Neem in India
Leaf web blight
It is a destructive disease caused by Rhizoctonia solani Kuhn, anamorph of Thanatephorus
cucumeris (Frank) Dank in neem and other forest nurseries. The disease first appears on the leaves
close to the ground as water soaked silvery blotches. The spots increase in size with the advancing
funga J hyphae and engulf the entire leaf blade; The leaves turn brown and get detached but remain
clinging to the stem for a considerably long ume as they are bound together by fungal hyphae
presenting a cob-web appearance. The pathogen also forms a loose sheath or weft of kind of
algaorfungus over the stem and branches, which is prominent during July-August. Later on, browning
of hyphae and their subsequent drying, however, makes them indistinguishable from the brown bark.
The disease is highly destructive and, in some cases, even cent percent plants are infected. Seedling
mortality as high as 70% has been recorded. The extent of defoliation varies from 30-100%. The
disease is most serious during mid-July to third week of August but continues upto October. Heavy
incessant rains for a couple of days followed by a prolonged cloudy weather (6-10 days) are ideal for
its spread. The pathogen is a soil inhabitant and causes infection along the stem when activated by
rains. Consequently, the bottom leaves are attacked first. Lateral spread of the disease is through
contact of overlapping foliage. The fungus alongwith the soil particles may also be lodged on the
lower plant parts by rain splashing.
It is a destructive disease caused by Rhizoctonia solani Kuhn, anamorph of Thanatephorus
cucumeris (Frank) Dank in neem and other forest nurseries. The disease first appears on the leaves
close to the ground as water soaked silvery blotches. The spots increase in size with the advancing
funga J hyphae and engulf the entire leaf blade; The leaves turn brown and get detached but remain
clinging to the stem for a considerably long ume as they are bound together by fungal hyphae
presenting a cob-web appearance. The pathogen also forms a loose sheath or weft of kind of
algaorfungus over the stem and branches, which is prominent during July-August. Later on, browning
of hyphae and their subsequent drying, however, makes them indistinguishable from the brown bark.
The disease is highly destructive and, in some cases, even cent percent plants are infected. Seedling
mortality as high as 70% has been recorded. The extent of defoliation varies from 30-100%. The
disease is most serious during mid-July to third week of August but continues upto October. Heavy
incessant rains for a couple of days followed by a prolonged cloudy weather (6-10 days) are ideal for
its spread. The pathogen is a soil inhabitant and causes infection along the stem when activated by
rains. Consequently, the bottom leaves are attacked first. Lateral spread of the disease is through
contact of overlapping foliage. The fungus alongwith the soil particles may also be lodged on the
lower plant parts by rain splashing.
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