Performance of spinetoram SC against thrips and leaf miners infesting watermelon crop

Introduction

Watermelon (Citrullus lanatus) (Thunb.) is a vining annual plant belongs to the family Cucurbitaceae, and grown for fleshy fruits in the tropics. The fruit is dominant during summer season especially due to its high-water content and delicious taste. It is newly introduced cash crop having good source of vitamins A and C, antioxidants, and essential minerals, contributing to its nutritional and economic value (Otutu et al., 2015) [8] . It has the highest iron concentration of any cucurbitaceous crop. Because watermelon rinds include fiber, minerals, phenolic compounds, and essential amino acids like citrulline, they also provide a lot of health benefits. The occurrence of high arginine content in the seeds of watermelon adds its medicinal benefits (Kaul, 2011) [6] . In India, watermelon is grown on an area of 127 lakh hectares with an annual production of 3632 lakh tones in the year 2023-24. It is grown particularly as a major river-bed crop in states like Uttar Pradesh, Karnataka, West Bengal, Madhya Pradesh, and Rajasthan (Chadha, 2013) [3] . In Chhattisgarh, it covered an area of 3.22 lakh hactares and produced 37.75 lakh tones in 2023-24 (Anonymous, 2023) [2] . Despite its increasing popularity, a number of insect pests provide serious problems for watermelon crops, attacking the plants at all stages, from seedlings to fruit maturation. These pests affect farmers' livelihoods by lowering produce quality and causing significant yield losses. The major insect pests that pose a threat to successful watermelon cultivation include leaf miners (Liriomyza trifolii), thrips (Thrips palmi), cucurbit fruit fly (Bactrocera cucurbitae), red pumpkin beetle (Raphidopalpa foveicollis), aphid (Aphis gossypii), red spider mite (Tetranychus urticae) and whitefly (Bemisia tabaci).

Among these pests, Liriomyza trifolii, is an important polyphagous insect especially in the early phases of growth. By feeding on the mesophyll tissues while preserving the epidermis, this pest forms serpentine mines on the upper surfaces of leaves (Chandler and Thomas, 1983) [4] . According to research, infestations of leaf miners can harm watermelon crops by up to 37% (Patnaik, 2000) [9] , significantly lowering yields. Another common and damaging insect in watermelon farming is the melon thrip (Thrips palmi). These insects harm plants directly by eating on their tissues and indirectly by serving as carriers of plant viruses including groundnut bud necrosis and watermelon silvery mottle virus. Thrips can result in yield losses of 60% to 100%, depending on the hybrid or watermelon variety and when it is sown (Krupashankar, 1998) [7] . The total productivity and financial sustainability of watermelon cultivation may be significantly impacted by this degree of damage. Hence the present study was conducted to evaluate the bioefficacy of Spinetoram 11.7% SC against thrips and leaf miner in watermelon.

Materials and Methods

The present experiment was conducted at Sant Vinobhabhave College of Agriculture and Research Station, Marra, Patan (Durg) during the period of Rabi 2023-24 to evaluate the bioefficacy of Spinetoram 11.7% w/w SC (12%w/v) against thrips and leaf miner in watermelon. The experiments was laid out in completely randomized block design (RBD) with six treatments including control and replicated four times. The Nadiyarani crop variety was grown in a plot measuring 50 m 2 (10 m by 5 m) with a spacing of 120*60 cm (P*R). The watermelon crop was raised according to the recommended agronomical practices. Two rounds of spraying were done during the crop season by using 500 litres of spray solution per hectare with high volume knapsack sprayer fitted with hollow cone nozzle.

Methods of Observation Leaf miner, Liriomyza trifolii (Burgess):

The abundance of watermelon leaf miner on plants was monitored by selecting 15 twigs per plant with fresh leaves. From selected twigs the damaged leaves with leaf miner galleries and number of total leaves on those branches were counted. Pre-treatment count of leaf miner was recorded a day before the insecticides applications. Using the data, the percent leaf miner incidence at 7 DAA, 14 DAA after each application was calculated.

Thrips, Thrips palmi (Karny):

The thrips observations started from flower bud initiation. Pre-treatment count (0 DAA) on number of thrips (nymphs and adults) were taken one day before imposing treatments. Numbers of thrips per twig were counted. A twig of 15 cm with tender leaves on white piece of A4 size card paper were tapped 5 times arbitrarily and the same process was repeated for 20 twigs per plot to take the average count of thrips at 7, 10, and 14 days after first application and second application. The collected thrips were returned to the plant as much as possible. The data obtained were subjected to ANOVA for a randomized block design (RBD) with appropriate statistical transformation and further, the percent reduction of pest population in respective treatments over control was computed by using the formula (Abbott's 1925) [1] .

Percent reduction = C-T/C x 100

Where, T = Insect population reduction in treated plot. C = Insect population reduction in control plot The watermelon yield from each plot was pooled and expressed as tonnes ha -1 .

Results and Discussion a) Bioefficacy of insecticides against leaf miner

The observations on pre treatment infestation by leaf miners among all the treatments were found to be non-significant (Table 2). The data on the mean percent leaf infestation (7 & 10 days) after first spray showed that Liriomyza trifolii infestation level varied among the various insecticidal treatments compared to untreated control (44.55%). Spinetoram 11.7% SC @63 g a.i./ha (T 3 ) recorded the lowest per cent infestation (25.03%) which was at par with Spinetoram 11.7% SC @54 g a.i./ha (T 2 ) with 26.04%. Spinetoram 11.7% SC @45 g a.i./ha (T 1 ) with 31.03% and Cyantraniliprole 10.26% OD @90 g a.i./ha (T 4 ) (30.69%) were next in terms of effectiveness while T 5 i.e. Fipronil 05% SC @50 g a.i./ha (35.64%) being the least effective treatment. The data on the mean percent leaf infestation (7 & 10 days) after second spray revealed that all the insecticidal treatments significantly reduced the percentage of leaf infestation when compared to the control (22.59%). Among the different treatments, the lowest percent infestation of 13.30% was recorded in T 3 which is Spinetoram 11.7% SC @63 g a.i./ha followed by Spinetoram 11.7% SC @54 g a.i./ha (13.51%) and Spinetoram 11.7% SC @45 g a.i./ha (15.34%). Fipronil 05% SC @50 g a.i./ha (19.45%) was least effective than Cyantraniliprole 10.26% OD @90 g a.i./ha (16.00%). The overall mean percentage of leaf infestation was recorded minimum in T 3 i.e. Spinetoram 11.7% SC @63 g a.i./ha with 19.16% which was most effective among all the treatments and was at par with Spinetoram 11.7% SC @54 g a.i./ha (T 2 ) with 19.77%. Spinetoram 11.7% SC @45 g a.i./ha (23.18%) and the market standard Cyantraniliprole 10.26% OD @90 g a.i./ha (23.34%) were moderately effective. The least effective treatment with maximum percentage of leaf infestation was recorded in T 5 which is Fipronil 05% SC @50 g a.i./ha (27.54%). Present results are in conformity with those of Kkadan et al.,(2020) who assessed the Spinetoram for control of lepidopteran in the field and nursery. Hamza et al., (2023) [5] who reported after 7 DOA, Spinetoram (76.98%) demonstrated the highest insecticidal effectiveness, as measured by the percentage reduction in leaf miner infestation.

b) Bioefficacy of insecticides against thrips

The population of thrips ranged from 8.18 to 12.68 per leaf at a day before spray indicating uniform distribution throughout the experimental field and there was no significant difference between the treatments and the results obtained are presented in Table 3. The minimum population of nymph and adults per leaf at 7 and 10 days after the first spray of insecticide was recorded in the plot T 3 , treated with Spinetoram 11.7% SC @63 g a.i./ha (3.97 & 3.46 thrips/leaf) and Spinetoram 11.7% SC @54 g a.i./ha (T 2 ) (4.02 & 3.56 thrips/leaf) which was statically superior over the other treatments such as Spinetoram 11.7% SC @45 g a.i./ha (T 1 ) (4.20 & 3.90 thrips/leaf) and the market standards like Cyantraniliprole 10.26% OD @90 g a.i./ha (T 4 ) (5.66 and 6.66 thrips/leaf) and Fipronil 5%SC @50 g a.i./ha (T 5 ) (5.81 and 7.04 thrips/leaf). The second spray, applied 14 days after the first spray, showed consistent efficacy trends. The post treatment results at 7 and 10 days after second application revealed that Spinetoram 11.7% SC @63 g a.i./ha was again the most effective in reducing the population to (0.00 and 0.54 thrips/leaf) followed by Spinetoram 11.7% SC @54 g a.i./ha (T 2 ) (0.00 & 0.66 thrips/leaf). The untreated control maintained the highest population at 16.46 & 17.18 thrips/leaf while, Fipronil 5%SC @50 g a.i./ha was least effective. The overall reduction in thrips population compared to the control ranged from 91.14% to 75.15%. Spinetoram 11.7% SC @63 g a.i./ha achieved a 91.14% reduction, followed by Spinetoram 11.7% SC @54 g a.i./ha at 90.87%. Spinetoram 11.7% SC @45 g a.i./ha and Cyantraniliprole 10.26% OD @90 g a.i./ha showed notable reduction of 87.71% and 76.92%, respectively. Fipronil 5%SC @50 g a.i./ha was least effective with reduction of 75.15%. The present findings are in confirmation with Seal (2011) [11] who mentioned that spinosad at 0.13 lb a.i. per acre and spinetoram at 0.13 lb a.i. per acre, provide a considerable degree (>90%) of control for the management of T. palmi on watermelon. According to Tan et al., (2021) [12] , the populations of T. palmi showed a resistance ratio (RR) of 1.69 against spinetoram, showing low resistance to this pesticide which matches with the current finding.

Yield: After the harvest of the crop, yield data was recorded for each plot and was converted to tonnes per hectare (Table 4). It was observed that, the highest yield of Watermelon was recorded in T 3 which is Spinetoram 11.7% SC @63 g a.i./ha (20.15 t/ha) which was at par with T 2 i.e Spinetoram 11.7% SC @54 g a.i./ha (19.93 t/ha) and significantly superior than Spinetoram 11.7% SC @45 g a.i./ha (T 1 ) (16.15 t/ha) and the market standards i.e Cyantraniliprole 10.26% OD @90 g a.i./ha (T 4 )(15.63 t/ha) and Fipronil 05% SC @50 g a.i./ha (T 5 ) (12.69 t/ha). Similar results was also reported by Sarkar et al., (2024) [10] who mentioned highest yield of 78.89 tonnes/ha was recorded in the T 1 which was treated by spinetoram 11.7% SC @ 0.5 ml/L. Conclusion-In Rabi 2023-24, treatment Spinetoram 11.7% SC @63 g a.i./ha (T 3 ) recorded significantly superior control over thrips and leaf miners which was at par with Spinetoram 11.7% SC @54 g a.i./ha (T 2 ). Treatment Spinetoram 11.7% SC @63 g a.i./ha (T 3 ) also recorded highest yield. Hence, it can be concluded that this insecticide is highly effective in controlling both the pest and can be recommended to the watermelon growing farmers.

References

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