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ABSTRACT

Watermelon is one of the food crops with the highest demand during summer among the masses. The health benefits and cooling nature of the watermelon always make it a valuable commodity which also is remunerative for the farmers who cultivate watermelon. A plethora of challenges and opportunities await the farmers who take up watermelon cultivation, as it is affected by various pests and diseases. Various chemicals are employed in the cultivation of watermelon in addition to a few harmful adulterants for improving the marketability of watermelon. In long run, such chemicals could lead to health risks in consumers. These challenges should be addressed and awareness must be created among farmers and consumers about the I`ll effects of

Keywords: post-harvest, value addition, insect pests, insecticide residues, adulterants, dyes, export.

Watermelon, Citrullus lanatus, is a vining annual plant and it belongs to the cucurbit family. It is a native of Africa. It is called by names such as the “fruit of the 22nd century” and “common man’s fruit”. It is a crop grown by farmers almost all throughout the globe wherever favourable climatic and temperature conditions exist.  It is an important dry season crop grown in India for its juicy fruits. The health benefits of the watermelon also make it a preferred choice among the consumers. China is the largest producer of watermelon in the world, followed by Turkey, Iran, Brazil and Egypt, while India occupies 25th position world-wide. In India, watermelon is mostly grown as a river-bed crop in the states of Uttar Pradesh with more than 25% of the production in the country, followed by Andhra Pradesh, Karnataka, West Bengal, and Orissa. Like almost all the cultivated crops, watermelon cultivation is also faced with a series of threats. One among the threats is insect pests which attack the watermelon crop in the field. Insect pests qualitatively and quantitatively affect the watermelon fruit production, which is otherwise a highly productive and remunerative crop. Therefore, farmers employ a multitude of pest management strategies to counteract the attack of the pests. Chemical insecticides play a major role in combating the insect pests affecting watermelon crop. Since they offer quick results, farmers tend to depend more on chemical control rather than other methods of pest control, thereby increasing the pressure on chemical control. Since watermelon crop is also prone to a lot of viral diseases, killing the vector insects which carry the viruses becomes a necessity, for which more insecticides are used.  Over usage of chemical insecticides than the recommended dose leads to a few ill effects, one among which is pesticide residues on the crop. Pesticide residues reduce the marketability, deprive the crop of its health benefits and may lead to health hazards in the consumer. So, it is crucial for the farmers to understand the importance of pesticide usage and the downside of the overuse of chemical insecticides.

Health benefits of watermelon

Besides being a delicious fruit, watermelon also provides the following benefits to humankind. For starters, watermelon keeps the body hydrated since most of the watermelon pulp is composed of water. Watermelon contains low calories, but various nutrients including Vitamin C, Vitamin A and Potassium. Researches also show that watermelon has high lycopene content (45.32 %) and other compounds which reduce the risk of cancer. Additionally, watermelon is also good for the heart, thus reducing the risk of heart diseases. Watermelon also helps to relieve the soreness in muscles, prevent macular degeneration, lower inflammation and oxidative stress. It also improves digestion, and is believed to provide clear skin and strengthen the hair. In short, watermelon too can keep the doctor away.

 Cultivation of watermelon

Watermelon prefers a sandy loam soil with a pH range of 6.5-7.5. The fertile alluvial along the river beds are also ideal for growing watermelons. Warm temperature is ideal for watermelon cultivation. But they can also be grown in cooler conditions through choosing the correct time of planting to ensure that the frost damage can be avoided. The best season for sowing the watermelon is December month so that the fruits can be ready for the summer season. Based on the duration of the variety, one or two crops can be raised in the growing season. Extreme summers as well as the wet condition due to showers are not preferred by the crop and they may lead to reduced production as well as quality. Usually, 3-4 kg of watermelon seeds is used for planting in one hectare of land.

 Watermelon pests, pesticide usage pattern and insecticide resistance

The most notorious ones among the invertebrate pest complex associated with the watermelon crop are red pumpkin beetle, melon fruit fly, leaf eating caterpillar, serpentine leaf miner, the sucking pest complex consisting of whitefly, aphid, thrips and the red spider mite Tetranychus urticae. The only insecticide recommended by the CIBRC (Central Insecticide Board and Registration Committee) in the crop is the thiourea compound, Diafenthiuron 50 % WP, which selectively controls sucking pests and mites which often are resistant to organophosphorous and pyrethroid insecticides. It affects the mitochondria of the cells and thus inhibits the respiratory functioning of the insects. Diafenthiuron is available in various trade names like Pegasus, Pager, Derby, and Solo.

The most devastating among the sucking pest complex of watermelon is the thrips. Thrips in addition to directly causing economic loss by feeding on the sap, also act as the transmitting agent of an important virus infecting the crop – watermelon bud necrosis (WBN) virus which is basically the watermelon strain of tomato spotted wilt (tospo) virus (TSWV-W). The disease causes symptoms of leaf crinkling, mottling, yellowing, necrotic streaks on vines and dies back of buds severely affecting the productivity of the crop. The yield losses due to this viral disease range up to 80-90%. Application of acephate 75 SP or dimethoate 30 EC at 2ml/l of water in combination with neem oil at 10 days interval from germination to fruiting stage is recommended for reducing the thrips population. Foliar application of imidacloprid 70% WG @ 35 ml//ha is recommended for controlling aphids which transmits another viral disease - watermelon mosaic.

In the first quarter of 2021, it was reported that watermelon and cow pea fields in Goa were devastated by the melon moth, Diaphinia indica. The irrational spraying of chemical insecticides like dimethoate, an organophosphorous compound and deltamethrin & cypermethrin, members of synthetic pyrethroids, was found to be the reason that aggravated the pest problem. Instead of bringing down the pest population, the unscientific use of the insecticides imparted resistance to the insect causing a widespread attack. Limiting the use of these insecticides and switching to eco-friendly methods like use of pheromone traps against fruit flies and sticky traps for sucking pests, significantly improved the quality and yield in the watermelon fields.

 Pesticide residues and adulterants in watermelon

The pesticide risk assessment in a daily diet is almost an impossible task given an average person consumes multiple food products in a day which are exposed to different pesticides at different levels. As the farmers sometimes tend to depend more on pesticides and use them at dosage higher than that recommended to obtain complete control of insect pests, the risk of residual pesticides on the marketed produce becomes higher. Prolonged intake of residual pesticides along with the fruit might result in risk of accumulation of toxic pesticides in the body leading to health issues. Various studies show that about 20% of Indian food products contain pesticide residues above the tolerance level compared to only 2% globally. No detectable residues are found in 49% Indian food products compared to 80% globally. Even artificial-ripeners like calcium carbide which are used to hasten the ripening process of the fruits are used in plenty in the country. The matter of fact is that this product is banned for use in India and is still being ludicrously abused in several fruits including watermelon. This has proven to have had serious ill-effects on the population, including kidney damage.

In addition, a variety of dyeing substances are injected into the watermelon fruit as consumers prefer ripe and red fruits. These chemicals make the fruit appear reddish in colour so that it seems riper for increased visual appeal and to assure the buyers that the fruit has reached maturity. Few of the dyeing substances used commonly are lead chromate, methanol yellow, Sudan red, etc. These substances can create various negative impacts on the health of the consumers, like damage to brain cells leading to blindness, digestive problems, food poisoning or sometimes even cancer. Therefore, residue analysis should be done for rapid quantification and identification of pesticide residues and adulterant chemicals, if any, on the watermelon field and market samples.

A recent survey conducted in the Haryana-Delhi region claimed that the proportion of farmers who adopted practices to minimize residual effects was around 48 per cent, which can be considered a rather higher value. Practices such as use of pheromone traps, spraying pesticides based on pest: defender ratio was adopted in a limited scale only, although use of artificial sweeteners to improve the taste of watermelon and muskmelon was rarely undertaken. But the major reason that seems to contribute towards the residue levels in the market samples might be due to non-adoption of pre-harvest intervals (PHIs) – fruits are harvested right after the pesticide spray and transported to the market. Only around one-fifth of the farmers adopted PHIs.

 Challenges and possibilities in watermelon production and trade

In addition to a myriad of associated pests and diseases, there is a significant lack of systematic studies on cost-effective cultivation practices for watermelon. Other factors like perishability of the produce, inadequacy in transportation and involvement of middlemen/ commission agents has brought down the potential income of the local growers.  But the recent entry of yellow-fleshed watermelon into the picture has given hope to these farmers to take advantage of the novelty of the product in order to increase their income.

Yellow fleshed variant is likely to fetch a higher price in the market. Bayer in 2021 had introduced the first-ever yellow fleshed variety into the market namely ‘Yellow Gold 48,’ under its Seminis brand of vegetable seeds. It is claimed to have been developed from a superior germplasm and offers added qualitative advantages like distinct sweet flavour and has thicker rind compared to the usual varieties, enabling longer shelf life and reducing potential losses from damage during transportation from farm to markets. Countries like UAE, Maldives, Nepal, Netherlands and Qatar are export destinations for watermelon from India. Among these nations, exports to UAE accounts for three-fourth of the total watermelon export. Post-harvest by-products including preserved peel of watermelon are highly valued in these countries.

Conclusion

 

It is evident that watermelon is a fruit which provides numerous health benefits. With adequate planning, watermelon cultivation can turn out to be remunerative for the farmers during summer due to its `beat-the-heat` nature, high productivity and short cropping period which enables the farmers to even harvest a second crop in the same season. It also has a significant demand in the global market, which can be exploited to bring in a lot of foreign currency to the country. Therefore, it becomes the need of the hour to maintain the pesticide residue levels under the permissible levels so as to meet international trading standards. Farmers must be educated on proper and precise use of pesticides, pre-harvest intervals and about the maximum residue limits permissible for each pesticide employed in watermelon cultivation. It must be ensured by rigorous analysis of pesticide residue levels in the watermelon fruits. Enforcement of strict laws should be done by the authority to ascertain that only a harmless and healthy produce reaches the consumer. 

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Watermelon Cultivation and Trade – An Overview, Food and Scientific Reports.pdf