Occurrence and Control of Cotton Root Rot in Northern Xinjiang

In 2007, northern Xinjiang suffered varying degrees of cooling and rainfall in April, May and August, respectively. Cotton root rot occurred seriously, and the incidence of cotton fields reached 20% to 50%, which had a certain impact on cotton production in northern Xinjiang.

Symptoms of the disease

The pathogen overwintered with chlamydospores on the plant remains in the soil and germinated and infected the following year. After the cotton was infected, the leaves shrunk or wilted, and soon fell down and died. The base and root of the diseased seedling were purple-brown, gradually rotted, the cortex was dry-rotten, pulled out from the soil, and the root was rotten brown. When the humidity is high, the root rot disease spreads quickly, and the disease part has original hyphae and inner conidia, resulting in gray-white mildew layer. At the stage of 3 to 4 leaves, the temperature increased and the disease developed slowly. From late July to cotton boll opening, obvious symptoms appeared in the field due to rainfall and low temperature. during the boll opening period, the leaves wilted and drooped, withered rapidly, but did not fall off immediately, the root was swollen and twisted, the base and root of the stem were purple-brown and brown after drying up, and the diseased epidermis was split. The diseased root was thinner than the normal root, and the lateral root increased. Generally, the pathogens rarely invaded the endothelium, the vascular bundles were white, and the bolls of diseased plants decreased significantly.

Second, the cause of the disease

1. Climatic factors

After cotton sowing, low temperature, rainfall and late spring cold often lead to the occurrence of root rot. Cotton is a temperature-loving crop with rainy and low temperature in spring, low soil temperature, slow emergence of cotton seedlings and poor resistance to cotton seedlings, which increases the chance of pathogen infection.

two。 Seed quality

The seeds with full grains and good maturity have strong vitality, emerge quickly after sowing, and are not easy to be infected by pathogens, while the seeds with poor maturity and high damage rate seriously affect the emergence rate, such as low temperature, root rot occurs seriously, causing a large number of rotten seeds and dead seedlings.

3. Sowing quality

Sowing too early and too deep will affect the emergence of cotton seedlings and increase the chance of pathogens infecting seeds and seedlings, and the resistance of cotton seedlings is poor and susceptible to disease.

4. Soil condition

The incidence of root rot in low humus and alkaline soil is generally serious; high groundwater level and poor soil permeability will also increase the incidence of root rot. In northern Xinjiang, the incidence of sandy loam is more serious than that of loam. Attention should be paid to balanced fertilization. Partial fertilization will cause malnutrition and premature senility during the growth period of cotton, and reduce disease resistance.

5. cropping system

Continuous cropping for many years will cause the accumulation of soil bacteria and aggravate the occurrence of soil diseases. At the same time, continuous cropping will lead to the deterioration of soil structure, nutrient imbalance, and root rot is very easy to occur after unfavorable conditions.

III. Prevention and control measures

1. Seed selection

Select improved varieties with full grains, high germination rate and strong germination potential, requiring purity ≥ 90%, germination rate ≥ 80%, moisture content ≤ 12%, damage rate ≤ 5%, uniformity ≥ 95%.

two。 Soil preparation

Autumn ploughing and winter irrigation is carried out in autumn, and the depth is 25cm to 30cm. The bacteria-carrying plants in the surface layer are turned deep into the deep soil to decompose. Winter irrigation can also avoid unfavorable conditions such as soil over-wetness and consolidation caused by spring irrigation. The quality of soil preparation before sowing should reach the standard of "uniform, flat, loose, broken, clean and moisture", which can promote the rapid emergence of cotton seedlings and reduce the occurrence of root rot.

3. Seed treatment

0.2% methyl topiramate, 0.5% carbendazim, 0.3% mixed seed ling and 0.3% dimethazone 30 kg water can be used to mix seeds 100 kg. Seed coating agents containing plant growth regulators, fungicides, pesticides and trace elements were used to prevent the occurrence of cotton seedling diseases.

4. Suitable time for sowing

The temperature in spring in the cotton area of northern Xinjiang is low, and cold and frost often occur in late spring, so early sowing is easy to cause rotten seeds and dead seedlings, so the appropriate sowing date should be selected according to the climatic conditions. In northern Xinjiang, when the soil temperature of 5 cm is above 14 ℃, that is, sowing begins in mid-April, with a depth of 2 cm to 3 cm.

5. Field management

The incidence of root rot can be reduced by ploughing and loosening the soil in time after cotton emergence, early ploughing, deep ploughing and diligent ploughing, breaking the hardening in time after rain, increasing soil temperature and soil permeability. Balanced fertilization, organic and inorganic combination, a large number of trace combination to ensure the steady growth of cotton, enhance disease resistance, and prevent cotton from premature senescence in the later stage.

6. Rational crop rotation

Rotation of crops such as corn, soybean and rape can improve soil conditions and balance soil nutrients, which can not only effectively prevent the occurrence of cotton root rot, but also curb the occurrence of malignant weeds in cotton.

7. Resistant variety

The disease-resistant varieties suitable for planting in northern Xinjiang are Xinluzao 26, 28, 31, 33, 36 and so on.