During the growth of cucumber, if malnutrition, improper management, or infestation with unfavorable weather and certain diseases, often cause yellowing of the leaves, affecting the growth of the cucumber, or even the harvest. There are three main reasons for the yellowing of cucumber leaves, which are summarized as follows:
1 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. In the middle and lower parts of the old yellow leaves, the missing elements are mostly easily reusable elements in the plant body, such as nitrogen, potassium, magnesium and zinc. 1 The growth of the entire plant was inhibited, and the older leaves were greenish and lacking nitrogen. The control strategy is to spray the leaves with 0.5%-1% urea solution 2-3 times. 2 The whole plant growth was not significantly inhibited. The veins turned green and yellow, and the leaf margins were green, or there were green spots and no curls. It was magnesium deficiency. The control strategy is to spray 1%-2% magnesium sulfate solution on the leaves. 3 No significant inhibition of plant growth, chlorosis and even necrosis of the leaf margin, sometimes there are chlorosis to necrotic spots on the leaf, potassium deficiency. The prevention and control measures are foliar application of 0.3%-0.5% potassium dihydrogen phosphate solution 2-3 times. 4 No significant inhibition of plant growth, the entire leaf has chlorosis to necrotic spots or striations, 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 the plant body, such as calcium and iron. 1 The growing point was dead, the leaves lacked green and shrunk to necrosis; the roots were poorly developed, and few were melons, which was calcium deficiency. Control measures Foliar spray 0.3% calcium chloride solution twice a week. 2 The growing point does not die, the leaf color is light green, and the small stems are short of sulfur. The prevention and control measures are foliar spraying with 1% potassium sulfate solution. 3 The growing point does not die, the leaves are yellowish-white and iron-deficient. The prevention and control measures are foliar spraying of 0.5% iron sulfate solution.
2 Downy yellow leaves
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. In the adult stage, the 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 which were yellow-green. Under high humidity conditions, the lesions grow on the back of the brown-brown mildew layer. In severe cases, the lesions become patches. The whole leaf is yellow-brown and the leaf margins are curled and withered. The prevention and control measures are foliar spraying with 50% WP (wettable powder, the same below), 75% chlorothalonil WP, and 50% WP WP 600 times, once every 7 days. , spray 3-4 times.
3 Blight 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 yellowish 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. Rhizome disease has an amber gel, and when the humidity is high, white or pink molds appear on the surface. When you break off the stem or main root, you can see the interior turning brown. The prevention and control strategy is to use 50% carbendazim WP 500 times, or thiophanate-methyl 50% WP500 times to irrigate the roots, each strain is not less than 250ml, 5-6 days irrigation once, with irrigation 2-3 times.
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