Researchers now think ash dieback probably did not arrive on Dutch nursery stock as had been supposed,
Researchers investigated ash trees planted at six English sites over the past 20 years, comparing three in established areas of ash dieback in East Anglia, with three geographically isolated sites in Northumberland, Leicestershire and Devon.
The pathogen responsible for dieback, Hymenoscyphus fraxineus, was confirmed at all six, and some trees with typical H. fraxineus stem cankers had apparently died between 2001 and 2011, before the previous earliest UK records of the pathogen.
Cankers on dead trees were then tested for H. fraxineus using PCR-based detection, with pathogen presence confirmed as early as 2004/05 in some.
"This places H. fraxineus in England much earlier than previously thought, even pre-dating its documented arrival in neighbouring European countries," they conclude.
And they note that five of the six sites studied "were apparently stocked with ash plants from British nurseries and not from directly imported plants from mainland Europe where the disease is acknowledged to have been established for much longer".
The findings "suggest that planting of infected tree stock in England could date back to the early 1990s, with affected trees dying in the mid-2000s", they state.
However co-author and Forest Research principal pathologist Dr Joan Webber of told Horticulture Week she believed the findings "do not have any implications for disease management of ash dieback".
The results are published in the journal Forestry.