In the past few days, many cotton farmers have reflected the phenomenon of “yellow leaves†in cotton. After investigation and analysis, there are several situations as follows. 1. "Yellow reticulum" blight. Yellow veins, chlorotic turns into yellow or yellow-white veins, leaf sections remain green, showing yellow reticulate patches. It may also be partially or totally yellow. Starting from the leaf edge or tip, it generally develops from top to bottom. The development of this symptom is relatively slow, but it can be extended to the entire leaf, and finally dry off, the cotton plant died. (For the prevention and control methods, see the article "Triad Prevention and Treatment of Cotton"). 2. "Macropathy" Verticillium wilt. Vein veins are not yellow, and the veins remain green near the veins. In the early stages of the disease, the mesophyll produces irregular yellowish irregular lesions. The edge of the diseased leaf curls slightly. As the disease progresses, the color of the pale yellow patches gradually darkens, appearing yellow to brown, The edge of the leaf curls upwards, which in turn develops a palmar palpebral spot that resembles a "flower rind." It usually starts from the middle and lower leaves and the leaves do not fall off (Sun Wenjiang from Yanwotou Village, Guantao County, and Zhang Fengtu from the North Baoxu Village, Jingtong County belong to the same cotton field. The control method is the same as above). 3. Iron deficiency "yellow leaves." The veins are not yellow, and the young leaves begin to lose their green color in the intervein veins, and then completely lose their greenness, manifesting themselves as "chlore deficiency syndrome" or "chlorosis syndrome." Sometimes, the entire leaf appears yellowish-white at first. Many new leaves are chlorotic and old leaves can still remain green. The stems are short and weak, and the content of phosphorus, zinc, manganese and copper in the soil is too low. The soil has high viscosity and high water saturation. The use of nitrate nitrogen fertilizer will increase the iron deficiency. Responsive measures: Can be sprayed with 0.2% ferrous sulfate solution, 2 times in a row (preparation with 0.1% -0.2% vinegar to make the water acidified). Note that the prepared solution should be light green without precipitation, and if the solution turns auburn or produces a large amount of auburn precipitates, it indicates that it has been oxidized and has no effect. It is advisable to use products such as complex iron and chelated iron available on the local market. 4. Potassium deficiency "yellow leaves." The veins are not yellow, and the veins between leaves and veins are yellowish. It generally occurs from the leaf margin to the center and from the tip to the leaf base. Generally occurs from the lower leaves first, and the upper part develops; when it is particularly severe, it can be expressed on the middle and upper leaves, and the veins are chlorogenic and yellowish-white. There are obvious brown and red-brown spots between the veins (tip size ), followed by brown, red, orange-red necrosis, and can develop into the whole leaf. Sometimes the leaves are shriveled, brittle, and scorched, and the leaf edges curl upwards or downwards (the performance symptoms of Song Wuqin cotton field in Hezhai Village, Guantao County are potassium deficiency and iron deficiency). 5. "yellow leaf" red stem blight. The veins are not yellow, and the mesophyll tissue is chlorotic. At the onset of disease, the edges of leaves are slightly yellowish. From top to bottom, from outside to inside. After development, the leaves can turn from yellow to purple-red, and the leaves are thickened, shrunk, and brittle. (Note: This disease is related to low potassium in the soil, but it is different from a single potassium deficiency disease). Responsive measures: Spray 600 times of 35% Phosphorus Potassium + 1% urea solution on the leaves and make up the soil to recover Potassium fertilizer in time, rationalize the adjustment, and reasonably drain irrigation. In addition, there is a lack of boron (yellow veins, yellowing of the edges, upper young leaves, leaf curling), lack of manganese (vein veins are not yellow, young leaves are yellowish gray or reddish gray, first on the upper young leaves ), Sulfur deficiency (leaves are not yellow, leaf chlorosis is yellowish purple), zinc deficiency (vein veins are not yellow, chlorosis between leaves and veins becomes brown, and can produce necrotic spots), nitrogen deficiency (vein veins are not yellow, usually in the old Occurrence of leaves, yellowish-green in young leaves, and later become yellow) and other factors, can also lead to the occurrence of "yellow leaves", should pay attention to symptomatic treatment.
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