Leaf blight
Description

  It is one of the important diseases in nurseries, vegetative multiplication areas, seed and clonal orchards of many forestry tree species viz., Acacia, Albizia, Bamboos, Casuarina, Dalbergia, Eucalyptus, Gmelina, Melia, Neem, Cadamba, Pterocarpus, Sandal, Swietenia, Teak, Terminalia, etc.


Pre-disposing Factors
  After heavy rains, high humidity and temperature in nurseries and fields favors the disease development on the tender as well as mature leaf tissues.
Host Plants affected

   Many forestry species such as Acacia, Albizia, Bamboos, Casuarina, Dalbergia, Eucalyptus, Gmelina, Melia, Neem, Cadamba, Pterocarpus, Sandal, Swietenia, Teak, Terminalia, etc are affected by this disease.


Causal Organisms

   Different fungi like Alternaria, Cercospora, Colletotrichum, Curvularia, Cylindrocladium, Fusarium, Macrophomina, Phoma, Phomopsis, Pestalotiopsis, Phyllachora, Phyllosticta Pseudocercospora, etc. and bacteria viz., Xanthomonas and Pseudomonas are the causal organisms reported on many forestry crops.


Symptoms

1. Water soaked lesions on the tip of the leaves. Later, it spreads to leaf margin and finally the whole leaf loses its green colour.

2. The infected plants show water soaked grayish brown patches that enlarge rapidly and cover a large part or the entire lamina.

3. The infected leaves present a high blighted appearance and severely infected seedlings show premature defoliation.

4. The disease spreads rapidly after initial appearance in patches, causing large scale mortality of nursery stock.

5. Infected plants exhibit blighting of shoots and leaves and subsequent colonization by pathogens fasten blighting.

6. The blighted leaves often show holes in the infected portion as a result of shedding of infected tissues during heavy rains. 

7. The infected leaves dry up and are eventually shed. 

8. The disease spreads laterally in the nursery through overlapping foliage of the adjoining seedlings often resulting in group blighting of seedlings. 

9. In each case of severe infection, defoliation is high.


Control measures

The diseases can be managed by:

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

b) Severely infected plants need to be kept in isolation in order to prevent the spread of the disease to other healthy plants. 

c) Use of any one of fungicides like Bavistin, Blitox, Captof, Dithane M-45, Mancozeb at fortnightly intervals.