Occurrence and Control of Cotton Seedling Diseases

The occurrence of cotton seedling disease is characterized by concentrated onset time, which usually occurs 15-30 days after sowing. The primary infection source is mainly from soil and a few from seeds. Around April 20 this year, there was continuous rain and low temperatures in many provinces, and the occurrence of seedling disease was bound to be serious, so all localities should prevent and control it in time.

First, symptom manifestation

(1) blight. Damage to cotton seedlings before they are unearthed will cause rotten seeds and sprouts. The disease occurred after the cotton seedlings were unearthed, and the disease spot appeared at the base of the young stem near the ground and then became black and sunken, which gradually expanded, surrounded the whole stem base, and finally caused the seedling to wither and die. When the diseased seedlings are pulled up, it can be seen that there is often mycelium adhesion between the diseased part and the surrounding soil. After the damage of cotyledons, irregular yellow-brown spots appeared in the middle of the cotyledons, and the disease fell off in the later stage, forming perforation.

(2) anthrax. The disease occurred before cotton seedlings were unearthed, and the hypocotyls and young roots turned brown and rotted. The disease occurred after the cotton seedlings were unearthed, and the small reddish-brown spots appeared at the base of the stem, then expanded into purple-brown sunken fusiform stripes, the disease spots were often longitudinally cracked and constricted, and the cotton seedlings were easy to die from waist fracture. Under wet conditions, the disease spot can develop to the depth, reaching the top of the young stem to form the top rot. The root is dark brown and semi-wet rot after being dyed, and it is not easy to break after being pulled up. Cotyledons often produce semicircular light brown to brown disease spots on the edge of the leaves, and the edges are reddish brown; under wet conditions, orange sticky spores are produced on the surface of the disease spots.

(3) Red rot. The cotton seedlings were damaged before they were unearthed, and the buds turned yellowish brown and rotted. After the cotton seedlings were unearthed, the root tip first became light yellow, and then became brown and rotten, and gradually spread to the whole root; the base of the young stem first became yellowish brown, then turned dark brown and rotted, and the disease spot was not sunken; the tender stem of the main root and the ground was damaged, it will become thicker and produce short brown stripes, which is the main feature of the disease; cotyledons are damaged, and most of them produce grayish-red irregular or nearly round spots at the edge, and the disease spots often break. A pink mildew layer is produced in the disease part under wet conditions.

(4) sudden collapse. The main symptoms are that the seedlings soften and lodge in the form of light brown water from the base up, and the cotyledons also show water-stained softening and discoloration immediately, and the disease develops rapidly, so it is called sudden fall disease. Most of the pathogens invaded from the young roots and spread to the young stems and the whole seedlings. When the soil moisture is high, seeds and newly germinated buds can also be infected, affecting seedling emergence or forming weak seedlings. White fine floc can sometimes be seen on the fallen dead seedlings.

Second, the conditions of the disease.

(1) Climatic conditions. High humidity is needed for the growth, reproduction and infection of pathogens at seedling stage. Therefore, if the seedling encountered overcast and rain or high soil moisture and low soil temperature, it is beneficial to the occurrence and development of the disease. If you encounter a low temperature below 10 ℃, the seed will rot. Two weeks after cotton seedlings were unearthed, the nutrients of cotton seeds had been exhausted, and the ability of cotton seedlings to produce nutrients was weak. at this time, the disease resistance of cotton seedlings was very poor, and it was easy to induce diseases.

(2) seed quality. Seed maturity is low, or damp mildew, easy to rot, rotten bud, not only is not conducive to emergence, but also after emergence are mostly weak seedlings, easy to disease.

(3) sowing quality. The cotton seed is full, the vitality is strong, unearthed quickly, the seedling is strong and disease resistant. On the contrary, the unearthed is slow, the seedling is weak and not resistant to disease.

(4) farming and cultivation measures. The bacteria in the soil of continuous cropping cotton field accumulated year after year and the disease was serious. In the cotton fields with low-lying terrain and poor drainage, the soil moisture is high, the ground temperature is low, the ventilation is poor, the root system of cotton seedlings is not well developed, and it is easy to occur; extensive soil preparation or tillage, too much bumpy soil, or too thick soil cover during sowing all affect the emergence of cotton seedlings, and the disease is serious; sowing too early, too deep cotton seedlings unearthed slowly, easy to occur.

III. Prevention and control methods

Because there are many kinds of cotton seedling diseases, several diseases often occur mixed, and affected by environmental conditions and the disease resistance of cotton seedlings themselves, so in the prevention and control, we should do a good job of seed disinfection and soil treatment on the basis of seed disinfection and soil treatment. focus on cultivation management and chemical control measures at seedling stage.

(1) cultivation management. After cotton emergence, the ability to absorb inorganic nutrients is weak, the leaf area is small, the organic nutrients produced by photosynthesis are not sufficient, coupled with the impact of adverse climatic environment, root growth is more difficult, which aggravates the occurrence of diseases. Therefore, cotton seedling ploughing and raising soil temperature are the necessary means to solve the seedling disease.

(2) Chemical prevention and control. Spraying Tianda-211 solution with 600 × 800 times of drought resistance and strong seedling type after cotton emergence can improve the ability of low temperature resistance and disease resistance of cotton seedlings. At the initial stage of the disease, 50% carbendazim or 70% methyl topiramate wettable powder can be sprayed 800 times and 70% mancozeb 600 times, once every 7 days, twice in a row. The effect of fungicide combined with foliar fertilizer is better.