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

BACTERIAL, VIRAL AND NEMATODE DISEASES

BACTERIAL DISEASES

• Several bacterial pathogens infest the foliage of nursery plants after their emergence from the soil surface.
• Sometimes bacterial spot (Xanthomonas campestris pv. vesicatoria (ex. Doidge) Vauterin et al. and canker (Clavibacter michiganensis pv. michiganensis (Smith) Davis et al.) in tomato and bell pepper and chili etc. and black rot (Xanthomonas campestris pv. campestris (Pammel) Dowson) in crucifers appear in nurseries and multiply rapidly.

Pathogen characters, disease cycle and epidemiology has been described in lecture No. 3 and 9.

Management

• Use of healthy seed.
• Dip the seed in Streptocycline (100 ppm) solution for 30 minutes.
• With the initiation of the disease spray the nursery beds with Streptocycline (100 ppm).

VIRAL DISEASES

• Several diseases like leaf curl and mosaics are of viral nature appear in the nurseries of some vegetables and carried from nursery to the fields.
• These viruses are transmitted through their insect vectors like aphids and white fly.
• To protect the nursery from these diseases, it is better to raise the nursery under a net house (40 mesh size) so that the nursery is not exposed to the viruliferous vectors.
• Insecticides Metasystox or Rogor (0.1%) should be applied at regular intervals to keep the vectors under check.
• Some insecticide dust like Malathion dust should be applied around the borders of the bed to restrict the entry of ants and other soil borne insects in the nursery.

Raising virus free vegetable seedlings:

• Leaf curl is a white fly transmitted viral disease, infestation starts from seedling stage and continue till harvest of the crop.
• The disease is specially seen in the tomato and sometime in chilli too and causes great loss of the crop.
• The leaves of affected plants show curling, mottling, rolling puckering etc. It can be controlled by the following ways:

Management

• Treat the soil of the nursery by carbofuran 3-5 g/m².
• Seed treatment with Imidachloprid @ 2.5 g/kg seed.
• Cover the seed bed after seed sowing by Agronet by making a tunnel like structure.
• Spray the nursery beds 15 days after seed germination at 7 days interval with Metasytox @ 1.5 ml/litre of water. Last spray is done 2 days before transplanting.
• Remove the infected plants if any in the field and buried in with soil or burn.

NEMATODE DISEASE(S)

• Invariably nurseries of tomato, brinjal and cucurbits raised in untreated soils are infested with nematodes like Meloidogyne spp. (Plate-2)
• Infested seedling if transplanted in field carry the nematodes to the fields where the problem does not exist earlier which may result in severe crop yield losses in later stages.
• Either treat nurseries with Formalin (5%) at least 20 days before sowing or with Carbofuran (5 g/m²) at the time of nursery bed preparation.