Cotton Disease & Management

1. Twig and Stem Blight of Cotton

Lasiodiplodia theobromae 

Symptoms 

• Dieback initiating from the twigs with multiple lesions coalescing together on the stem, resulting in the death of the branches. 
• Abundant, black, and solitary pycnidia were observed on symptomatic twigs.

Management

• Seed treatment is a pre-requisite. 
• Should maintain plant to plant and row to row distance.
• Should properly irrigate the field. Avoid excessive irrigation as it increases humidity that favors fungal growth.
• Use protectant spray if a favorable environment prevails for more than two days.
• Always keep in mind the wind direction while spraying the field.
• Spray the plant from head to bottom. 
• Following fungicides could be sprayed.

2. Asochyta blight 

Symptoms

• Brown or gray spots on leaves surrounded by a red halo; 
• Elongated red-purple cankers on stems cause the wilting and death of leaves above.

Management

• No fungicides are currently registered for use in cotton.
• Plough the crop debris into the soil after harvest.
• Crop rotation has little to no effect on control of the disease.

3. Cercospora leaf spot 

Symptoms

• Circular red lesions on leaves which enlarge and turn white or gray in the center
• Lesions often have a pattern of concentric rings and possess a red margin
• Dark gray spore masses form in the centers of the lesions making them appear dark gray.

Management

• Plough the crop residue into the soil to reduce inoculum levels
• Provide plants with adequate irrigation and nutrients
• Applications of appropriate foliar fungicides may be required on susceptible cultivars.

4. Fusarium wilt 

Symptoms

• Wilting of cotyledons and seedling leaves
• Cotyledons become chlorotic at the edges and then necrotic
• Older plants exhibit symptoms of wilting and leaf chlorosis
• Wilting is usually gradual but may be pronounced after a heavy summer rain
• If the infection is severe plants become stunted and may be killed
• The vascular system of infected plants becomes discolored and can be seen by cutting the stem.

Management

• Use the certified, disease-free seed
• Plant varieties with higher resistance to the disease in areas with a history of Fusarium diseases
• Fumigating the soil may reduce disease incidence.

5. Bacterial Blight of Cotton

Symptoms

• Attacks on all above-ground parts. 
• Spots on under the surface of cotyledons.
• On leaves, water-soaked spots firstly on the lower surface and then appear on both surfaces of the leaf. 
• Increase in size of spot and yellowing.
• Vein blight.
• Water-soaked lesions on bolls

Management

• Remove and destroy the plant debris.
• Use resistant varieties.
• Use acid delinted seeds.
• Treat the seed with a bacteriocide.
• Hot water treatment of seed at 56 oC for 10 minutes.

6. Cotton Leaf Curl Virus

Symptoms

• Leaf curling
• Darkened veins
• Vein swelling
• Cup-shaped leaf enation

Management

• The intensity of CLCuVD varies from locality to locality
• Vector control reduces CLCuVD infestation
• Seed dressing insecticides, yellow sticky traps, Adulticides / Nymphicides are effective tools to suppress whitefly.
• Resistant variety is the best solution