Cotton

Corynespora Leaf Spot of Cotton

Corynespora cassiicola

Fungus

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In a Nutshell

  • Small brown circular spots on leaves.
  • Infected leaves drop prematurely.

Can also be found in

1 Crops
Cotton

Cotton

Symptoms

Symptoms first noticed on lower leaves of plants in early season. Then they spread up to the entire plant by the first month of plantation. Leaves initially show many small, dark red spots that turn brown with dark edges but typically retain their green or green‐yellow colour. Lesions are found on the boll buds and possibly on the bolls themselves. As spots age, they form light and dark brown rings. Possible 30 to 40% premature defoliation leading to yield reduction. Severely infected bolls lose quality and produce infected seed.

Recommendations

Organic Control

Bacillus thuringiensis is demonstrated to have biological control potential against Corynespora Leaf Spot of Cotton.

Chemical Control

Fungicides such as Carbendazim and Copper products can be applied between the first and sixth week of bloom. It is recommended to start at the 1st or 3rd week of bloom, with a possible second application at the 3rd or 5th week of bloom if needed. Alternatively, fungicides can be applied at the first sign of disease, followed by a second application if necessary. Another option is to apply fungicides at the first sign of defoliation, followed by a second application if required. However, it should be noted that controlling this disease with fungicides can be difficult if 25-30% of the leaves are already lost due to premature defoliation.

What caused it?

Moderate temperatures between 25°C and 30°C, high humidity, and prolonged leaf wetness from frequent rain, heavy dew, or fog promote infection and dissemination. Infestation is more severe in irrigated, strong-growing cotton with high yield potential.

Preventive Measures

  • Plant tolerant and resistant varieties.
  • Don't grow cotton and soybean in the same field for consecutive years.
  • Instead rotate your crops by planting maize, sorghum, or millet after cotton and soybean.

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