A review of dipterocarps - Center for International Forestry Research

Pests and Diseases of Dipterocarpaceae 123
not reduce the strength of timbers but degrades their
quality and value (Thapa 1971, Hong 1980a, b). Stains
can be caused by moulds, resulting in superficial staining
easily brushed or planed-off, and sap-staining fungi
(‘blue-stain’), producing deep penetration stains. The
most common are Diplodia spp., Ceratocystis spp. and
Lasiodiplodia [Botriodiplodia] theobromae (Supriana
1976, Hong 1980a, b, Charlempongse 1985). For
prevention and control of stain, it is best, when possible,
to process the felled timber within 1 to 2 weeks.
Otherwise, chemical treatment is the only way, and the
cut ends of logs should be immediately treated. The
chemicals most effective against black stain and mould
include the salts of chlorinated phenols (e.g. sodium salt
of pentachlorophenol, SPP), and organic mercury
compounds. These chemicals, effective against stains,
have a low efficiency on green moulds (Hong 1980a,
1981b).
Physiological Disorders
Very few studies have been conducted on physiological
disorders such as frost, drought, poor drainage and fire
damage, except in India on Shorea robusta (Davis 1948,
Ram-Prasad and Pandey 1987, Raynor et al. 1941,
Griffith 1945, Anon. 1947, Bagchee 1954).
A review of the adverse factors that probably combine
to cause serious dieback of Shorea robusta in Uttar
Pradesh (India) was made by Ram-Prasad and Jamaluddin
(1985) including deficient and erratic rainfall, low
retention of soil moisture, nutritional imbalance of the
soil, over-exploitation, unregulated grazing, fire and
excess of removal of fuelwood.
Mortality of Shorea robusta seedlings and young
saplings due to frost was mentioned (Davis 1948, Ram-
Prasad and Pandey 1987, Raynor et al. 1941 Griffith
1945, Anon. 1947, Bagchee 1954). Frost initiates canker
in advanced trees usually on the border of the forest
facing the open lands and on the banks of perennial
streams where the precipitation is heavy as dew or hoar
frost (Bagchee 1954). Radiation frosts, creating
frostholes by convection currents, kill saplings, create
cankers providing the route of entry for heart-rot fungi
and produce a moribund type of Shorea robusta which
ultimately becomes the object of attack by many
parasitic fungi and pests.
Drought is also an important cause of S. robusta
mortality (Pande 1956, Seth et al. 1960, Gupta 1961,
Ram-Prasad and Jamaluddin 1985, Khan et al. 1986). In
Malaysia, Tang and Chong (1979) have reported a
‘sudden’ mortality of Shorea curtisii seedlings due to
moisture stress. In India, Bagchee (1954) mentioned that
the roots of Shorea robusta must be in the region of
permanent water zone in order to be healthy. On the other
hand, Yadav and Mathur (1962) reported excess water
accumulation during the rainy season caused mortality
of S. robusta seedlings by development of white slimy
growth on the roots and Sharma et al. (1983) reported
deaths due to poor drainage.
Fire, often of anthropogenic origin, can damage S.
robusta (Joshi 1988, Ram-Prasad and Jamaluddin 1985,
Sinha 1957, Bagchee 1954, Bakshi 1957). It results in
deformity and other injuries to the immature trees such
as burrs, galls, tumourous knots, cankers, and heart-rot
fungi entering through wounds.
Management Aspects
There are few practical management methods directly
available to foresters against pests and diseases attacks
in mature dipterocarp trees. Concerning pests, the main
record is the ‘tree-trap’ technique set up in India for
reducing the population of Heterocerambyx spinicornis.
Regular surveys of insect populations in forest
plantations can help monitor the health conditions of the
trees, and some insect species (Buprestidae,
Bostrichidae, Cerambycidae, Scolytidae) are indicators
of sickly trees (Stebbing 1914, Beeson 1941). So forest
managers can identify which trees, providing shelters for
insect breeding, should be removed to avoid a massive
infestation of trees and logs. The infection by heart-rot
fungi on trees can be reduced by removing the dying and
dead trees and burning them. The danger is more
important if the tree bears fungal fruiting bodies and is a
source of infection (Bakshi 1956a, b). The well-known
technique of digging trenches around the infected areas
to isolate the infected roots and soil area can also be
applied.
Bakshi (1957) suggested lowering the felling age of
the trees in forests with a high incidence of heart-rot
and to avoid coppicing from infested stumps. Heart-rot
in the coppice standards due to Phellinus caryophylli
and P. fastuosus is transmitted by grafting healthy roots
with diseased ones or with decayed woody parts
embedded in the ground. The disposal of slash should be
a routine measure for protection of the stand against fire