Occurrence and Control of Common Boll Diseases in Cotton

Cotton boll disease is a compound disease caused by many diseases, which is often manifested as rotten bolls, which affects not only cotton yield but also cotton quality. The loss caused by rotten bolls amounts to more than 10% of the total output. The common boll diseases in cotton fields in Henan Province are boll blight, anthracnose, red rot, powdery mildew, black fruit and so on. Most of them occur in rainy years in mid-and late-August, especially in days of overcast and rain, when the disease is hot and humid.

First, symptoms of bell disease

Boll blight: the disease often occurs in the lower part of the cotton plant. The disease begins at the base, seam or tip of the boll, and begins to appear dark cyan water stains, gradually develops to the whole boll, becomes bluish brown, and finally becomes a black oil-like irregular spot, the edge color is lighter, and the boundary between the diseased part and the healthy part is not obvious. If the environmental conditions are suitable, the whole boll face becomes greenish brown or black after the disease for 5 days, and then a thin layer of downy mildew is produced on the boll surface, and the cotton boll turns black and rotten or becomes a stiff valve. The shell of bolls with late onset blackened, which had little effect on cotton.

Anthrax: at the initial stage, dark red dots often occur near the bell tip, and gradually expand into brown round spots, with purplish red edges, slightly protuberances and depressions in the middle. When the climate is humid, a reddish-brown sticky substance is produced in the middle of the disease spot. In severe cases, the diseased bell stops growing, rots or becomes a stiff flap. The mildly ill early puff, the cotton is brown.

Red rot disease: the disease spot mostly occurs from the base, tip or seam of cotton boll, which is immersed in dark green water at the initial stage, and then extends to the whole boll, causing black rot and pink or pink mildew layer on the surface.

Powdery mildew: its symptoms are similar to those of red rot, except that the mildew layer is thicker, showing a loose fluffy substance, and the mildew layer becomes pink and white when it is wet, while the mildew layer of red rot is thin and tight.

Black fruit disease: the damaged cotton boll began to turn light brown, the whole boll was soft, and the boll face gave birth to protuberant dots in the later stage, which showed white at first and then developed into black. In order to seriously damage the cotton boll, the boll shell is stiff, covered with a gray-black mildew layer, becoming a soot-like black fruit, often does not fall off, stiff on the fruit branch, the internal fiber becomes a gray-black hard knot, can not crack.

II. Prevention and control methods

Agricultural prevention and control: ① intercropping. The intercropping of cotton grain, cotton potato, cotton radish and other forms of intercropping can increase the ventilation and light transmission conditions of the cotton field, reduce the field humidity, create ecological conditions conducive to the growth of cotton but not conducive to the occurrence of diseases, and increase income. ② fertilized rationally. Avoid applying too much or too late nitrogen fertilizer and increase the amount of phosphorus and potassium fertilizer. The suitable ratio of nitrogen, phosphorus and potassium is 1: 0.4 / 0.4 / 0.8. Apply more farm manure. ③ reasonable irrigation and drainage. Do not flood irrigation, it is better to use trickle irrigation. Drainage should be carried out in time after rain to reduce humidity in the field. ④ fine pruning. Pruning, beating old leaves and pulling out empty plants in time to increase the ventilation and light transmission conditions of cotton fields. The fallen branches and leaves were taken out of the field and buried. ⑤ picks up the sick bell. Pick the cotton bolls that have been diseased in time. The age of cotton bolls is more than 40 days, and the internal fiber has grown. If the disease is not picked, the disease will rot and spread rapidly, and a certain yield can be recovered after picking. The diseased bell can be dipped in 1% ethephon solution before drying.

Chemical control: generally, cotton bolls begin to fall ill 30 days after flowering. When there are some green bolls in the lower part of the cotton field, 80% mancozeb, 58% metalaxyl manganese zinc, metalaxyl thiram or diazolone should be sprayed in time to protect the cotton bolls. Spraying in the early stage of the disease can also control the progression of the disease. Adding 27% high fat film during spraying can form a film on the surface of cotton boll to prevent bacteria from invading and Rain Water from scouring, so the protective effect is better.