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Mistletoe


Mistletoe (pargacha) semiparasitic, angiospermic shrubs growing on the hosts with the help of modified roots (rarely terrestrial as Nuytsia in Australia). They are the members of the family Loranthaceae, distinguished by its parasitic habit, leathery leaves, cup-shaped receptacles, and inferior one-celled ovary. Seeds are surrounded by a persistent and very adhesive pulp, the viscin layer. In Bangla mistletoes are called 'pargacha'. They cause more economic loss than members of any other parasitic family of angiosperm. They mostly attack dicotyledonous and gymnospermous plants which include forest trees, horticultural plants and plants of aesthetic value. The effects of parasites on hosts are manifolds like reduction of vigour and growth rate, poor fruit and seed production; drying of tops; predisposition to other pests and diseases, and ultimately causing premature death.

Mistletoe

Birds play an important role in seed dissemination. When the birds eat the fruit, the adhesive pulp sticks to their feet and beak. The seeds are thus carried away and lodged in the twigs and branches of other trees where they germinate under favourable conditions and develop into bushes.

There occur about 15 mistletoe species under seven genera in Bangladesh. They are: Dendropthoe falcata (= Loranthus longiflorus), D. pentandra (= L. pentandrus), Helixanthera cylindrica (=L. heteranthus), H. ligustrina (= L. ligustrinus), H. parasitica (= L. pentapetatous), Macrosolen cochinchinensis (= L. ampullaceus), Scurrula gracilifolia (= L. scurrula var gracilifolia), S. parasitica (= L. scurrula), S. pulverulenta (= L. pulverulentus), Taxillus thelocarpa (= L. thelocarpus), T. umbellifer (= L. umbellifer), Tolypanthus involucratus (= L. involucratus), Viscum articulatum, V. monoicum and V. orientale.

In Bangladesh many important fruit trees like jackfruit, mango, and forest trees like sal, shegun, gamar, are attacked by mistletoes, which cause severe damage. Direct control measures of mistletoes include two methods: physical removal and chemical control. In physical removal the infected branches are cut. It is recommended to remove the parasitic bushes before they set fruits to avoid dispersal. The removal should be made at least 50 cm below the point of attachment of the mistletoe to the host to ensure the removal of the haustoria that extend up and down the branch. Chemical control mainly includes the sprays of 2,4-D and its derivatives. There are other chemicals also. Mixed plantations and other silvicultural operations are recommended for mistletoe control and management. [M Khairul Alam]