Eucalyptus

Eucalyptus (2)

Among forest species eucalypt seedling is one of the most susceptible to termites. Eucalyptus seedlings upto about 1 year old are highly susceptible to attack by termites which feed on the roots. Investigations showed that the roots contained some substance which was attractive to termites. Extracts of the roots prepared in acetone and alcohol were found active as attractants in bioassay. Chemical characterization of the eucalypt root extract showed the active substance to be a phenolic acid.

Effective control of termites is usually achieved by long persistent synthetic pesticides like aldrin, chlordane or heptachlor. The possibility of replacing these chlorinated hydrocarbons by some non-insecticidal methods of control are mentioned below:

Termites cause serious damage to agricultural crops, forest trees, stored timber and other wood products. In most cases satisfatcory control of termites can be achieved with long persistent synthetic pesticides, provided the right chemical is used at the appropriate time. Among forest plantations, Eucalyptus spp. are attacked by termites during early stages of establishment, often causing considerable mortality. Field studies have shown that usually eucalypt seedlings below one year are attacked by termites. The mortality may be as high as 80%. The point of attack in general, is the living root system. Methods of control using cyclodiene insecticides have been standardised.

Search for pest control agents of natural origin has assumed greater importance in recent years due to the increasing cost of synthetic chemical pesticides and pollution problems. In addition, there are problems of outbreak of secondary pests and toxic effect on natural enemies of pests. In view of these problems several attempts have been made to control termites using alternative methods of control. These include use of attractant wood blocks together with a slow-acting termiticide, use of repellents or termite resistant materials and application of juvenile hormone analogues which can cause disturbance to the physiological or behavioural processes in insects. Known termite attractants include several constiruenrs of fungus-infected wood and lignin breakdown products. A sesquiterpenoid, isolated from fungus-infected wood was found to be attractive to the termite, Reticulitermes sp. Similarly extracts of the wood, Eucalyptus regnans was attractive to Nasuititermes spp. Controi of termites using a decayed wood block (which acted as an attractant) impregnated with a slow-acting insecticide to produce a toxic bait has been suggested. This method of bait blocks has been found useful in reducing the incidence of termites in buildings in residential areas in U. S. A. and Canada.

Eucalyptus is an Australian genus comprising of 140 species. They are evergreen species, all more or less aromatic and containing oil glands in their leaves. Mysore gum (Eucalyptus tereticornis), flooded gum (Eucalyptus grandis),blue gum (Eucalyptus globulus) and lemon-scented gum (Eucalyptus citriodora) are the important eucalyptus species grown in Kerala. Of these, Mysore gum and flooded gum are important timber species in the low- and mid-altitudinal zones of the state, respectively. The cultivation practices of these two species are described below. 

E. grandis grows best in deep, permanently moist, well-drained soils. E. tereticornis also prefers moist and well-drained soils such as loamy sands or alluvial loams, with high nutrient availability. A certain degree of salinity is tolerated, but strongly acid soils are ill suited. E. tereticornis adapts to a variety of sites, but responds poorly to excessively long dry periods. It is very easy to regenerate both species and they are good coppicers. The number of seeds per kilogram for E. grandis is 2.5 million, whereby roughly 630 viable seeds can be expected per gram. In the case of E. tereticornis one gram contains approximately 540 seeds.

 

Planting stock

Three-month-old containerized stock (polybag seedlings or root trainer seedlings) is recommended for planting. For seedling production, sow the seeds in seed tray in February. Trays should be kept moist with a fine spray of water until germination begins. Germination begins 7-9 days after sowing. The seedlings should be pricked out when they have two pairs of leaves into polybags of size 22 cm x 10 cm or root trainers. Planting stock of high yielding disease resistant clones are available at the KFRI / Kerala Forest Department nurseries.


Planting and stand management
Best time for planting is the beginning of rains. Planting is usually done in 20 cm x 20 cm x 20 cm pits (for clones use 30 cm cube pits) at 3 m x 3 m spacing. For production of pulpwood and fuel-wood, 6-10 year rotations are used without thinning. Depending on site conditions, E. grandis and E. tereticornis may respond to mineral fertilization with accelerated growth. Fertilizers may be applied at the rate of 30 g N, 30 g P2O5 and 15g K2O per sapling per year during the second, third and fourth years.


Injuries and protection

Polyphagous insects seem to attack the nursery stock. Quinalphos or malathion 0.05 per cent is recommended against them. Drenching the containers with chlorpyrifos is a preventive measure against termite attack in plantations. Quinalphos 0.05 per cent solution is recommended to control stem borer attack. 

Cylindrocladium leaf blight and pink diseases are common in eucalyptus trees. To control Cylindrocladium leaf blight, drench the nursery with carbendazim 0.05 per cent. Bordeaux paste is recommended against pink disease. Use disease tolerant clones for, preventing the incidence of both diseases.


Uses
E. grandis wood is pink to pale reddish brown in colour. It has good bending properties. It is used for housing construction, floors, furniture, crates, and veneers, in the paper industry and as fuel-wood. E. tereticornis produces dark red wood. It is hard, strong, tough, heavy, very durable and resistant to termite attack. It is used for a wide range of construction applications, suited for trench linings and fuel-wood. E. globulus and E. citriodora leaves are used for commercial production of Eucalyptus oil.

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