FOREST DISEASE MANAGEMENT

DISEASES OF TEAK (Tectona grandis)

            Different disease problems of Teak were recorded in nursery.  The symptoms, causative organisms and their management are as follows:

(a) Leaf blight:
            This is caused by Rhizoctonia solani. 
Symptoms:
The infected plants show water soaked grayish brown patches that enlarge rapidly and cover a large part or the entire lamina.  The blighted leaves often show holes in the infected portion as a result of shedding of infected tissues during heavy rains.  The infected leaves dry up and are eventually shed.  The disease spreads laterally in the nursery through overlapping foliage of the adjoining seedlings often resulting in group blighting of seedlings.  In each case of severe infection, defoliation is high.

Control Measures:
Immediate removal of infected plants helps to prevent the disease spread. Application of Dithane M-45 (0.1%) is found effective in controlling disease.

(b) Leaf rust:
            This disease is caused by Olivea tectonae. 
Symptoms:
The infected leaves are almost plastered with yellowish brown fruit bodies of the fungus.  The upper leaf surface presents a grey appearance due to the formation of fleeks, which correspond to the position of sori on the lower surface.  Infected leaves fall off prematurely resulting in retardation of plant growth.  The disease is common in nursery and young plantations.

Control Measures:
The infected seedlings can be segregated and kept in isolation. Severely infected and dead seedlings can be burnt away from the nursery to prevent the spread of the disease. The disease may be controlled in the nursery by the application of sulphur based fungicide (Sulfax) on both sides of the leaves.

(c) Leaf spots:
            Leaf spot diseases are caused by different fungal and bacterial pathogens on teak.
Symptoms:
The symptoms are brown to greyish brown, which develop near the tip and along the margin of the leaves. The disease spreads laterally in the nursery through overlapping foliage of the adjoining seedlings often resulting in group blighting of seedlings.  In each case of severe infection, defoliation is high.

Control Measures:
Immediate removal of infected plants helps to prevent the disease spread.

(d) Powdery mildew:
            Members of the family Erysiphaceae have been recorded to cause mildews in teak. Phyllactinia corylea is recorded to attack teak laves (Bagchee, 1952). Phyllactinia guttata is also recorded to attack teak from other countries. Uncinula tectonae, widely occurs in nurseries and forests in central and southern India.
Symptoms:
            The fungus forms white powdery coating on the undersurface of teak leaves and later develops dark coloured cleistothesia over the white fungus weft (Spaulding, 1961). Uncinula tectonae is restricted to the upper leaf surface and the infected leaves are coated with a dull white mycelium and conidia borne on conidiophores. Conidia are air-borne which are produced abundantly and cause fresh infection. The metabolic changes in plants take place which lead to drying of infected leaves.

Control Measures:
            Sulphur dust was most effective in controlling powdery mildew in two year old seedlings followed by Baycor, Mortesan and Calixin (Kulkarni and Siddaramaiah, 1979).