First, weakened root absorption capacity, malnutrition
The wilting leaves developed from top to bottom and from the outside to the inside, the leaves did not whitish green, and the roots and cuttings were free from lesions. This situation is mainly due to prolonged drought, lack of water or soil moisture, and lack of oxygen in the soil, resulting in poor development of cotton roots, absorption of nutrients blocked, resulting in malnutrition; if you suddenly drop heavy rain or encounter continuous rain, more serious . In general, sandy soils, infertile soils, saline-alkali soils, insufficient base fertilizers, and cotton fields lacking potassium fertilizers are relatively heavy. It is necessary to pay special attention to the fact that cotton fields where this situation occurs can easily cause premature senescence in the middle and later stages, resulting in greater losses. In the middle and late stages, the typical symptoms can be expressed as the following: (1) The base of the petiole becomes soft, and the water loss shrinks. (2) Leaf edges appear yellow, leaf tissue chlorosis, but the veins remain green; later, the leaf color changes from yellow to purple, the leaves shrink and become brittle. 3 When the leaves are littered, the top of the stems is in a dry coke shape, and a large number of bud bells fall off. 4 Roots are stunted. The main roots are short and fine. They often become "chicken roots". The number of roots and fibrous roots is significantly reduced. The color is dark brown and the tip is brown and rot.
Suggested countermeasures: If the soil is arid, it should be watered in time. If the soil moisture is high, the cultivator should disperse it in time. Insufficient application of base fertilizer, especially cotton fields with suspected doubts on the quality of base fertilizers and less potassium use, should be topdressed with potassium and phosphate fertilizer as early as possible to supplement nutrition. In addition to the above measures, potassium dihydrogen phosphate, dipotassium dihydrogen phosphate, six-in-one yield increasing factor, cotton disease-resistant high yielding factor, high-boron high-potassium, and diammonium phosphate aqueous solution may be used to spray the leaves of the cotton plant. Relieve symptoms.
Second, cotton black root rot
After the occurrence of the disease, the first supply of cotton leaves is insufficient, the leaves are wilting during the day, and can be recovered sooner or later, and the entire cotton plant is wilted and the leaves are blue and dry. When the diseased plant was pulled out, the main root wood layer appeared light brown, and its section showed a dark brown lesion (but no lesion was found on the stem). The snoring caused by malnutrition, drought, and lack of water causes the roots to have a normal tender color. The occurrence of black root rot in the seedling stage is heavier. On the contrary, it does not occur or is very light.
The typical differences between the above-mentioned nutrient disorders are as follows: 1 The cotton seedlings are slightly dwarfed or dwarfed, the leaves are shrunk or wilted, and blue and dry in severe cases. 2 The stems and roots of the diseased seedlings were purple-black and gradually rotted. After drying, the cortex was rotted brown and the epidermis of the diseased section was longitudinally split and easily fell off. When the humidity is high, the diseased part produces a gray and white mold layer, which is a pathogenic mycelium and an internal conidia. 3 Sick root is thinner than root and lateral roots are increased. The four subcutaneous tissues became dark and brittle, and the base of the roots became swollen and swollen. The number of boll strains decreased significantly. 6 The cotton boll opening period is the peak of onset, the leaves are wilting and drooping, and quickly blue and dry, but the leaves do not fall off immediately.
Pathogen is a semi-known fungus Rhizoctonia genus, Lepidium nodosum, which has a wide host range and can infect a variety of plants such as Leguminosae, Solanaceae, Cucurbitaceae, Malvaceae. The spores of the pathogen can survive in the soil for many years and can re-infect wintering on the sick body. The occurrence of diseases is closely related to the temperature. The soil temperature of 15 ~ 20 °C is conducive to the invasion of pathogens and disease development, less than 15 °C, higher than 27 °C rare disease, the temperature above 30 °C is difficult to disease. Cotton field for many years continuous cropping, soil viscosity, slightly acidic to alkaline, high humus content, low-lying terrain, flood irrigation, long-term soil moisture, etc., conducive to disease.
Suggested countermeasures: After the onset, 50% carbendazim 600-fold solution, 6-gao-lic acid I-garicin 1000-fold solution, one-limb 3000-time solution, 70% diuresis 500-fold solution, and 70% hymexazol may be used. Liquid, at the same time choose to add alizarin lactone, DA-6, agroxigenin, sodium nitroprusside, cytokinin and other regulators or the above-mentioned mixed spray foliar fertilizer, generally can be sprayed twice. At the same time as spraying, the use of liquids for severely infected plants can be applied to the roots of cotton plants, with outstanding results.
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