During the growth of cucumber, malnutrition, improper management, or infestation with certain diseases will cause the leaves to turn yellow, affect the growth of cucumbers, and even eliminate them. According to the different symptoms of yellow leaves, vegetable farmers should determine the cause of the disease and achieve targeted prevention and treatment in order to achieve better results. 1. Nitrogen deficiency yellow leaves. The growth of the whole plant was inhibited, the leaves were small, and the upper leaves were smaller; they gradually turned yellow from lower to upper; the veins were prominent, and then extended to the whole leaves; the fruit set was small and the enlargement was slow. Control methods: Topdressing urea 5-10 kg per acre, foliar spray 0.5% -1% urea solution 2-3 times. 2. Yellow leaves lack potassium. Plant growth was not significantly inhibited. Leaf margins were slightly yellowed in the early growth period and then expanded to veins; chlorosis and necrosis of the leaf margins were observed in the mid-to-late growth stages. Occasionally, the leaves had chlorosis to necrotic spots. The melons were short and inflated poorly. Control methods: Topdressing 5-7.5 kg of potassium sulfate per acre and spraying 2-3 times of 0.2%-0.3% potassium dihydrogen phosphate solution on the foliage. 3. calcium deficiency yellow leaves. The point of growth was withered, and the upper leaves near the growth point were small, and the leaf margins were withered. The leaf shape was mushroom-like or parachute-like. The veins between the veins yellowed and the leaves became smaller; the roots were poorly developed and few were melons. Control methods: Spray 0.3% calcium chloride solution on the foliage, spray once every 3-4 days, and spray 3-4 times continuously. 4. Mg deficiency yellow leaves. After cucumber plants had 16 leaves, they were susceptible to disease. The growth of the entire plant was not significantly inhibited. The veins turned green and yellow, the margins were green, or there were green spots and no curls. Control methods: Spray 0.8%-1% magnesium sulfate solution on the leaves, spray once every 7-10 days, spray 2-3 times continuously. 5. Injury yellow leaves. The yellow leaves caused by poor root or root injury are the main reasons for the yellow leaves of the cucumber. The yellow leaves are mainly watered and fertilized with excessive roots, or they are caused by the roots of the roots caused by the cloudy days after watering. The main symptom is the general yellowing of the plant leaves, especially the top leaves are small and grow slowly, with severe wilting. Control methods: foliar spray of multi-element foliar fertilizer plus 600 times cytokinin; irrigation rooting seedling agent or chitin, etc., to promote root growth, prevent leaf senescence, and promote leaf greening. 6. Cucumber salt damage. The cucumber plants are thin, the leaves become smaller, the internodes become longer, the edges of the leaves turn chlorogenic, and then the Phnom Penh leaves are formed, sometimes accompanied by sharp-edged melons. Prevention and control methods: Prevention is the main method, and the most fundamental method for preventing salt accumulation in soil is to adhere to the application of organic fertilizers, apply chemical fertilizers scientifically and rationally, and prohibit excessive application. 7. Downy yellow leaf. Downy mildew is a disease that occurs during the growing period of cucumber and is a serious hazard. At the onset of the seedling stage, the leaves turned green and yellow and finally died. The onset of adult leaves began to appear as water-stained yellow round spots on the back of the leaves, especially in the morning, and gradually developed into yellow-brown polygonal lesions. Under high temperature conditions, the back surface of the lesion showed a brownish brown mold layer. In severe cases, the lesion was patchy, and the whole leaf was yellow-brown. The leaf margin curled and withered. Control methods: Use 58% of D. MnZn WP 500 times, 72% WP wettable powder 600 times, 75% chlorothalonil wettable powder or 50% carbendazim wettable powder 600 times. Foliar spraying, spraying once every 7 days, generally 3-4 times. 8. Cucumber root knot nematode disease yellow leaves. Root-knot nematode disease mainly damages the lateral roots and fibrous roots of cucumber, and root-like or lateral roots produce nodules of varying sizes, light yellow to yellow-brown. The symptoms of the mildly diseased aboveground parts were not obvious. When the disease was severe, the plants were obviously dwarfed. The melons were small and small, and the leaves were chlorotic yellow. On sunny days, the above-ground parts of the plants showed wilting or yellowing, and finally the plants died. Dissecting the root knot, there are many slender, mottled nematodes parasitizing the diseased tissue. Control methods: 1.8% avermectin emulsifiable concentrate 1500 times or 70% phoxim EC 1000 times, irrigate 7-10 days, and 2-3 times per irrigation, 300 -500 ml. Puyang Linshi Medical Supplies Co., Ltd. , https://www.linshimedicals.com