Leaf Blight
Causal organism: Alternaria spp.
- It is a weak parasite affects on older leaves.
Symptoms
- The infection starts with the minute dots on the leaf with irregular chlorotic areas on the tip portion of the leaves , then circular to oblong concentric black velvety rings appear in the chloroted area.
- Then the lesions develop towards the base of the leaf. Many spots coalesce and spread quickly to the entire leaf area leading to blight.
- Sometime a yellow hollow develops around each lesion.
- As disease advances, spot size increases and complete blightening takes place and leaves gradually die from the tip downward.
Mode of spread
- They spread mainly through air born spores.
- Prophylactic sprays with Mancozeb 0.25 % gives good control of the disease.
- Warm weather with humid condition caused by rain or heavy due helps in the spread of the disease and is favorable for the development of the conidia.
- Primary Source of Inoculum: Dormant mycelia,
- Secondary Source of Inoculum: Air borne conidia.
Epidemology
- The optimum Temperature for the development of disease is 28 to 320C
- Relative humidity is 85 to 90 %.
- Nutritionally poor soil, Susceptible host favours the disease.
Management
- Recommended NPK & FYM application.
- Use disease free planting material.
- The disease can be controlled by three foliar sprays with Mancozeb 0.25 %.
- Use of biological agents like Trichoderma viridae.
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Last modified: Thursday, 1 March 2012, 7:50 AM