How to prevent and control the "yellow ring leaf" of cucumber in greenhouse

The "yellow ring leaf" is common in cucumber overwintering cultivation, which seriously affects the yield and economic benefit. This phenomenon is not caused by infectious diseases, but generally belongs to physiological diseases. First, the symptoms showed that there were more occurrence in the middle and lower leaves of cucumber. At the beginning, the edge of the leaf is yellow, and then develops to the inside of the leaf along the edge of the leaf. The phenomenon of turning green is 2-3 cm wide, and then it is yellowish green, so it is called "yellow ring leaf". When the occurrence is serious, the yellow ring scorches and the leaves die. 2. occurrence conditions and regularity the disease is caused by lack of potassium in plants. It occurs seriously when the temperature is low. This is due to the low soil temperature and the decrease of the activity of microorganisms in the soil, resulting in the imbalance of the ratio of ammonium nitrogen to nitrate nitrogen and inhibiting the absorption of potassium. Therefore, although there is no potassium deficiency in the soil, the cucumber still shows the symptom of potassium deficiency. When the soil is too sandy, the application of organic fertilizer is insufficient, and the lack of potassium fertilizer occurs more seriously. Cucumber "yellow ring leaves" can also occur when the ground temperature is too low in the greenhouse. Third, prevention and control methods (1) to improve the ground temperature in the solar greenhouse. Improve the structure of the solar greenhouse, such as thickening the wall, digging cold ditches, increasing the height of the greenhouse, increasing the incident angle of sunlight, increasing the incidence rate of sunlight, double covering with plastic film and grass with good thermal insulation performance, and hanging a reflective screen on the north side of the greenhouse. (2) increase the application of organic fertilizer and appropriate amount of ammonium nitrogen fertilizer. When applying chemical fertilizer, pay attention to the reasonable collocation of nitrogen, phosphorus and potassium. (3) during the cold winter growth period, spraying Shuofeng 481 solution once could promote photosynthesis and root growth and development. (4) when the temperature is low, 0.2% potassium dihydrogen phosphate solution is sprayed every 3 to 5 days to supplement the potassium supply of the plant. At the same time, enhance the cold resistance of the plant.