FOREST DISEASE MANAGEMENT

DISEASES OF Albizia spp.
(a) Leaf spot and blight:
            Different pathogens such as Cercospora albizziae, Colletotrichum sp., Alternaria alternata, Camptomeris albizzia, Pleiochaeta setosa and Epicoccum sp. have recorded to attack of leaves of Albizia lebbeck in nurseries (Mehtrotra et al., 1992).  
Symptoms:
            The disease manifests on older leaves of seedlings as a small water soaked yellowish spot which later develops into a circular light brown lesion with a distinct yellowish margin. The spot hole develops in the advanced stages of infection causing premature defoliation.  The disease is aggravated under high humid conditions.  The tender shoots of seedlings are also infested and damaged.

Control measures:
            Application of Captaf (0.2%) fungicide solution as foliar spray is found effective in controlling the disease problem.

(b) Seedling wilt:
            It is caused by the fungal pathogen, Fusarium oxysporum.  
Symptoms:
            The lower leaves initially turn yellow and then fall off.  The yellowing proceeds towards the growing shoot and within a month the seedling dies.  The roots of affected seedlings get discoloured. 

Control Measures:
            Application of Dithane M-45 (0.3%) or Bavistin (0.2%) fungicidal solution is found effective in controlling the disease problems. Also, treating the seed beds with 0.2% Bavistin solution before sowing prevents the occurrence of disease pathogens.

(c) Rhizoctonia Leaf Web Blight
            It is caused by Rhizoctonia solani. The disease has been reported for the first time in Assam (Mehrotra, 1989; 1990). This disease was also reported on other broad leaved trees.
Symptoms:
            It first appears on leaves close to the ground, as water soaked silvery grey blotches.  The infected adjoining leaves become joined together by the fungal hyphae if caught in a spider’s web hence the name web blight. The fungal invasion of foliage is rapid over the wet leaf surface during rains (Mehrotra, 1990).

Control Measures:
            It can be managed through an integrated approach involving measures such as sanitation, cultural practices and use of fungicides.  Sanitary measures recommended are disposal of leaf litter by burning and segregation of diseased seedlings soon after such seedlings are spotted. This will help in preventing lateral spread of the disease through contact of the overlapping foliage of the adjoining seedlings thereby minimizing the disease incidence.  Cultural practices include raising of seedlings in poly bags instead of beds; keeping seedlings in lots of 250-300 seedlings instead of 1000 seedlings in nurseries. Application of Bayleton (0.1% a.i.) as foliar spray is found very effective in controlling the disease.

(d) Leaf Rust:
            It is caused by Ravenalia clemensiae. The pathogen attacks leaflets of the seedlings. Profuse development of pustules takes place on the leaf surface adversely affecting the metabolic activity of the plants resulting even in death.

Control Measures: 
            The disease is controlled by application of 0.2% Dithane M-45 or Sulfax fungicide.

(e) Little leaf disease:
            The disease caused by Pytoplasma like organisms is often observed in seedlings after the germination of seeds.  The cotyledons and first pair of leaves turn yellow.  Later, the foliage becomes bunchy with much reduced sized of leaves.