Detailed Explanation of Common Cotton Diseases and Their Control Techniques

I. Damping-off

Cotton damping-off, commonly known as root rot and black root disease, occurs in all cotton regions nationwide. After cotton seedlings are affected, yellow-brown lesions appear at the base of the stem near the ground, then turn dark brown and gradually become sunken and rotten. In severe cases, the diseased part becomes thin, and the diseased seedlings wither and die or topple over. After the cotyledons are affected, irregular yellow-brown lesions form, and later the diseased part breaks and falls off, becoming perforated. After adult plants are affected, brown spots appear on the leaves, which later fall off and become perforated.

Control methods: 1. Reasonable crop rotation: with gramineous crops: rotate for more than 2-3 years. 2. Reasonable fertilization: finely prepare the land and increase the application of decomposed organic fertilizer or 5406 bacterial fertilizer. 3. Improve sowing quality: for spring cotton, the suitable sowing period is when the soil temperature at a depth of 5 cm reaches 14°C, and generally sowing at a depth of 4-5 cm is appropriate. 4. Strengthen seedling-stage management: thin seedlings appropriately early, cultivate frequently, reduce soil moisture, raise soil temperature, and cultivate strong seedlings. 5. Chemical seed dressing: select seeds carefully and dress them with 50% carbendazim at 0.5-0.8% of seed weight, or 50% thiophanate-methyl at 0.6% of seed weight.

II. Fusarium wilt

Fusarium wilt is also called the cancer of plants and is a major enemy of cotton production. In recent years, it has spread rapidly. The characteristics of Fusarium wilt are: plant dwarfing, leaves turning grayish green, brittle and hard, stem bending, shortened stem nodes, sunken growing point, and vascular bundles inside the stem turning gray-brown or light black. Conditions for onset: high temperature and high humidity, continuous cropping, and sunny days after rain can cause death in rows and patches.

Control methods: 1. Soil improvement: on the basis of applying organic fertilizer, nitrogen, phosphorus, and potassium, apply 0.5 kg of continuous-cropping agent per mu, then plow, which can kill most soil pathogens, increase soil aeration, eliminate nitrite content in the soil, break up compaction, improve saline-alkali soil, enhance plant disease resistance, and reduce the harm of Fusarium and Verticillium wilt. 2. Apply nitrogen fertilizer in an appropriate amount. 3. Water at the right time: when the average number of bolls per cotton plant reaches two and the weather is dry, apply the first irrigation; watering too early will promote disease occurrence. 4. During the seedling stage, bud stage, and flowering and boll stage, regularly spray 24 times with Kuhuang Jijiu, or with hymexazol and other treatments, to control Fusarium and Verticillium wilt. 5. For plants that have already developed the disease, surgery can be used for control: make a 2-3 cm vertical cut with a small knife at 5-6 cm on the base stem of the cotton plant, and insert two sections of matchsticks soaked for more than 4 hours in the original solution of Kuhuang Jijiu. The above method can effectively control the harm of cotton Fusarium wilt and can also control Fusarium wilt in other crops.

III. Black rot

Black rot: the epidermis of cotton roots is black, slightly raised, with no new roots growing. The plant is short, the leaves are soft, and growth is slow. It is prone to death under high temperature. After death, the plant appears black and withered but remains upright and does not fall over, and the affected area appears in patches. This disease is likely to occur in plots with long-term water accumulation after rain, low-lying terrain, relatively severe saline-alkali conditions, or large amounts of nitrogen fertilizer applied, where intertillage is not timely, and where the previous crop was sweet potato, sugar beet, Chinese cabbage, cabbage, or radish.

Control methods: 1. Level the land, prevent water accumulation, and drain water in time. 2. After rain, intertill in time to loosen the soil and improve aeration, enhancing root activity. 3. Increase the application of lime powder at 15 kg per mu, ferrous sulfate at 10 kg, or apply continuous-cropping agent or Feilibao, all of which can reduce and control the occurrence of this disease. 4. Increase the application of organic fertilizer and phosphorus and potassium fertilizers, and control and apply nitrogen fertilizer in an appropriate amount. 5. During the disease period, use 20 g each of Kuhuang Jijiu and Fulansu Kang, add 15 kg of water, and spray on the leaves or irrigate the roots, which can effectively control black rot.

IV. Viral disease

Cotton viral diseases mainly include small-leaf viral disease, mosaic viral disease, vein-curling wilt disease, and purple-leaf viral disease causing leaf drop, flower drop, and fruit drop. Viral disease is called the AIDS of plants. It spreads quickly, causes severe harm, and reduces yield invisibly, making it the number one enemy of plants.

Control methods: in the early growth stage of cotton, Bingdu Yisheng, Kangdusu, Bingdu Limie, or Kubingling can all be used for control.

V. Stem blight

Cotton can be affected from the seedling stage to the boll-setting stage. In the early stage, it harms the cotyledons, true leaves, stems, and growing points, causing seed rot, leaf spots, stem blight, broken tops, and leaf drop, and even death of the whole plant. In the later stage, it infects the bracts and green bolls, causing leaf drop and hard locks. The cotyledons and true leaves initially develop small yellow-brown round spots with purplish-red edges, which later expand into nearly round or irregular brown spots with many small black dots scattered on the surface (pathogens). When the stem and petiole are affected, small reddish-brown spots appear at first, then expand into dark brown spindle-shaped canker spots with sunken centers and purplish-red surroundings. When the disease is severe, the diseased part breaks and falls off, and the stems and branches die.

Control methods: 1. Reasonable crop rotation and reasonable close planting to improve ventilation and light transmission conditions. 2. Seed dressing: after delinting cotton seeds with sulfuric acid, dress them with a seed coating agent made of carbofuran and carbendazim at a ratio of 1:0.5, which both prevents disease and also controls aphids. 3. Spraying: when disease occurs at the seedling stage or adult plant stage, spray with 65% zineb 800-fold solution, or 70% thiophanate-methyl 1000-fold solution for control.