FOREST DISEASE MANAGEMENT

DISEASES OF Gmelina arborea :

Most of the diseases on G. arborea have been recorded from nurseries and plantations raised in different parts of the country. A brief description of various nursery diseases recorded in G. arborea is given below:

(a) Foot –rot:
            This is caused by Fusarium oxysporum. It has been recorded from Madhya Pradesh on 1-month old seedlings.
Symptoms:
            Infected portion exhibits water-soaked depression which late turns dark brown causing wilt and subsequent death of plants.

Control Measures:
            Soil drenching with 0.2% Bavistin or Dithane M-45 at monthly intervals effectively controls the disease (Jamaluddin et al., 1988).

(b) Poria root-rot:
            Poria rhizomorpha has been recorded as a root parasite of Gmelina arborea in part of India in north Bengal and Assam (Bagchee, 1953).
Symptoms:
            The severity of the disease has been noticed more on clayey sites where the soil becomes periodically waterlogged. The fungus perennates in the forest on woody debris in the soil and humus from which it spreads to the host through white coloured cord-like rhizomorphs often to a distance of 30 meteres, disseminating the disease from one tree to another. It causes brown cuboidal rot in the root resulting in death of root cambium followed by die back and death of affected trees both in natural regeneration and plantations. The sporophores of the fungus effused thin, brittle, poroid, crust, inseparable from the substrate, or white to pinkish cinnamon, pores round to angular, basidiospores hyaline, ellipsoid in shape.

(c) Root-rot and Collar rot:
            The diseases are caused by Sclerotium rolfsii and recorded in 1-2 months old seedlings in Kerala (Florence and Sankaran, 1987).
Symptoms:
            Paling of foliage and leaf shedding and subsequent death of the seedlings. In Kerala, the disease causes premature defoliation and is reported to be in mild form.

Control Measures:
            Soil drenching with 0.2% Bavistin or Dithane M-45 at monthly intervals effectively controls the disease.

(d) Leaf spot:
            Leaf spot is caused by Pseudocercospora ranjita and reported from Assam and Kerala. Deptoshaeria gmelinae causing leaf spot and die-back of twigs has been reported from Madhya Pradesh.  Other leaf spot fungi recorded from Madhya Pradesh are Phoma tropica, Alternaria laternata and Macrophomina phaseolina (Jamaluddin et al., 1988) and Corynespora cassicola is from Kerala (Sharma et al., 1985).
Symptoms:
            Paling of foliage and shedding of leaves are the common symptoms.

Control Measures:
            Application of Bavistin (0.1%) and Dithane M-45 (0.1%) are found effective against the diseases in nursery.

(e) Leaf and shoot blight:
            Colletotrichum state of Glomerella cingulata in association with Fusarium solani has been reported from Kerala causing severe blight disease in 5-6 month old seedlings during May and June.
Symptoms:
            The disease spreads rapidly after initial appearance in patches, causing large scale mortality of nursery stock. Infected plants exhibit blighting of shoots and leaves.  Subsequent colonization by Fusarium solani hastens blighting.

Control Measures:
            The disease has been effectively controlled by two applications of Bavistin at weekly interval (Sharma et al., 1985).

(f) Powdery Mildew:
            It is caused by Phyllactinia suffulta var. gmelina and recorded from Maharashtra.
Symptoms:
            The pathogen produces infection spots on the lower surface of the leaves with corresponding pale yellow colour on the upper surface (Patil, 1961).

(g) Phoma stem rot:
            Stem rot disease caused by Phoma nebulosa is recorded in 3-4 months old seedlings from Kerala (Sharma et al., 1985).  The disease flares up under warm and humid conditions especially in over crowded seedlings.
Symptoms:
            The infected seedlings wilt and eventually die.  Numerous pycnidia develop on dead stem, and spore masses ooze out from them on maturity. 

Control Measures:
            It can be effectively controlled by removing the affected seedlings from the seed beds, regulating the water to bare minimum and applying 2-3 foliar sprays of Dithane M-45 (0.05% a.i.) at weekly intervals.

(h) Canker disease:
            Stem canker disease caused by conidial state of Thyronectria pseudotricha and  Hendersonula toruloidea has been recorded from Kerala.
Symptoms:
            The pathogen causes depressions and necrosis of the bark on which numerous conidia (imperfect state) are produced resulting in formation of perennial cankers which increase in size due to fungal invasion to the surrounding healthy tissues. The bark later splits and peels-off exposing the dead wood (Sharma et al., 1985).

(i) Phomopsis Die back
            Twig blight caused by Phomopsis sp. and stem canker caused by P. gmelinae have been reported from Madhya Pradesh and Kerala respectively (Jamaluddin et al., 1988; Sankaran et al., 1987).