DISEASES

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- 35o 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).
Last modified: Friday, 2 March 2012, 6:04 AM