Thrips causing rough leaves and misshapen watermelon fruit – what to do?
Among vegetable crops such as cucumber, eggplant, wax gourd and bitter melon…, watermelon is one of the crops most heavily damaged by thrips. Thrips thrive in hot, dry weather, are highly resistant to pesticides and quickly adapt to them. Therefore, for effective control, farmers need to apply several measures at the same time to protect their crops.
Thrips: common in the hot, sunny season
In the last Tet watermelon season, many farmers in Bình Tân were disappointed because thrips attacked their watermelons, so although Tet prices were good, yields were low.
Ms Nguyễn Thị Hồng (Tân Hưng commune, Bình Tân) said: "I grew 4 công of watermelon, but this year the crop failed because thrips attacked so fast I couldn't treat them in time; the field became weak and twisted, fruit was small, and yield fell 30- 40% compared with last year."
Some farmers shared that adult and larval thrips are very small, whitish-yellow, live concentrated in young shoots or on the undersides of young leaves, and suck sap so that young leaves develop small pale-yellow spots and curl. In some watermelon fields, high thrips density causes flower drop, no fruit set or small fruit, yellow and withered leaves, and stunted, weak plants. Because thrips concentrate mainly in young shoots, under heavy damage the shoots grow upright, become stiff and point upwards – known as "lion-head" melons.
According to the authorities, thrips are a pest that has devastated some melon-growing areas. Thrips are also vectors of mosaic disease in melons. Because they are quite small and usually hide on the undersides of shoot leaves, beneath the hairs on the leaf underside, thrips are very hard to detect without careful observation. On young leaves, while feeding, young thrips excrete a very characteristic green frass, but at the adult stage their frass is blackish.
Mr Dương Ái Đạo, Deputy Head of the Agriculture and Rural Development Office of Vũng Liêm district, said: Thrips thrive in hot, dry weather, are highly resistant to pesticides and quickly adapt to them. Under suitable conditions, thrips develop very quickly, greatly affecting the growth and yield of melons and many other vegetables and crops.
How to control thrips on watermelon
To manage thrips on watermelon in particular and vegetables in general, Mr Dương Ái Đạo recommends: clear residue from the previous season, fertilise and water adequately so melons grow well, choose healthy, disease-free varieties, and protect natural enemies such as yellow ants and wasps.
In addition, when thrips density is high, a chemical product can be used, such as: Pilaravia 155SC
Rate: 0.12%, equivalent to 24ml per 20L tank
Water volume: 600 - 800 L/ha
Spray preventively or curatively when the orchard is attacked by mealybugs at a low level or 5-7 per vine
Interval between 2 sprays ≤ 7 days, or a 3rd spray can be added if mealybug pressure is high
Advisory contact: +84 86 210 5050 (Free)
