Diseases of Vegetable, Ornamental and Spice Crops (2+1)

SEPTORIA LEAF SPOT

Symptoms:

• Water soaked spots appear on the lower surface of leaf.
• Later these become more or less circular in outline and show definite brown coloured margins with grey centre (Plate-4).
• A few black glistening pinhead sized pycnidia may be seen in the center of spots.
• On stem, disease appears as small, slightly elongated, dark spots containing numerous black pycnidia.
• Black circular spots may also be seen on young as well as mature fruits.

Pathogen:

• The disease is incited by Septoria lycopersici Speg.
• On the host, young mycelium is hyaline, thin walled and sparingly septate.
• Pycnidia are subglobose, composed of 2-3 layers of brown cells.
• Pycnidiospores are filiform, slightly curved, hyaline and septate with pointed or rounded ends. No sexual stage has been reported.
• Two physiologic races have been identified.

Disease cycle and Epidemiology:

• The pathogen overwinters in infected plant debris in the form of mycelium or conidia or in debris of solanaceous weed hosts, such as horsenettle (Solanum carolinense L.) (Fig. 3.).
• The conidia are splashed by rain to the lower leaves of the plants.
• The spores produced in these pycnidia continue the secondary cycle of this disease.
• Temperature of 20-25^oC with 75-92 per cent relative humidity is congenial for disease development.

Management:

• Destruct infected plant debris and use of clean seed.
• One to two years crop rotation, trimming of lower leaves and staking of plants in case of indeterminate varieties/ hybrids have been found useful.
• With the initiation of the disease, spray the crop with carbendazim (0.1%) or mancozeb (0.25%) and repeat at 10 to 14 days interval.