Diagnosis and Control of Cotton Seedling Diseases

Diagnosis and Control of Cotton Seedling Diseases

There are many kinds of diseases in cotton seedling stage, but they can be summarized into two types: root disease and leaf disease. Root disease often leads to seed rot before emergence, root rot and stem base rot after emergence, which are the main causes of lack of seedlings and broken ridges in cotton fields. the common diseases are standing blight, anthracnose, red rot, sudden fall and so on. The leaf disease is harmful to the cotyledons, true leaves and stems of cotton seedlings, and when it is serious, the top of the stem and leaves wither and fall off, such as black spot, brown spot, cotton seedling blight, stem blight and so on. This film focuses on an overview of the incidence rules of several common and harmful serious diseases at seedling stage, identification and diagnosis and comprehensive control measures of agriculture and chemicals, so as to provide reference and application for the majority of member cotton farmers in production practice.

Types and symptoms of diseases

Blight: blight, also known as root rot and black root disease, occurs in all cotton areas in China. Serious damage occurs in the cotton area of the Yellow River valley. Before cotton seedlings are unearthed, they often infect young roots and buds, causing rotten seeds and buds. After cotton seedlings are unearthed, yellow-brown spots appear at the base of the young stems close to the ground, gradually expanding, resulting in depression and contraction, and finally form a waist-shaped depression around the tender stem, which can lead to death or wilt. After the damage in the adult stage, brown spots appear on the leaves, and then fall off and perforate, and the cotton plants in the budding and flowering stage can also occur. After the stem is damaged in rainy years, dark-brown disease spots are formed at the base of the stem, and strips of woody fibers are exposed after the epidermis is broken. In severe cases, the stem breaks and dies, and sometimes tumor-like swelling can be formed at the affected part of the stem.

Anthrax: anthrax occurs in all the main cotton areas in China, and it is common in the Yangtze River valley. It is the main disease of seedling disease in southern cotton area. The damage of seedling and boll stage is more serious, and the growth of cotton seedlings is affected slightly. Serious pieces of dead seedlings, cotton boll damage caused by rotten bolls. The pathogen of anthracnose invaded the cottonseed when it began to germinate, which often caused the cottonseed to rot in the form of water stains after germinating in the soil, which could not be unearthed and died. After the seedlings were unearthed, the disease spots on the cotyledons were yellowish brown, the edges were reddish brown, and there were orange sticky substances on them, that is, the conidia of the pathogen. After the disease occurs at the base of the young stem, it produces a reddish-brown fusiform spot, then expands and turns brown, with a slight depression in the middle, and there is orange stickiness on the disease spot, which can wither the seedlings, and when the real leaf is killed, the primary small black spot becomes dark brown after enlargement. The edge of the round or irregular disease spot is purplish red, such as the dry climate is often cracked, the leaf is dilapidated, and the long reddish-brown disease spot can also be produced on the petiole and stem. The disease part is easy to break, and the surface of the disease spot produces reddish brown or orange sticky matter under wet conditions, that is, the conidia of bacteria. The disease spot on the bell is a dark red spot at first, then gradually expands and sinks, the middle becomes grayish brown, there is also orange sticky substance on it, and the disease bell rot can form a stiff flap.

Red rot: red rot, also known as root rot, occurs in all cotton areas in China. The occurrence rate of red rot at seedling stage in the Yellow River valley is the highest. The incidence rate is generally 20%, 50%, and the highest is more than 80%. The disease is serious in the seedling stage in the northern cotton area, and it can cause a large number of dead seedlings in the northern cotton area and serious in the boll stage in the southern cotton area. The red rot pathogen can do harm before the cotton seedlings are unearthed, making the ununearthed buds turn reddish brown and rot in the soil. After the unearthed seedling roots get sick, the root tip and lateral roots first turn yellow to brown rot, and then spread to the whole root, and can also develop to the ground part of the young stem. The seriously diseased seedlings withered, the disease spots are not sunken, and the thickening of the young stems and young roots above the soil is an important feature of the red rot disease, and then the disease changes to black-brown rot. In addition to invading the root and stem, red rot can also invade cotyledons, true leaves and cotton bolls. after the disease of cotyledons or true leaves, there are grayish red irregular or nearly round disease spots on the edge, which often break after the spot is enlarged, and pink mildew layer is produced on the surface when it is wet, that is, spores of pathogens, irregular shape of disease spots on cotton bolls, pink powder outside, and then often stick together to become pink lumps, serious disease bolls do not crack into rigid valves.

Quenching disease: quenching disease occurs in all cotton areas in China, especially in wet and rainy areas. it is a common cotton seedling root disease, which often causes cotton seedlings to wither and die, which has a great impact on cotton seedling growth. quenching disease generally starts from young fine roots, harms seedlings, and can also invade seeds and newly exposed buds into rotten seeds, rotten buds, so that seedlings are unearthed and stunted. When invading the seedlings, the symptoms of water stains initially appeared in the parts affixed to the ground at the base of the young stems, and in severe cases, they showed edema, expanded and yellowed, softened, and quickly rotted and lodged. Underground fine roots become yellowish brown, poor water absorption, resulting in the death of the whole seedling, cotyledons also fade, showing a water stain softening, in the case of high humidity, sometimes the disease part appears white flocs, that is, the hyphae of the bacteria. The difference between quenching disease and blight disease is that there is no brown sunken spot in the stem of cotton seedlings with quenching disease.

Black spot disease: black spot disease, also known as ring spot disease, occurs in all cotton areas in China. The northern cotton area is more serious than the southern cotton area, which can harm the roots, stems, leaves and young bolls of cotton. When the disease of cotton seedlings is serious, it causes a large area of dead seedlings. In recent years, with the increase of transgenic disease resistance area in China, black spot disease has become more and more serious year by year. From 2003 to 2004, black spot seriously occurred in a large area of the cotton area of the Yellow River basin, and the incidence rate was as high as 100%. In the serious area, all the leaves of the cotton field were killed at the beginning of September, and the whole field was pitch black. When black spot disease occurs in cotyledons or true leaves at seedling stage, the leaves first produce red-green spots, and then gradually expand into reddish-brown spots of 10-15 mm. The cotyledons of diseased seedlings often stick together, and there is a black mildew layer in the damaged pod shell. Injured cotyledons and true leaves are primary light yellow oil stains, small sunken spots on the back, and with the expansion of the disease spot, the edge is purplish red, nearly round or irregular, and there is no obvious concentric pattern. When the weather is wet, there is an obvious black mildew layer on the surface of the disease spot, that is, the conidia of the pathogen. Cotyledon petiole damage appears black-brown stripes, often resulting in cotyledon shedding, adult leaves damaged when the disease spot is mostly round or nearly round, and has concentric wheel pattern, which is the characteristic of black spot disease. The disease spot can be dry and cracked, when the disease is serious, the disease spot on the leaf can reach dozens, which makes the diseased leaf scorch and fall off, sometimes the petiole is damaged by yellow-brown stripe, and the petiole is often cut around the petiole, causing the cotyledon to dry and fall off into a light stalk. After the leaves and petioles die, the hyphae will spread to the cotyledon nodes, causing the stem tissue and even the growth point to blacken and die, and the immortal ones are also slow to grow, and the growth can stop for as long as 1 month.

Brown spot: Brown spot occurs in all cotton areas in China, especially in East China. Brown spot can occur in both seedling stage and later stage of cotton, but it mainly harms cotton seedlings. When the disease is serious, the cotton seedlings develop late and even the leaves die. Brown spot disease in the early stage of cotton seedlings, the cotyledons produce purplish red spots, when the weather is wet, the disease spots expand and synthesize irregular large spots, the edges are purplish red, slightly raised, and the middle is yellowish brown, which is scattered with small black spots, that is, the conidium of the pathogen. The disease spot is easy to break into perforation. When the damage is serious, the cotyledons fall early and the cotton seedlings die. The pathogen of brown spot did not invade the stem and growth point, and the diseased plant could still produce true leaves. When the true leaves were killed, the primary purple-red spots were born, and then gradually expanded into yellow-brown to grayish-brown edges with purplish red round spots, and the disease spots were brittle and easy to perforate. in severe cases, it can cause fallen leaves.

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