The temperature is too high, the soil moisture is too high, etc.. The temperature in the morning is low, and the temperature rises at noon, the temperature change leads to the leaves of the melon in the middle of the day to become sticky soft, excessive high temperature leads to the loss of water and wilting of the plant, the melon needs the right soil moisture to maintain normal growth, if the melon is subjected to over-watering or soil drainage is poor, it will lead to damage to the root system, can not absorb enough water, resulting in the phenomenon of sticky soft leaves, and so on.