Diseases of Vegetable, Ornamental and Spice Crops

DISEASES

A. FUNGAL DISEASES

1. CROWN ROT OR STEM ROT
Symptoms:

• The fungus attacks the leaves and flowers at the ground level and causes rotting which ultimately results in defoliation and toppling of spikes.
• Mycelia masses appear on leaf surface at or near the soil level.
• Soon the infected portion loose green colour due to rotting which extend and engulf whole leaf.
• The infected leaves fall down prematurely which results in the weakening of infected plant and such plants do not produce flowering shoots.

Pathogen:

• The disease is incited by Sclerotium rolfsii Sacc.
• The fungus has been is described in chapter Crossandra diseases.

Disease cycle and epidemiology:

• The fungus overwinters in the soil as sclerotia.
• Sclerotial germination is induced by volatiles that emanate from crop residues in the soil.
• Disease development is affected by high temperature and moisture, which favour sclerotial germination and optimum mycelial growth.
• Sclerotia germinate at 10- 35^o C, and the fungus requires > 99 per cent relative humidity.
• Sclerotial germination decreases with increased soil depth due to reduced aeration.

Management:

• The infection can be reduced by minimizing the moisture level of soil and destruction of plant debris.
• Follow long crop rotation.
• Solarize the soil atleast 40 days during summer months.
• Soil amendment with oil cakes (250g/m2) also reduces the disease.
• With the initiation of the disease, drench the plants with propineb (0.25%) and repeat at 10 to 14 days interval.

2. BORTYTIS SPOTS AND BLIGHT
Symptoms:

• On leaves, somewhat water-soaked, small to large spots appear with brown margins which become necrotic during dry conditions.

Pathogen:

• Botrytis elliptica (Berk.) Cook
• Conidia are aseptate, hyaline, botryose mostly 20-30 x 13-18 µm in size.

Disease cycle and Epidemiology:

• Pathogen perennates in the form of mycelium or sclerotia
• Warm humid weather favour the disease

Management:

• Spray plants with mancozeb (0.25%) or carbendazim (0.1%) or combi fungicides like Companion (0.25%).

3. LEAF SPOT
Symptoms:

• Water- soaked spots appear on the leaves which later turn elliptical or round brown. Later these spots coalesce together.

Pathogen:

• The fungus Fusarium equiseti (Corda) Sacc. is responsible for this disease.
• The mycelium of the fungus is septate and produces microconidia, macroconidia and chlamydospores.

Disease cycle and epidemiology:

• The fungus over winters in soil as chlamydospores.
• High soil temperature (25-28⁰C) favour the disease

Management: Spray / drench the crop with mancozeb (0.25%) and repeat at 10 days interval


B) BACTERIAL DISEASES

4. FLOWER BUD ROT
Symptoms:

• The disease is induced by bacterium mainly on young flower buds and results in dry rotting of buds with brown scorched, necrotic discolouration of peduncles.
• At later stage, bud shrivels and become dry.

Pathogen:

• The disease is caused by a bacterium Erwinia spp.

Disease cycle and Epidemiology:

• Disease spread is more in warm wet period

Management:

• Application of streptocycline (150 ppm) is recommended to control this malady.

Other diseases:

Viral diseases are incited by Tuberose Mild Mosaic Virus (TMMV).