The government is stepping up monitoring of a disease thought to pose a serious threat to UK oak trees.
The problem is on the rise in England
Acute Oak Decline, which causes weeping patches on the stems of mature trees, is on the rise in England, particularly in the Midlands and the South East.
A national survey has been commissioned as part of a new £1.1m research drive.
Thousands of trees are thought to be affected, the Forestry Commission's lead scientist on the condition told Radio 4's Farming Today.
"This is a serious problem in the UK," said Dr Sandra Denman.
"So far we've only seen it in England, but because we haven't done any formal surveys we're unsure as to the full extent of the problem.
"But we do estimate that there are many thousands of trees that are affected."
Scientists believe a beetle may be responsible for the disease.
They are also trying to isolate and identify a bacteria found on the dying trees that might be linked to the infection.
Little is known about the rate of spread of the disease and whether all oak trees are at risk.
Comment: Watch here as a local attempts to measure the depth of the sinkhole... and runs out of line!