Long spots on melons can be caused by several factors. First, delayed ventilation after covering the greenhouse can lead to high temperature and humidity. Once the cover is removed, water droplets form on the surface of the melon as the temperature rises, creating an environment where green spots are more likely to develop due to poor air circulation under hot conditions. Second, over-crowding in planting can also contribute to this issue. Some farmers increase planting density to boost early yields, but this leads to poor air and light penetration, resulting in green spots on the fruit. Third, improper timing of pesticide application, especially during high temperatures, can cause damage to the melon surface, leading to green spots. Finally, using a high concentration of pesticides can directly harm the melon's surface, causing green discoloration.
To prevent long spots, proper ventilation is essential. After removing the greenhouse cover in the morning, start by opening the air vents slightly, avoiding a sudden drop in temperature. Gradually increase the venting as the internal temperature rises, allowing moisture on the melon surface to evaporate. The ideal temperature inside the greenhouse should be maintained between 28°C and 30°C. Even on cloudy days, short periods of ventilation are necessary to avoid moisture buildup.
Proper planting density is also important. It’s recommended to keep the planting density at around 2,500 to 2,800 plants per acre. Grafted melons should be planted at the lower end of this range, while non-grafted ones can be slightly denser. This ensures better air circulation and light exposure, reducing the risk of green spots.
When applying pesticides, choose the right time. It’s best to spray in the early morning, between 9 and 10 a.m., or in the late afternoon after 2 p.m. Avoid applying pesticides when there are still water droplets on the melon surface, as this can lead to chemical burns and green spots. Lastly, always follow the recommended concentration for the pesticide. Using too low a concentration may not be effective, while too high a concentration can cause damage to the fruit. Always prepare the solution according to the manufacturer’s instructions to ensure both safety and effectiveness.
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