During the growth of cucumber, if malnutrition, improper management, or encounter with bad weather and certain diseases, it will cause the leaves to turn yellow, affect the growth of cucumber, and even harvest. There are mainly three types of yellowing of cucumber leaves:
Lack of yellow leaves. The lack of yellow leaves is divided into middle and lower old leaves first yellow and middle and upper young leaves first yellow. The middle and lower parts of the old leaves are first yellow, and the missing elements are mostly elements easily reused in the plant body, such as nitrogen, potassium, magnesium and zinc. 1. The whole plant growth was resisted, and the older leaves were greener than the entire leaf, which was nitrogen deficiency. Prevention and control measures are foliar spray 0.5% ~ 1% urea solution 2 ~ 3 times. 2. The whole plant growth did not significantly resist the loss of greenish yellowing of the veins, yellowing of the veins between leaves and veins, green edges of the leaves, or residual green spots, no curls, and magnesium deficiency. Prevention and control measures are foliar spray 1% ~ 2% magnesium sulfate solution. 3. The plant growth was not significantly inhibited, the leaf margin was chlorotic and even necrotic, and sometimes the leaves also lost chlorosis to necrotic spots, which were potassium deficiency. Prevention and control measures are foliar spray 0.3% ~ 0.5% potassium dihydrogen phosphate solution 2 ~ 3 times. 4. There was no obvious resistance to plant growth. The entire leaf had chlorosis to necrotic spots or striations and was zinc deficiency. The control strategy is foliar spray of 0.2% zinc sulfate solution. The middle and upper young leaves are yellow, and the missing elements are mostly elements that are not easily reusable in plants, such as calcium, sulfur, and iron.
Yellow downy leaf. Downy mildew is a disease that occurs during the growing period of cucumber and is a serious disease. At the onset of the seedling stage, the leaves turned green and yellow and finally died. Onset of adult leaves began to appear yellow spots on the back of the leaves, especially in the morning, gradually developed into yellow-brown polygonal lesions, the edges of lesions yellow-green. Under high temperature conditions, the lesions on the back of the lesions are grayish-brown moldy. In severe cases, the lesions are divided into patches. The whole leaf is yellow-brown and the leaf margins are curled and withered. The prevention and control measures are foliar spraying with Rhizoctonia, Manganese and Zinc 58% wettable powder 500 times or 75% chlorothalonil wettable powder, 50% lyophilized wettable powder 600 times, once every 7 days. Spray 3 to 4 times.
Wilt yellow leaves. Fusarium wilt is commonly known as "death." At the early stage of disease, some leaves wilted at noon and recovered sooner or later, and they did not recover after several days. Leaf color gradient yellow-green to yellow-brown, from bottom to top gradually extended to the whole plant. The main vines on the near ground were rotted, thinned or longitudinally cracked, gradually dry, and the whole plant died. The rhizomes have an amber gel, and when the temperature is high, white or pink molds appear on the surface. When the stems or main roots are broken, the interiors can turn brown. Prevention and control measures: Use 50% carbendazim WP 500 times solution, or thiophanate-methyl 50% WP 500 times solution, and each solution should not be less than 250 ml, and 5 to 6 days for irrigation. Even irrigation 2 or 3 times.
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