Culling greys would go a long way to cancelling the spread of the disease for sure (% of the greys tested in one area were found to be carrying the disease), but halting it altogether is another matter. The problem is, once the virus gets amongst the reds it rapidly spreads throughout that particular area. In the Cumbria area, the rate of expansion of grey squirrels over the last decade is 100km2 per year. The decline of the red squirrel is about 70- km2 per year. There is about a 3 year time lag between grey squirrels arriving in an area and the poxvirus occurring in red squirrels.
So