How to prevent and control cotton root rot in northern Xinjiang? Understanding the patterns of occurrence is key

In 2007, northern Xinjiang suffered varying degrees of cooling and rainfall in April, May and August respectively, and cotton root rot occurred rather severely, with the disease incidence in cotton fields reaching 20%-50%, causing a certain impact on cotton yield in northern Xinjiang.

1. Disease symptoms

The pathogen overwinters as chlamydospores on plant residues in the soil and germinates to infect the following year. After cotton is infected, the leaves shrink or wilt, and soon afterward the plant lodges and dies. The stem base and roots of diseased seedlings are purplish brown and gradually rot, with the cortex drying and rotting; when pulled from the soil, the roots are decayed brown. When humidity is high, root rot spreads quickly, and the diseased parts bear protohyphae and endoconidia, producing a grayish-white mold layer. At the 3-4 leaf stage, as the temperature rises, the disease develops slowly. From late July to the boll-opening stage of cotton, due to rainfall and low temperature, obvious symptoms appear in the field again; at the boll-opening stage the leaves wilt and droop, rapidly turning green-wilted, but they do not drop immediately, the roots become swollen and twisted, the stem base and roots are purplish brown and turn brown after drying up, and the epidermis of the diseased parts cracks. Diseased roots are thinner than normal roots, with increased lateral roots. The pathogen generally invades the endodermis less, the vascular bundles are white, and boll setting of diseased plants is markedly reduced.

2. Causes of the disease

1. Climatic factors

After cotton sowing, low temperature, rainfall and late spring cold often induce major outbreaks of root rot. Cotton is a warm-loving crop; rainy and low-temperature conditions in spring, with low soil temperature, cause cotton to emerge slowly, and the poor resistance of cotton seedlings increases the chance of pathogen infection.

2. Seed quality

Seeds that are plump and well matured have strong vitality, emerge quickly after sowing, and produce uniform and robust seedlings that are less susceptible to pathogen infection; whereas seeds with poor maturity and a high breakage rate seriously affect the emergence rate, and if low temperature occurs, root rot becomes severe, causing large numbers of rotted seeds and dead seedlings.

3. Sowing quality

Sowing too early and too deep both affect cotton emergence and increase the chance of the pathogen infecting seeds and seedlings, and the cotton seedlings have poor resistance and are prone to the disease.

4. Soil conditions

Soils low in humus and on the alkaline side generally have severe disease; a high groundwater table and poor soil permeability also increase the probability of root rot occurrence. In northern Xinjiang, sandy loam soils have relatively severe disease while loam soils have relatively light disease. Attention should be paid to balanced fertilization; one-sided fertilization causes nutrient imbalance and premature senescence during the cotton growth period and reduces disease resistance.

5. Cropping system

Many years of continuous cropping cause accumulation of soil pathogens and aggravate the occurrence of soil-borne diseases. At the same time, continuous cropping leads to deterioration of soil structure and nutrient imbalance, and root rot is very likely to occur when unfavorable conditions are encountered.

3. Control measures

1. Seed selection

Select good seeds that are plump, with a high germination rate and strong germination vigor; the requirements are purity >= 90%, germination rate >= 80%, moisture content <= 12%, breakage rate <= 5%, and uniformity >= 95%.

2. Soil preparation

Carry out autumn plowing and winter irrigation in autumn, with deep plowing of 25-30 cm, turning the pathogen-bearing plant material on the surface deep into the soil so that it rots and decomposes. Winter irrigation can also avoid unfavorable conditions such as excessively wet soil and compaction caused by spring irrigation. Before sowing, the land preparation quality should meet the 6-character standard of "even, level, loose, fine, clean, moist", which can promote rapid cotton emergence and reduce the occurrence of root rot.

3. Seed treatment

You can use 0.2% thiophanate-methyl, 0.5% carbendazim, 0.3% fenaminosulf and 0.3% dexon with 30 kg of water to treat 100 kg of seed. Coating with a seed dressing agent containing plant growth regulators, fungicides, insecticides and trace elements prevents the occurrence of cotton seedling diseases.

4. Sowing at the right time

Spring temperatures in the cotton region of northern Xinjiang are low, and late spring cold and frost often occur, so sowing too early easily causes rotted seeds and dead seedlings; therefore the appropriate sowing time should be chosen according to climatic conditions. In northern Xinjiang, generally when the temperature of the 5 cm soil layer is above 14°C, that is, sowing begins in mid-April, with a sowing depth of 2-3 cm.

5. Field management

After cotton emergence, carry out timely intertillage and loosening of the soil - early intertillage, deep intertillage, frequent intertillage - and promptly break up compaction after rain to raise soil temperature and increase soil permeability, which can reduce the incidence of root rot. Fertilize in a balanced way, combining organic and inorganic fertilizers and combining major and trace elements, to ensure steady growth of cotton, enhance disease resistance, and prevent premature senescence in the later stage of cotton.

6. Reasonable crop rotation

Rotating with crops such as @#@245@#@, corn, soybean and rapeseed can improve soil conditions and balance soil nutrients, not only effectively preventing the occurrence of cotton root rot but also curbing the occurrence of malignant weeds in cotton.

7. Disease-resistant varieties

Disease-resistant varieties suitable for planting in northern Xinjiang include Xinluzao No. 26, No. 28, No. 31, No. 33, No. 36, etc.