Biological control

The basic principle of Biological Control is very simple, though there are practical ethical and legal problems with its introduction.  The most serious being the testing of any candidiate organism for its specificity, since once a species has been introduced it can be very difficult to 'unintroduce' it!  One must also consider the ethics of introducing further alien taxa, and also the unquantifiable effects on the ecosytem of such organsims. Supposing a caterpillar was introduced it might become a major food source for a particular bird species which may then become more successful with unknown consequences on the environment.  Nevertheless, there have been some very successful Biological Control programmes against alien plant taxa in other parts of the world. In Britain Japanese Knotweed was introduced without any of its natural predators and only a few of our native invertebrates will touch it.  Hence we get enormous monocultures of tall healthy plants which pour their resources annually, into an ever-increasing thicket of woody rhizomes just below the surface.  Systemic herbicides only kill part of these extensive systems, and may even encourage the germination of subterranean buds on the periphery of the rhizome network.  

In Japan it is unusual to find a Japanese Knotweed leaf that has not suffered invertebrate damage In Japan, all parts of the plant are exposed to invertebrate predation, canes and rhizomes suffer extensive damage from wood boring moth larvae

In Japan the woody rhizomes are commonly predated by the wood-boring larvae of the Japanese Swift mothIn contrast, in Japan all parts of Japanese knotweed, including the
rhizomes are under attack, and it is often difficult to find a single undamaged leaf.  It is also attacked by various fungi, with varying degrees of specificity.  As Japanese Knotweed in Britain is a single clone, and has no close relatives amongst our native flora and crop plants, it would be an ideal candidate for a Biological Control Programme.  Although there has never been a biological control programme against a plant pest in Britain, there is a lot of interest in producing one against Japanese Knotweed, and in September 2000 an expedition went to Japan to collect potential control agents.  These have undergone preliminary evaluation and we are currently awaiting the result of the next round of funding. For more information on the Biological Control programme visit The Japanese Knotweed Alliance.

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