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What is natural control?

Natural (or biological) control, is the use of living organisms to control pest populations.

Increasing trade and travel between countries has increased the number of plants and other non-native species arriving in the UK. The majority arrive without their natural enemies that keep them in check in their native range. In the case of plants almost all the insects, fungal pathogens or nematodes that would normally inflict damage on the plant are lost, giving the plant an unfair advantage over its new neighbours.

Natural control is a means of levelling the playing-field by re-introducing some of the specialist natural enemies that exert control on it in its native range.

A sustainable alternative

The use of self-replicating and co-evolved natural enemies for the long-term management of invasive alien species is a sustainable solution. Once established an effective agent provides control indefinitely without further cost or intervention.

Natural control has been used effectively against invasive species for over one hundred years.

What is known as the 'classical approach' is being proposed for Japanese knotweed. This method involves going back to where the invasive species originated (in this case Japan) and finding the natural enemies that keep the species in check.

Only after intensive research and vigorous safety testing to ensure this is specific to Japanese knotweed, will an agent be considered for release into the newly colonised area. In effect, this method utilises natures own in-built mechanisms to ensure equilibrium.

It is obviously important that potential control agents such as insects or pathogens don’t attack other plants, especially crops or endangered species. Scientists therefore spend considerable time (at least three years) studying the host range of any potential agent within a secure quarantine facility adhering to the International Code of Conduct.

This testing enables them to predict which, if any, other plant species might be at risk. Only once these stringent tests have been carried out to prove the natural control agent is safe, is an application for release made.

Find out more about natural control successes

Natural control - the advantages

Environmental – Natural control is exactly that – natural – and does not rely on the use of man-made chemicals that can impact adversely on the ecosystem in which they are used. Furthermore, the amount of herbicides required for weed control can be reduced.

Cost – After the initial research costs there is virtually no need for further expenditure once the agents are established and having an impact on the weed, bar monitoring activities.

Sustainability – It is permanent and therefore completely sustainable. The weed is continually under attack from an army of natural enemies.

Spread – The control agents, be they insects or pathogens will locate and affect most, if not all, populations of a weed until stopped by physical, environmental or chemical barriers, just as they have done in their native range.

Safety – Natural control agents should pose no threat to human health, crop production or beneficial organisms.

Landscape – Whilst the agents are doing their job on the Japanese knotweed, the native flora, which was previously out-competed, should be able to gradually recover and re-colonise areas without the need for extensive replanting.


Control not eradication – A successful agent should not eradicate the weed on which it depends, but should reduce it to acceptable levels. There may be costs associated with alternative control methods.

Timescale – It takes time. It can take five to ten years from release to achieve successful control.

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