Diseases of fruit plantation medicinal and aromatic crops (2+1)

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.