Updated
April 2003

Several theories have been proposed as to why the Ragwort plague has happened.  Ragwort-UK believe that we have established the most probable reason for the plague and from this we have developed a solution to this invading nightmare:-

• The plague of Ragwort was not, in our opinion, brought about by changes in Verge Management as many have claimed, although the failure of MAFF to enforce its removal has doubtless worsened the problem.
   
• Nor was it caused by Global Warming bringing warmer summers, although conditions are certainly favourable for long seeding seasons.
  
  The simple cause of the plague of Ragwort, is that it has been growing for 13 years without effective control from its natural predator,    --    the caterpillar of the Cinnabar moth.

One Cinnabar caterpillar will eat a Ragwort flower in approximately 3 minutes. A brood of caterpillars will eat a whole plant in a day, they will then march off and find another plant, consuming over 30 plants during their life cycle. That’s nearly a million seeds consumed by the larvae from a single Cinnabar Moth.  A million seeds, that without predation have been finding their way into verges, banks, hedges, wasteland gardens and pastures, destined to become 10 million seeds the following year etc etc.

So why do we have a plague now?

The cause of the Ragwort plague started back in 1988.  That year was recorded in several places as
 ‘an exceptionally good year for Cinnabar caterpillars’.
 The caterpillars will normally only eat flowering Ragwort - that is, plants in their second year.  However, during the Cinnabar boom in 1988, the huge number of caterpillars consumed not only all of the flowering plants, but when these were gone, they went on to hunt out and eat all of the first year rosettes as well ……..

The effect the following year (1989) was that millions of Cinnabar moths emerged, but because the larvae consume only Ragwort and all the first year plants had been eaten the previous year, there were no food plants for the moths to lay eggs on. The moths live for only a few weeks after emergence, and during June 1989 many millions of moths died without being able to successfully lay eggs onto flowering Ragwort. 

Cinnabar only eat Ragwort, so --
in one short season, the Cinnabar moth population crashed in Britain.

Not so however for the Ragwort. Ragwort seeds remain viable in the ground for 7 - 20 years. Consequently a few plants grew from the seed stock to rosette stage during the Summer / Autumn of 1989. During 1990 these matured and seeded without any effective predation.  The tiny airborne seed spreads quickly and has continued unabated, colonising and building up soil seed reserves through to today.

Some Cinnabar moths survived or have occasionally blown over from the continent, but as our observations since 1996 have shown, the level of predation on the caterpillar, coupled with natural losses during pupation, can easily destroy a single moths offspring ‘in the wild’. This high loss rate is holding back the natural re-establishment of a strong population of Cinnabar, and a strong population is necessary to effectively control the huge levels of Ragwort that have now become established.

Without the return of the Cinnabar in sufficient numbers to effectively predate the present large reserves of Ragwort, the plague is continuing its invasion unabated and unattenuated.
Man has proven himself unable to master the task without help from the Cinnabar

Stopping the invasion