What to Do About Cotton Plant Death? A Detailed Guide to Targeted Control Techniques
In recent years, in some old cotton-growing areas, the problem of cotton "plant death" has become increasingly serious, causing losses for many cotton farmers. Although control measures have been applied, the situation has worsened year after year, with unsatisfactory results. Therefore, cotton disease control should follow the principle of "prevention first, treatment second" to reduce the incidence of cotton disease.
1 Control of oomycete diseases
In recent years, the promotion of disease-resistant and pest-resistant cotton varieties has changed the diseases causing cotton "plant death." The most important of these are oomycete diseases, with 60%-70% caused by oomycetes such as Phytophthora or Pythium. Diseases originally caused by fungi such as Fusarium and Rhizoctonia still occur and remain severe, but none are as damaging as oomycetes. Therefore, cotton "plant death" should be controlled at the seedling stage, mainly by root drenching or root watering, using fungicides with good efficacy against oomycetes, such as famoxadone (Yikuaijing), propineb (Antaisheng), combined with the root-strengthening and bacterium-promoting type 2116, or Yingtian No. 2, etc.
2 Control according to disease type
The types of cotton diseases have changed. Diseases that damage cotton roots and stems and cause "plant death" include Fusarium wilt, Verticillium wilt, Rhizoctonia damping-off, Pythium damping-off, Phytophthora blight, basal rot, stem rot, root rot and more than a dozen others, which may be oomycete, fungal or bacterial in nature. Different diseases require different control methods and should be treated differently with appropriate measures, including integrated fungicide application. For example, cotton Fusarium wilt occurs over large areas and causes great damage; treating it after patches of dead plants appear is too late. It is best to apply the first treatment at the early stage of disease onset, generally before the wheat harvest, in mid-May, when the red-green mottling on cotton plants has not yet disappeared; at midday when it is hot and dry but the cotton field is not dry, and individual cotton plants wilt as if from drought, this is the time to begin the first spraying, or even earlier. Using a fungicide for Fusarium and Verticillium wilt at 10 d intervals, applied for 3-5 d continuously, can eliminate the disease. If the disease has already occurred and caused patches of dead plants, spraying can only control further spread.
3 Control of soil-borne diseases
In plots where cotton has been grown continuously for many years, physiological diseases and root diseases are most obvious. Soil-borne diseases mainly include Fusarium wilt and root rot. They begin infecting from the roots and spread through the vascular bundles to the stems, leaves, bolls and other parts. In affected cotton fields, many cotton plants die from the seedling stage; even if seedlings are replanted, some plants may still wilt at the boll stage, and some may die. Therefore, soil disinfection of the cotton field should be carried out before planting. Before sowing, evenly broadcast cotton-specific soil purifying agent on the surface of the sowing strip, and mix it in by manual turning (for manual sowing) or with the seeder. Before or during sowing, apply cotton-specific soil purifying agent in furrows 10-12 cm below the sowing furrow, or 8-12 cm to one side of the sowing furrow. The soil purifying agent must be kept at a certain distance from the cotton seeds and must not directly contact the seeds to avoid phytotoxicity. Because soil-borne diseases are widely distributed, completely eliminating them also requires reasonable crop rotation, deep plowing and sun-exposing of soil clods, and high-temperature disinfection techniques.
4 Control according to climatic conditions
Cotton disease occurrence follows certain patterns. It is most prone to occur in spring at low temperatures, in summer at high temperatures, after rain, and after watering when soil moisture is high. More than 10 consecutive days of overcast and rainy low-temperature weather, with temperatures of 18-25°C, is the optimal temperature range for Verticillium wilt to develop and spread. Large numbers of pathogens multiply and clog the vascular bundles of cotton plants, affecting the transport of water and nutrients, so leaves wilt and even drop. During the dog days, after each heavy rainfall, there will be a peak of Verticillium wilt incidence.
Every summer there are several high-temperature peak periods. When these occur, cotton plants become diseased, and the onset is sudden and difficult to control. Improper control can cause large areas of plant death, severe yield reduction, or even total crop failure. In high-temperature weather, spraying fungicides plus nutrient solutions for prevention, applied 2-3 times continuously, can effectively prevent cotton disease occurrence.
5 Change planting methods
Most cotton-growing areas (especially northern cotton areas) do not have the habit of raising seedlings and instead use direct seeding, because cotton sowing time is from late April to early May, often encountering "late spring cold" or "overcast and rainy" weather, resulting in a pattern of root diseases dominated by Phytophthora and Pythium about 1 month after sowing. Therefore, the seedling-raising and transplanting method should be adopted, with basal application of bio-organic fertilizer or seed dressing with microbial fertilizer to promote root development and reduce the occurrence of harmful pathogens in the rhizosphere.
6 Control cotton "plant death" as early as possible
① Treating too late or not treating at all is the main cause of cotton "plant death," so control should be carried out at the seedling-thinning stage. ② Pay attention to the spread of pathogens through rain, cultivation and other pathways, and take preventive measures. Apply chemical fertilizers (such as diammonium phosphate and compound fertilizer) reasonably, and apply more fully decomposed organic fertilizer. Pay attention to the characteristics of microbial fertilizers in resisting Fusarium and Verticillium wilt pathogens. Cotton "plant death" must be prevented early, especially for plastic-film mulched cotton, where oomycetes occur early, roots are shallow, and disease is severe. Control measures should include increasing the application of bio-organic fertilizer, balanced fertilization, timely early disease prevention to minimize losses, and cultivation measures such as timely film removal, combined with topdressing, hilling and watering.