Diseases of Fruit Plantation Medicinal and Aromatic Crops

Seedling die back

Causal organism: Phytophthora palmivora (Butler)

• Die back disease is severe on young seedlings during rainy season. It has been observed in the cocoa nurseries in Karnataka, Kerala & Tamilnadu.
Symptoms

• This disease is more severe on one month old cocoa seedlings though it is noticed in 1 to 4 month old seedlings.
• Infection may start from tip of the stem or cotyledon stalk or from the collar region.
• The disease appears as dark brown to black, water soaked and linear lesions.
• The lesions extend to leaves through the petiole resulting in wilting and subsequent defoliation of the seedlings.
• Defoliations and die back of the seedlings are noticed during advanced stages of the disease.
Etiology

• The mycelium is aseptate and 7 µm in diameter.
• Sporangiophores are simple or branched.
• Sporangia are inverted pear shaped terminal and zoospores is 8 to 10 µm in size.
• Oospores are spherical and measure 35 to 45 µm in diameter.
Source of inoculum

• Primary source of inoculum are the oospores and
• Secondary source are the zoospores and sporangia
Epidemiology

• Cool weather.
• Acidic pH
• Temperature of 18 to 25°C
Management

• All the infected seedlings in the nursery should be removed and destroyed.
• Disease can be controlled effectively by providing adequate drainage and soil drenching with Bordeaux mixture (1.0% )or copper oxychloride (0.3%).
• A combination of seed dressing & soil drenching with coccid at a concentration of 0.91 kg in 45 litre of water effectively controls the pre and post emergence seedling death.
• Application of bio- control agent Trichoderma viridae in the soil along with FYM @ .