How to prevent and control cotton red leaf stem blight? A full analysis of control measures

I. Symptom identification

After the plant is affected, the leaves turn dark green and become thick and brittle, then small red dots are scattered on the leaves, and finally the whole leaf turns red while the veins remain green, which is red leaf stem blight. When the disease is severe, the base of the petiole becomes soft, loses water and shrinks, causing the leaves to wither and fall off, and the top of the stem becomes scorched and dry. At the same time, it easily triggers repeated infection by target spot and brown spot, causing the diseased plant to scorch and die. Some plants can still grow adventitious buds after the diseased leaves fall off. Plants with severe and early onset are short, with poor root development, and both the main root and lateral roots are short and thin.

II. Cause analysis

This disease is a non-infectious disease, that is, a physiological disease of cotton. It is caused by a combination of various abiotic factors. Environmental conditions such as fertilizer, water, soil, climate and farming systems are very closely related to the occurrence of this disease, among which drought and insufficient nutrition are the leading factors.

1. In the middle and late stages of cotton, vegetative growth and reproductive growth are vigorous, and the demand for fertilizer and water is large. Once fertilizer and water are insufficient during this period, the disease is likely to occur.

2. Long-term drought and high temperature, and lack of water in the soil plow layer, hinder the normal progress of metabolism, leading to physiological disorder and causing cotton plants to "age before growing old," resulting in severe disease.

3. Plants being in a low-potassium state for a long time easily causes the prevalence of this type of disease; in addition, applying too much nitrogen fertilizer in cotton fields makes plants grow vigorously, and more glycoside substances accumulate in the leaves. Some sugars are converted into glucosides (a type of anthocyanin), which can also induce the occurrence of red leaf stem blight; red leaf stem blight can also be caused by magnesium deficiency.

III. Conditions for onset

1. Related to soil water content

In the early growth stage of cotton, there is a lot of rain, the aboveground part of cotton grows quickly and the plant type is large, but the root system is shallow and its ability to absorb nutrients is poor, so it is susceptible to disease; in July to August, long-term drought and inability to irrigate in time easily cause water shortage in the plow layer, affecting the root system's absorption of nutrients and leading to severe disease; after a long drought in the cotton field, when there is a sudden rainstorm followed by clear weather, plant transpiration increases sharply. Because there is too much soil moisture, root absorption is affected, underground nutrients and water cannot enter the plant, and aboveground organic nutrients cannot be formed, transported or distributed, causing physiological disorder in cotton plants and therefore severe disease.

2. Related to fertilization level

Cotton fields with sufficient base fertilizer and topdressing have robust plant growth and light disease; those without base fertilizer have more severe disease than those with base fertilizer; cotton fields without flower and boll fertilizer topdressing have severe disease; cotton fields where chemical fertilizer alone has been applied for consecutive years, especially those with excessive nitrogen fertilizer and no or little potassium fertilizer, have severe disease.

3. Relationship with cotton field soil quality

Sandy soil or poor soil with too shallow a plow layer has severe disease, because this type of cotton field has poor water and fertilizer retention capacity, and cotton plants have weak growth vigor and poor disease resistance.

4. Relationship with farming and cultivation systems

Cotton fields where the land is plowed too deep or too shallow during farming have severe disease, because this is not conducive to root growth and the absorption of water and fertilizer; in old cotton areas with long-term continuous cropping, soil fertility declines and disease is severe; for early-maturing varieties, insufficient or untimely fertilizer and water supply in the late growth stage easily causes the occurrence of this disease.

IV. Control methods

1. Intensive and careful cultivation

Level the land, deeply plow and improve the soil, combine land use with land maintenance, and enhance the soil's water and fertilizer retention capacity. In arid areas, cultivate frequently to reduce evaporation, promote cotton roots to grow downward and absorb water and nutrients from the soil, and improve drought resistance.

2. Apply heavy base fertilizer and skillful topdressing

Use more farmyard manure as base fertilizer. Where conditions permit, plant green manure or implement wheat-cotton rotation to supplement the lack of organic fertilizer, achieve the goal of improving soil and building soil fertility, and change the long-term practice of applying only chemical fertilizer, so as to avoid destroying soil aggregate structure and reducing fertilizer and water retention capacity; according to the fertilizer requirement patterns of cotton at each growth stage, apply topdressing skillfully. Generally, apply seedling fertilizer lightly, apply bud fertilizer as appropriate, apply heavy flower and boll fertilizer, and supplement with topping fertilizer; in the types of topdressing, pay attention to the combination of the three elements nitrogen, phosphorus and potassium, among which potassium fertilizer is especially important; in the late growth stage, for cotton fields already showing signs of premature aging, spray Handilong, potassium dihydrogen phosphate and urea early so that the leaves can directly absorb and use them, allowing the fertilizer effect to take effect quickly, with obvious effects of protecting leaves and increasing yield.

3. Reasonable drainage and irrigation

Cotton has different water requirements at different growth stages, needing little at the seedling stage and bud stage. However, during the flower and boll stage, cotton has a relatively large demand for fertilizer and water, and this often coincides unexpectedly with the summer drought and high-temperature season, so irrigation and fertilization should be done in time to achieve disease resistance and yield increase. In autumn, when there is a lot of rain, drainage should be done promptly to prevent poor root absorption and growth caused by waterlogging.

4. Apply heavy flower and boll fertilizer

Early-maturing varieties or early-sown cotton fields have cotton seedlings that develop early, set many bolls in the early stage and easily encounter the dry season, so the phenomenon of "aging before growing old" often appears. Therefore, flower and boll fertilizer should be applied early and heavily to ensure that fertilizer and water are shifted later and to ensure steady growth of cotton. In this way, the goal of reducing or preventing the occurrence of cotton red leaf stem blight can be achieved.