Damping - off
Description

   Among the different nursery diseases, damping-off is the most prevalent and highly destructive disease and it causes heavy loss of seedlings. It is referred to a group of diseases namely pre-emergence and post-emergence damping off depending on the stage of growth of seedlings when they are attacked. This disease is caused by different soil fungi such as Pythium, Phytophthora, Fusarium and Rhizoctonia of which the last two fungi are prevalent in forest nurseries in India.

Pre-disposing Factors
   High soil temperature, excessive soil moisture (water stagnation), high soil pH (alkaline), high nitrogen content, low light intensity due to shading, stiffy or clayey soil with poor drainage, dense sowing are the conditions which favor the disease development in serious proportion. Dark shade over the seedbeds and excess watering favoured the disease development.
Host Plants affected

   Acacias, Ailanthus, Albizias, Bamboos, Casuarinas, Eucalypts, Gmelina, Melia, Neem, Cadamba, Sandal, etc.

Causal Organisms

   Different soil fungi viz.,Pythium, Phytophthora, Fusarium and Rhizoctonia.

Symptoms

1. Poor seed germination.

2. Germinated seedlings show wilting and affected seedlings fall.

3. Symptom of the disease occur within two weeks of germination of seeds, when the first pair of leaves just emerges, and caused up to 60% mortality of seedlings.

4.The disease appears in the form of irregular patches in seedbeds. These patches enlarge rapidly from the periphery affecting the neighbouring, healthy seedlings under high soil moisture conditions.

5.Water-soaked lesions appear on the hypocotyls near the ground level. The lesions turn brown in colour and the affected portion gets damaged due to collapse of cells, resulting into a prominent constriction. The seedlings fall over the seedbed and eventually dies.

Control measures

The disease has been managed through:

a) cultural practices aimed at favoring plant growth and discouraging the growth of plant pathogen

b) use of chemicals like formalin and suitable fungicides. Formalin is applied as soil fumigant and the fungicides can be applied either as soil drench or soil mix.  Also, seed dressing with fungicide (Bavistin) in certain cases is found very effective.

c) Potting media should be properly sterilized by solar heating before use. 

d) Avoid excess watering and stagnation of water in the nursery beds.

e) Nursery beds should have proper drainage facility. 

f) Proper light and ventilation facilities should be provided in the nursery beds. 

g) Application of bio-control agents and bio-fertilizers (Trichoderma spp., Pseudomonas spp., VAM and Ectomycorrhizal fungal bio-fertilizers) to the potting mixtures before sowing seeds is advised.