dimethoate 30 EC @ 521 g a.i./ha) with 7.8 thrips per leaf. 

At seven days after second spray, Fipronil 80 WG @ 50 and 40 g a.i./ha recorded lowest population of thrips (2.0 and 2.3 thrips/leaf, respectively) indicating their higher effectiveness as compared any other treatment. The next best treatment included Fipronil 5 SC @ 40 g a.i./ha with 3.1 thrips/leaf and Spinosad 45 SC @ 84.375 g a.i./ha with 4.3 thrips per leaf which differed significantly from each other. Imidacloprid 200 SL @ 45 g a.i./ha with 5.2 thrips per leaf and Standard check (Monocrotophos 36 WSC @ 360 g a.i./ha followed by Dimethoate 30 EC @ 521 g a.i./ha) with 5.5 thrips per leaf which were at par with each other were significantly inferior to above all treatments but superior to untreated check.

At ten days after second spray, Fipronil 80 WG @ 50 and 40 g a.i./ha recorded lowest population of thrips (0.6 and 0.9 thrips/leaf, respectively) indicating their higher and equal effectiveness. The latter treatment was at par with Fipronil 5 SC @ 40 g a.i./ha with 1.33 thrips per leaf. The next best treatments included Spinosad 45 SC @ 84.375 g a.i./ha, Imidacloprid 200 SL @ 45 g a.i./ha and Standard check (Monocrotophos 36 WSC @ 360 g a.i./ha followed by Dimethoate 30 EC @ 521 g a.i./ha) with 1.5, 1.8 and 1.9 thrips per leaf, respectively and were at par with each other (Table 2).

2.3 The overall efficacy of insecticides and their effect on yield and vines

All the insecticidal treatments exhibited more than 80 per cent protection against thrips. Two sprays of Fipronil 80 WG @ 50 g a.i./ha provided highest protection against thrips (95.6 and 94.5% during first and second year, respectively) over untreated check followed by Fipronil 80 WG @ 40 g a.i./ha, Fipronil 5 SC @ 40 g a.i./ha, Imidacloprid 200 SL @ 45 g a.i./ha, Spinosad 45 SC @ 84.375 g a.i./ha and Standard check (Monocrotophos 36 WSC @ 360 g a.i./ha followed by Dimethoate 30 EC @ 521 g a.i./ha) with 94.5, 90.1, 86.8, 84.6 and 82.4 and 91.8, 88.2, 86.4, 83.6 and 82.7 per cent protection during first and second year, respectively (Table 3). Similarly, Patil et al. (2017) reported that fipronil 5% SC @ 1.0 ml/l and imidacloprid 17.8% SL @ 0.3 ml/l were significantly superior with more than 87 per cent reduction of thrips damage over untreated control followed by spinosad 45% SC @ 0.25 ml/l which recorded more than 73 per cent reduction of thrips damage over untreated control. 

All the insecticidal treatments reduced more than 80 per cent of thrips population over pre-count. Two sprays of Fipronil 80 WG @ 50 g a.i./ha caused highest reduction in thrips population (96.0 and 94.8% during first and second season, respectively) over pre-count followed by Fipronil 80 WG @ 40 g a.i./ha, Fipronil 5 SC @ 40 g a.i./ha, Imidacloprid 200 SL @ 45 g a.i./ha, Spinosad 45 SC @ 84.375 g a.i./ha and Standard check (Monocrotophos 36 WSC @ 360 g a.i./ha followed by Dimethoate 30 EC @ 521 g a.i./ha) with 94.7, 91.6, 88.6, 85.4 and 83.8, and 92.2, 89.3, 85.1, 86.7 and 84.4 per cent reduction in thrips population during first and second season, respectively (Table 3). The results are in line with Niranjana (2008) who reported that Fipronil 80 WG (50 g a.i./ha) followed by spinosad 2.5 SC (84.375 g a.i./ha) and imidacloprid 17.8 EC (45 g a.i./ha) proved effective in the control of S. dorsalis in grapes. Bangosavi (2009) reported that, two sprays of spinosad @ 0.013,5 per cent were found highly effective with maximum reduction of grape thrips population.

The insecticidal treatments viz., Fipronil 80 WG @ 50 g a.i./ha and 40 g a.i./ha, Fipronil 5 SC @ 40 g a.i./ha, Imidacloprid 200 SL @ 45 g a.i./ha and Spinosad 45 SC @ 84.375 g a.i./ha recorded lowest percentage of bunches having scab symptoms (10.2, 12.1, 12.4, 12.6 and 13.5% during first season and 12.4, 14.2, 14.6, 14.8 and 15.8%, respectively during second season) and were on par with each other, while Standard check (Monocrotophos 36 WSC @ 360 g a.i./ha followed by Dimethoate 30 EC @ 521 g a.i./ha) was inferior to them with 20 and 22.4 per cent bunches having scab symptoms during first and second season, respectively (Table 3). Prema et al. (2016) reported that fipronil 80 WG at 100, 80, 60, 50 and 40 g a.i./ha reduced more than 80 per cent thrips damage to grape berries, thus recorded significantly minimum fruit damage. Bangosavi (2009) reported that minimum per cent scarred berries and higher yield were found in spinosad @ 0.013,5 per cent at harvest in grapes.

Fipronil 80 WG @ 50 g a.i./ha recorded highest yield of 10.2 and 11.6 kg/vine during first and second year, respectively and did not differ statistically from Fipronil 80 WG @ 40 g a.i./ha, Spinosad 45 SC @ 84.375 g a.i./ha, Standard check (Monocrotophos 36 WSC @ 360 g a.i./ha followed by Dimethoate 30 EC @ 521 g a.i./ha), Imidacloprid 200 SL @ 45 g a.i./ha and Fipronil 5 SC @ 40 g a.i./ha with 9.7, 9.8, 9.8, 9.6 and 9.5, and 10.9, 10.7, 10.5, 10.8 and 10.5 kg/vine, during first and second season, respectively (Table 3). Similar results were documented by Niranjana (2008) in grapes wherein he reported that the highest yield was recorded in the plots treated with fipronil 80 WG (50 g a.i. /ha) followed by spinosad 2.5 SC (84.375 g a.i./ha), fipronil 80 WG (40 g a.i./ha) and imidacloprid 17.8 EC (45 g a.i./ha). The results of present investigation are in line with Prema et al. (2016) with respect to fipronil 80 WG treatments in grapes.

Any of the insecticides tested did not show any type of phytotoxic symptoms on grape vines at the dosages tried viz., Fipronil 80 WG @ 40, 50, 100, 200 g a.i./ha, Fipronil 5 SC @ 40 g a.i./ha, Spinosad 45 SC @ 84.375 g a.i./ha, Imidacloprid 200 SL @ 45 g a.i./ha and Standard check (Monocrotophos 36 WSC @ 360 g a.i./ha followed by Dimethoate 30 EC @ 521 g a.i./ha) during both the years of study (Table 4). The results are in agreement with Niranjana (2008) who revealed that any of the insecticidal treatments did not show any type of phytotoxic symptoms on grape vines at the dosage tried i.e., Fipronil 80 WG (40 & 50 g a.i./ha), Fipronil 5 SC (40 g a.i./ha), Spinosad 2.5 SC (84.375 g a.i./ha), Imidacloprid 17.8 EC (45 g a.i./ha), Dimethoate 30 EC (300 g a.i./ha) and Monocrotophos 36 SL (500 g a.i./ha). Prema et al. (2016) observed no symptoms of phytotoxicity in the plots treated with Fipronil 80 WG at 100, 80, 60, 50 and 40 g a.i./ha. Similarly, Prema et al. (2017) did not observe any phytotoxicity symptoms in rice plots treated with Fipronil 80 WG at 40 and 50 g a.i./ha.

Author’s contributions

The author has designed and carried out the field experiments for two seasons in a well established grapevine garden. The necessary observations were recorded by author on thrips and phytotoxicity symptoms as per the protocol. The data with statistical analysis was transformed into Tables by the author. The literature pertaining to similar works was scanned by the author and the present article was prepared. The author read and approved the final manuscript.

Acknowledgments

The financial assistance by M/s Bayer Crop Science Limited, Bayer House, Central Avenue, Hiranandani Gardens, Powai, Mumbai-400 076 (M.S.) to carry out this study is acknowledged. 

References

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