Biological control of weed

by Ikhsan hasibuan

weed is an unwanted plant that can be found on different ecosystem, there are in aquatic ecosystem, natural ecosystem and agricultural ecosystem. To control weed, it is better to know how a plant species developing into weed. Three stages of them are introduction of alien species, colonisation, and naturalisation. Introduction of alien species can be divided into two categories there are accidentally and consciously. When weed reproduce and maintenance of a local colony , it is known as colonisation and when it spreads dispersal widely and incorporation within the resident flora , it is called naturalisation. For this case, Cyperus esculentus and Hydrocotyle ranunculoides are good examples.

C. esculentus is an invasive weed, also known as yellow nutsedge or teki (Indonesian), that was accidentally introduced to Europe from the USA in early 1970's. This perennial weed is very hard to control since it has impurity in cormlets (bulbs) of gadiolus. It caused big damaged mainly on root-crop oriented agriculture. To limit its spreading, some legal measures should be done; farm hygiene for example obligation to clean farming equipment, zero-tolerance with regard to delivered produce, and ban on growing root crops such as potato or cassava.

H. ranunculoides or grote waternavel native from North America was introduced for the first time for use in garden ponts. Its fast growing and highly competitive characteristic threatens diversity by replacing other species. Controlling this species can be done by clearing of canals but it also needs high costs.

In Indonesia, Eichornia crassipes or water hyacinth or eceng gondok (Indonesian) was introduced from amazon river as ornamental plants. Nowadays, this plant makes big aquatic problem therefore links with eutrophication. Other weeds that have similar history are Opuntia cacti in Australia and Senecio jacobaea in Canada, USA and Australia.

Biological control for these weeds deliberate use of natural enemies and plant pathogens to reduce the population density of target plant species. It is also particularly relevant with invasive species that escaped from their natural enemies. For this, it needs to bring back weed's natural enemy through identification of enemies in the weed's native range and consecutive introduction as exotic control organism.

Cactoblastus cactorum was introduced from south America to control O. cacti in Australia. This insect had destroyed 90% of O. cacti eight years since it's first introduction. Neochetina eichornia and N. bruchi were natural enemies for E. crassipes introduced from South America. Caterpillar of Tyria jacobaeae can prevent generative reproduction of S. jacobaea.