FOREST DISEASE MANAGEMENT
DISEASES OF SISSOO (Dalbergia sissoo)
Dalbergia sissoo is attacked by a number of diseases and the details are given below:
(a) Leaf spot:
Different fungi viz., Cercospora sissoo, Colletogloeum sissoo, Phyllachora dalbergiae, Phyllachora spissa, Phyllosticta sissoo, Mycosphaerella dalbergiae, Myrothesicum roridum and Alternaria alternata causing leaf spots on this tree species and recorded from the region this tree species grows.
Symptoms:
The pathogen, Cercospora sissoo attacks the leaves mostly on the lower surface, producing yellowish to grayish-green discoloration. Pustules are mostly intra-epidermal. Stomata are brown with simple or forked conidiophores (Sydow and Mitter, 1933).
The pathogen, Colletogloeum sissoo causes imperceptible leaf spots and is recorded from Varanasi, Uttar Pradesh (Pavgi and Singh, 1971).
The pathogen, Phyllachora dalbergiae attacks the upper leaf surface and produces shining black cushion-like stromata which may occur scattered or in clusters (Saccardo, 1883).
The pathogen, Phyllachora spissa attacks the leaves and forms densely aggregated dot-like dark stromata on irregular brownish infection spots and recorded from Wynaad, Kerala and Meghalaya (Bakshi, 1976); Khandala, Maharashtra (Ananthanarayanan, 1964).
The pathogen, Phyllosticta sissoo causes infection on leaves. The spots are round to irregular, greyish-brown which sometimes cover the entire leaf surface. Dark brown pycnidia are produced on lower leaf surface in densely aggregated groups (Saccardo, 1931).
The pathogen, Myrothecium roridum causes leaf spots in seedlings of sissoo from Bareilly and Dehra Dun (Uttar Pradesh) and Ambala (Haryana). Infection spots appear in June or eearly July. They are grey or light brown with dark brown margin on the concentric sones, coalescing to form larger leaf spots. The necrotic tissues usually fall off resulting in formation of shot holes (Tivari et al., 1991). The pathogen, Alternaria alternata appears in July continues throughout humid months and declines after September in Dehra Dun. The disease incidence is reported be as high as 100 per cent and almost 80-100 per cent leaflets are infected. Infection spots are dark brown, vary in size and shape and coalesce to form larger spots. The fungus sporualtes on the lower surface of the leaves. The heavily infected leaves are shed prematurely (Mehrotra, 1992a).
(b) Leaf Blight:
Rhizoctonia web blight of sissoo caused by R. solani an anamorph of Thanatephorus cucumeris was recorded from Dehra Dun (Mehrotra (1992b).
Symptoms:
The disease first appears on leaves close to the ground as water soaked grayish brown blotches which increase in size with the advancing fungal hyphae and ultimately the entire leaf blade is invaded by the fungus. The leaflets show stromatid aggregates on the under surface and eventually turn brown. The infected adjoining leaflets often join together by the fungal hyphae as if caught in a spider’s web hence the name web blight. Leaflets or entire leaf become detached prematurely but they remain clinging to the stem for a considerable period as they are invariably joined together by the fungal hyphae. There is a cluster of hyphae at the base of the petiole or petiole. The disease spreads laterally through contact of overlapping foliage of the adjoining seedlings resulting in group infection of seedlings in the nursery.
Control Measures:
The disease can be effectively managed through proper sanitation, weeding and foliar application of fungicide solution (Bayleton – 0.1% at fortnightly intervals).
(c) Powdery Mildew:
Phyllactinia dalbergiae causes powdery mildew on sissoo seedlings and recorded from Dehra Dun and Allahabad (Uttar Pradesh), Pusa (Bihar), Poona, Bombay and Nagpur (Maharashtra) and Chichrauli and Seonti (Haryana) (Pirozynski, 1965; Mukerji, 1969; Singh, 1973; Mehrotra, 1992c).
Symptoms:
The fungus produces yellowish, persistent, dense mycelium on the lower surface of sissoo leaves.
Control Measures:
Application of sulphur based fungicide was found most effective followed by Baycor, Mortesan and Calixin in controlling powdery mildew disease on D. sissoo seedlings in nursery.
(d) Rust disease
Maravalia achroa is recorded on seedling in nurseries from Uttar Pradesh, Bihar, Maharashtra and Assam (Patil and Thirumalachar, 1971; Bakshi, 1976; Mehrotra, 1987). The disease also occurs on young plantations but not in as severe form as in the nurseries.
Symptoms:
The disease appears in February-March on leaves and juvenile twigs and continues attacking the foliage and young twigs up to July-August. The infection declines following monsoon rains. The affected parts are killed resulting in die-back and subsequent death of affected seedlings. Uredinial sori are yellowish and formed on the lower surface of the leaves. Telia are colourless and pulvinate. The infected leaves are often deformed and the infected plants show perceptible retardation in growth and look stunted and weak. The disease incidence is recorded as high as 100% in the nursery at Dehra Dun.
Control Measures:
The disease may be effectively controlled by foliar application of 0.08% Bayleton at fortnightly intervals (Mehrotra and Pande, 1993).
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