Identification and Control of Main Diseases of Cotton

Liqun XU, Fenghua LIU, Lufeng KONG, Guofeng YANG, Wenji XU*

1. Dongming Hongya Family Farm, Dongming 274506, China; 2. Sanchunji Town People’s Government of Dongming County, Dongming 274506, China; 3. Xinjiang Xinluyuan Agricultural Technology Co., Ltd., Korla 841099, China

Abstract The main symptoms of cotton viral diseases, bacterial diseases, fungal diseases and physiological diseases are introduced, and the corresponding prevention and control techniques are put forward, in order to provide a certain basis for the improvement of cotton yield and quality.

Key words Disease control; Main diseases of cotton; Viral disease; Bacterial disease; Fungal disease; Physiological disease

1 Introduction

Cotton has been one of the major cash crops cultivated in China since the 1980s, and it was mainly cultivated in the Huang-Huai River basin and the Yangtze River basin at that time. In recent years, due to various field factors and other influences, China’s cotton planting area has migrated to Xinjiang, and the planting area in the hinterland of China has been greatly reduced. But no matter where cotton is grown, disease has always been a top priority in cotton management. It is an important factor to ensure cotton yield and quality by effectively doing a good job of cotton disease control. The paper gives a brief introduction to the prevention and control techniques of main cotton diseases, hoping to bring some reference to readers.

2 Main diseases

2.1 Viral diseasesThe viral diseases of cotton mainly include lobular virus, mosaic virus,etc.

2.1.1Damage symptoms. The affected plants are dwarfed obviously, with smaller and shriveled leaves, shortened and deformed internodes, and there are obvious yellow and green mottled leaves. Some green mottled leaves are restricted by veins and some turn red, and the symptoms are more obvious in old leaves.

2.1.2Main transmission route. Common mosaic virus is mainly transmitted by tobacco whitefly. Tobacco whitefly feeds on veneniferous weeds and transmits the virus to cotton plants through mouthparts, causing sporadic disease.

2.1.3Control methods. Piercing-sucking pests such as tobacco whitefly, thrips and aphids are the major objects for the prevention of cotton viral diseases, so as to reduce the source of infection. After the onset, brassicin can be sprayed with monopotassium phosphate to reduce the harm.

2.2 Bacterial diseasesThe main bacterial diseases of cotton include bacterial angular leaf spot, bacterial boll rot,etc.

2.2.1Cotton angular leaf spot. Cotton angular leaf spot can occur in the whole growth period of cotton, and the bacterium can harm seed buds, cotyledon, true leaves, stems, bolls, bracts and other parts of cotton. Seed rot and bud rot will easily occur after seeding of seeds with bacteria. Water-soaked small round spots will appear in cotton plants in the early stage of damage, and then expand into irregular or polygonal spots. The lesions on the leaves are translucent to light and spread along the veins, forming black brown strip lesions. Cotton is susceptible to angular leaf spot at high temperature and humidity, and the disease will aggravate after rainfall.

In the initial stage of incidence, copper phytate can be sprayed or the mixture of agricultural streptomycin, compound sodium nitrophenolate·naphthylacetic acid, and monopotassium phosphate can be sprayed, to reduce the harm.

2.2.2Cotton bacterial boll rot. Brown necrotic bands appear on the surface of immature bolls along the longitudinal groove line, and part or all of the immature cotton fibers inside the boll turn brown and become water-soaked. In severe cases, the whole boll turns brown and the shell becomes soft, or the boll cracks early and can not mature normally.

Excessive humidity should be avoided in the boll setting stage of cotton, and light and plant ventilation should be increased.

2.3 Fungal diseasesThe main fungal diseases of cotton mainly includeColletotrichumgossypii,Mycosphaerellagossypina,Rhizoctoniasolani,Pythiumaphanidermatum,Leveillulamalvacearum,Fusariumoxysporum,Verticilliumdahliae,Fusariummoniliforme,Phytophthoraboehmeriae,etc.

2.3.1C.gossypii.C.gossypiioccurs at all growth stages of cotton, especially at the seedling and boll stage. The onset at the seedling stage will cause seedling blight, and that at the adult stage will cause rotten boll of cotton.C.gossypiiis likely to occur in case of low temperature and much rainy in the seedling stage and high temperature and much rainy in the boll stage. Extensive management, poor field ventilation, many years of continuous cropping and high soil moisture easily lead to the incidence ofC.gossypii.

In the initial stage of incidence, kresoxim-methyl, thiram, tebuconazole and pyraclostrobin can be sprayed alternatively.

2.3.2M.gossypina.M.gossypinamainly harms cotton leaves, and will produce mildew layer when it is wet, affecting the photosynthesis and normal physiological function of cotton, or leading to plant wilt and death in severe cases. Low temperature, high humidity and weak growth are beneficial to the occurrence ofM.gossypina, and sand loam soil is more susceptible to the disease than clay.

In the initial stage of incidence, tebuconazole, difenoconazole and pyraclostrobin can be sprayed alternatively.

2.3.3R.solani.R.solaniis a major disease of cotton at the seedling stage, also known as root rot and black root disease. After cotton seedlings are unearthed, the symptoms first appear at the base of young stem near the ground. Initially, yellow-brown spots appear, then gradually expand, sunk and decay, which will extend to the periphery of the stem in severe cases. The depression area is wasplike due to excessive water loss, and finally turns black brown, leading to death and non-lodging of cotton seedlings. Continuous cropping, low-lying poor drainage, excessive soil moisture, low soil temperature and poor ventilation easily lead to the incidence ofR.solani.

In the initial stage of incidence, difenoconazole, hymexazol·metalaxyl and hymexazol·ethylicin can be sprayed alternatively.

2.3.4P.aphanidermatum.P.aphanidermatumis a common root disease of cotton seedling. Low temperature and high humidity, high temperature and high humidity easily lead to the incidence, and the disease often causes cotton seedling to wither and die in large area. After cotton seedlings are unearthed, they are susceptible to the disease in case of low temperature and rainfall.

The moisture in the field should be concerned. In the initial stage of incidence, metalaxyl and propamocarb can be sprayed alternatively.

2.3.5L.malvacearum. There are polygonal disease spots on both sides of the leaves, and thick white powdery mildew layers on the leaves. In the late stage, small black brown dots are produced in the powdery mildew layers. High temperature, drought and large temperature difference between day and night are conducive to the occurrence of the disease.

In the initial stage of incidence, flusilazole, difenoconazole, azoxystrobin and prochloraz can be sprayed alternatively.

2.3.6F.oxysporum. Diseased cotton plants are withered, with sparse bolls and reduced boll weight, resulting serous yield reduction of cotton and reduced fiber quality. Low-lying cotton field, extensive preparation, poor drainage, large soil moisture, high humidity and low temperature easily lead to the incidence ofL.malvacearum.L.malvacearumof cotton mainly has the following symptoms.

(i) Yellow reticulate type. Except for chlorosis of leaf vein, degreening and yellowing of seedling cotyledon or true leaves, the mesophyll remains green, and the leaf blade partly or completely reticulate. Finally, the leaves wither, dry and fall off, and the plant dies.

(ii) Yellow type. Cotyledons or true leaves begin to turn yellow from the tip or margin of the leaf, and the yellowing gradually expands inward and finally causes leaf shedding.

(iii) Withered type. The cotyledon or true leaf of the sick plant suddenly lose water, with the leaf color becoming dark green and the leaves becoming soft and drooping. Finally, the whole plant droops and becomes green wilting.

(iv) Purple red type. When the temperature is low and unstable in early spring, the cotyledon or true leaf of cotton plant becomes purple red partially or completely. As the disease progresses, the leaves wilt and fall off, and the plant dies.

In the initial stage of incidence, trichloroisocyanuric acid, humic acid copper and chloroisobromine cyanuric acid can be sprayed alternatively.

2.3.7V.dahliae. The disease occurs when cotton seedlings grow 4-5 true leaves. The flower bud stage is the appropriate stage of the disease that will develop rapidly. Low temperature and high humidity easily lead to the incidence ofF.oxysporum. The main symptoms are as follows.

(i) Defoliating type. Leaf veins or leaf margin suddenly appear chlorotic wilting, and sick leaves turn from light yellow to yellowish brown rapidly. Apical tip of lateral branch of main stem of the diseased plant become brown and die. Diseased bolls and bracts become brown and dry, while buds, flowers and bolls fall off in large numbers.

(ii) Yellow spot type. Yellow patches appear on the leaves, which then expand into palmately yellow stripes, and the leaves do not fall off. Vascular bundles turn pale brown when the stem is opened, which is an acute symptom ofF.oxysporumof cotton.

(iii) Withered spot type. The leaves are featured by local withered spot, which finally wither and fall off.

In the initial stage of incidence, trichloroisocyanuric acid, humic acid copper and chloroisobromine cyanuric acid can be sprayed alternatively.

2.3.8F.moniliforme. At the seedling stage, the roots and lateral roots of infected cotton seedlings turn yellow, and then turn black brown and rot. When the young stem is infected, the ducts turn dark brown, and yellow streaks appear near the base of young stem, which then turn brown and rot. The young roots and stems are swollen, and irregular gray-red spots are produced in the margin of cotyledon and true leaves. When the humidity is high, it produces pink mildew layer. The stem base is susceptible to the disease at the adult stage, producing ring or local brown scars, with corroded cortex and yellowish brown xylem. When cotton bolls are infected, amorphous disease spots are produced in the initial stage. In case of wet weather or continuous rain, the disease expands rapidly throughout the whole boll, producing uniform pink or light red mildew layer, which will easily adhere together after rain and become pink lumps. As a result, the disease bolls can not crack, and cotton fibers decay into stiff flaps. When seeds are infected, the germination rate decreases. The disease is severe under the condition of low temperature and humidity, much rainfall and less sunshine.

In the initial stage of incidence, hymexazol, carbendazim and Bordeaux mixture can be sprayed alternatively.

2.3.9P.boehmeriae. At the seedling stage, the root and the base of the stem are reddish-brown striped, and then the lesion wraps around the stem, while the root and the base of the stem are necrotic. At the boll stage, the disease usually occurs on the boll of the middle and lower fruit branches of cotton plant, generating light brown, light green to black water-soaked lesions in the initial stage. The bolls are easy to rot or fall off in cause of much rainfall and humidity, and some become stiff bolls.P.boehmeriaeoccurs early and seriously in case of vigorous growth and continuous rainfall. In the growing period of cotton boll, sufficient light, high temperature and less rain can reduce the occurrence ofP.boehmeriae.

In the initial stage of incidence, mancozeb and metalaxyl can be sprayed alternatively.

2.4 Physiological diseasesRed leaf blight is a physiological disease caused by deficiency of phosphorus and potassium fertilizer in cotton. In addition, chlorosis, yellowing or whiting leaves, shortened internode and slow growth are usually caused by the lack of manganese, iron, calcium, sulfur, copper, zinc and other elements. In severe cases, the leaf blade becomes smaller and the leaf margin turns upward. Eventually, the leaves are wilted.

Trace elements should be supplemented in time. Cotton is a potassium-preferred crop, and appropriate application of monopotassium phosphate in late period can effectively alleviate the occurrence of red leaf blight.

3 Conclusions

Cotton plays a vital role in the economic development of China’s agriculture, while cotton diseases will cause serious adverse effects on the growth of cotton. In order to improve the yield and quality of cotton, cotton growers must take scientific management according to the local actual situation and planting habits, and take effective prevention and control measures to control cotton diseases, to ensure the yield and quality of cotton, as well as the economic benefits of farmers.