Cotton shows disease symptoms, integrated control with multiple measures
Symptom identification of cotton Fusarium wilt and Verticillium wilt
Cotton Fusarium wilt can occur throughout the entire growth and development period of cotton, but it occurs more severely at the seedling stage. If favorable conditions occur, it can also break out heavily at the adult plant stage. Sudden wilt type: leaves suddenly lose water, droop and wilt, leaf color is dark green, leaves become soft and thin, the whole plant dries green and dies, but leaves generally do not fall off, and petioles bend. Yellowing type: can occur at both the seedling stage and the adult plant stage. The yellowing type mostly starts from the leaf margins, with part or all of the leaf turning yellow, and finally the leaf dies or falls off, and the vascular bundles in the petiole and stem partially turn brown. Purple-red type: mostly occurs at the seedling stage. Local or entire diseased leaves show purple-red diseased spots, and the veins in the diseased area also appear reddish-brown. The leaves then wilt and dry up, and the cotton plant dies. Crinkled type: can occur at both the seedling stage and the adult plant stage. The typical symptoms are leaf crinkling, thickening, dark green leaf color, shortened internodes, and dwarfed plants, which generally do not die. Yellow net-vein type: mostly appears at the seedling stage. The veins of diseased plants lose green and turn yellow, while the mesophyll remains green. Part or most of the leaf shows a yellow net-vein pattern, and finally the whole leaf wilts or falls off. Half-yellowing type: mostly occurs at the seedling stage. After infection, only one side of the cotton plant shows yellowing and wilting, while the other side grows normally. When it occurs together with Verticillium wilt, the symptoms appear as dwarfed wilting or blighting, etc. A longitudinal cut of the diseased stem shows dark brown stripes in the xylem. Acute blight type: mostly occurs at the adult plant stage. After heavy rain followed by sudden clearing, acute blight symptoms often appear in heavily diseased fields. Cotton plants suddenly lose water, wilt, dry green, and droop. Leaves, buds, and flowers fall off in large numbers, forming bare stems, and the top of the main stem and fruiting branches scorch and dry up.
Cotton Verticillium wilt can occur throughout the entire growth period, but under natural conditions symptoms rarely appear at the seedling stage. It generally begins about 40 days after sowing, at the cotton plant squaring stage, and the disease in the middle and late stages is obviously more severe than in the early stage. Yellow spot type: symptoms mostly appear at the squaring stage and develop relatively slowly. Diseased plants start from the lower leaves and gradually develop upward. In the early stage of the disease, leaf margins curl upward, and pale yellow irregular diseased spots form between the veins, while the areas near the veins remain green. Generally, they do not die early and the leaves do not fall off. Leaf blight type: leaves show localized blighted spots or palmate blighted spots. After the leaves blight, they fall off, but the cotton plant generally does not form bare stems. Wilting type: mostly occurs at the boll-setting stage. After each heavy rain, a kind of acute Verticillium wilt may appear. Water-soaked pale green patches form between the main veins of the leaves, and the leaves quickly wilt and droop. Defoliating type: affected plants generally show symptoms first on the upper leaves. The typical symptoms are leaf wilting and drooping, rapid falling off, and the cotton plant has already formed bare stems before dying.
Differences between cotton Fusarium wilt and Verticillium wilt: Fusarium wilt causes leaf veins to turn yellow, while Verticillium wilt causes leaf mesophyll to turn yellow; cotton plants with Fusarium wilt easily shed leaves and become bare stems, while cotton plants with Verticillium wilt show sudden leaf wilting and then shedding into bare stems only in certain years after long drought followed by sudden heavy rain or after soaking in heavy water; cotton plants with Fusarium wilt have a dwarfed plant type with shortened internodes, while cotton plants with Verticillium wilt generally do not become dwarfed, but plants that develop the disease earlier and are more severely infected sometimes become relatively short, though the symptoms are generally not obvious; after splitting the stem, the vascular bundles of plants with Fusarium wilt turn dark brown, while those of plants with Verticillium wilt turn light brown.
Highlight the word "resistance" in variety selection
Selecting varieties with strong disease resistance can effectively control the degree of disease, and it is the most critical basic factor in disease prevention. In this regard, it is recommended that the broad masses of cotton farmers look for varieties with strong disease resistance in the actual cultivation of cotton farmers around them, and absolutely do not easily believe the lies of "shills" who only know "how to sell more seeds for themselves and @#@3@#@." Only by selecting a variety with strong disease resistance recognized by the broad masses of cotton farmers in actual cultivation can it be ensured that cotton develops fewer diseases and uses less pesticide.
The quality of cottonseed includes two aspects: first, whether the variety's own disease resistance is strong or weak, and second, whether seed chemical treatment is good or bad. Under normal circumstances, enterprises producing excellent cottonseed with strong disease resistance, in order to make their cottonseed "even better," will use high-grade and highly effective seed coating agents such as Apron plus Metalaxyl, or Vitavax (carboxin plus thiram) for seed coating treatment, which has a very good effect on effectively reducing early-stage cotton diseases and alleviating late-stage diseases.
Highlight the word "strong" in field management
In field planting management, strengthening scientific planting management can not only effectively reduce the occurrence of cotton Fusarium wilt and Verticillium wilt, but is also more conducive to increasing cotton yield and efficiency.
Where conditions allow rotation and stubble changing, implement rotation and stubble changing with gramineous crops for more than 3 years as much as possible, so as to effectively reduce soil inoculum sources. In old cotton areas without conditions for rotation and stubble changing, measures such as winter plowing, deep plowing, and planting on high ridges can be adopted as much as possible.
In addition to measures before sowing such as sunning seeds (which can promote earlier emergence and help strong seedlings), appropriately late sowing (which can shorten the emergence period and promote strong seedlings), and formula fertilization (especially paying attention to stabilizing phosphate fertilizer, increasing potassium fertilizer, and supplementing micronutrient fertilizers, which can significantly reduce disease occurrence), practice in various places has proved that cotton seedling raising and transplanting is also a measure to reduce disease occurrence. Using nutritive bowls with disease-free soil for seedling raising or soilless seedling raising followed by transplanting can effectively reduce infection by pathogens at the seedling stage, delay disease onset, and significantly improve the disease resistance of cotton plants.
Cotton is a potassium-loving crop, and increasing potassium fertilizer can significantly reduce disease occurrence and help increase yield. However, under this year's situation of soaring fertilizer prices, many cotton farmers used compound fertilizers or blended fertilizers with low phosphorus and low potassium. If the content of pure phosphorus and pure potassium nutrients is relatively low, they should be supplemented in a timely manner at the full squaring stage to strengthen cotton plants and enhance disease resistance.
When watering, apply 0.5-1 kg of potassium permanganate per mu with the irrigation water, which can better inhibit disease occurrence.
Highlight the word "prevention" in chemical control
Compared with other varieties, cotton varieties with strong disease resistance develop milder disease under the same conditions, but this does not mean they "do not die at the seedling stage" or "do not die as plants" ("do not die at the seedling stage" and "do not die as plants" are often exaggerated claims by some seed sellers; currently no cotton variety can achieve "immune" resistance), nor does it mean that chemical control can be omitted.
Based on many years of experience in cotton promotion and planting, the author proposes the idea of "one control and two promotions" in chemical control, and summarizes several pesticide formulas, which have shown remarkable effects in practical application in some cotton planting areas in Hebei, Shandong, Henan, Anhui, Hubei, Tianjin, and other places. Specific method: fungicide (to control disease) plus nutrient agent (to promote strong seedlings) plus growth-promoting regulator (to promote strong seedlings).
Better fungicides include 80% carbendazim, Liugao brand ethylicin, 70% fenaminosulf, 3% polyoxin, Yizhiling, Bingchukang No. 3 (high-purity ethylicin plus synergist), 36% Miankujing (trichloroisocyanuric acid, must not be mixed with organophosphorus pesticides), 70% hymexazol, etc.
Better nutrient agents include premium potassium dihydrogen phosphate (beware of products on the market adulterated with magnesium sulfate), Hongfu diammonium aqueous solution, cotton disease-resistant and high-yield nutrient, boron-potassium-zinc trinity yield-increasing nutrient, titanium fertilizer, potassium fulvate, etc.
Better growth-promoting regulators include brassinolide, DA-6 (diethyl aminoethyl hexanoate), sodium nitrophenolate, Nongxi Shixiaosu, etc.
Method of use: choose one product from each of the above categories and mix them for use at the same time, paying attention to alternating use. Spray once as prevention in a timely manner before each rain or before watering, and spray once more after rain or after watering, which can effectively control the spread of pathogens and significantly reduce disease occurrence. While spraying, also apply root drenching treatment to severely diseased plants and cotton plants within a radius of 1 meter, and the effect is significantly better than spraying alone.