Dothistroma needle blight currently affects Lodgepole and Corsican Pine trees in Scotland and has already jumped host to affect Scots Pine.
However, there are new worries about pitch canker, caused by the fungus Fusarium circinatum, to which the tree is also susceptible.
Passed either in seed form, on timber that has not had its bark removed or on infected plants, it has already spread from Spain to France.
"This is of massive concern," said Dr Steve Woodward, a reader in tree pathology at Aberdeen University and trustee of the Scottish Forestry Trust. "I think pitch canker is pretty likely to get here. It causes a lot of dieback and kills a lot of the trees it affects. So in terms of the outcome it could easily be as bad as the ash dieback."
Meanwhile, Portugal is currently battling a serious outbreak of pine wilt nematode, worms that infect pine trees and cause the pines to wilt. The blight spread from North American to China and Japan last century and is now present in Europe too.
"It was found fairly close to Lisbon and they're felling great swathes of pine there to try and slow down its spread but it has also appeared once or twice in Spain," said Dr Woodward. "I can't definitively say they would affect pines in Scotland but we don't want them."
He is now calling for tighter quarantine and sanitary controls, adding: "They won't stop things coming through, but they will mightily slow things down."
Scots pines were the largest and longest-living trees in the Caledonian Forest, the woodland habitat that once covered a massive area of the Highlands. Originally sprawling over 1,500,000 hectares, these native pinewoods now cover about 17,000 hectares but Scots Pine remains a "keystone" species and forms the backbone of the ecosystem in those areas. Pathogens affecting it would have a detrimental effect on those birds and mammals for which it is a natural habitat, such as the equally iconic capercaillie, the red squirrel, pine marten and wild cat.
Ash saplings at four newly planted Scottish woodlands had to be uprooted and burned as a precaution against the ash dieback that has affected 90% of ash trees in Denmark.
The sites were near Kilmalcolm, at Fochabers, at Carrbridge south of Inverness and at an unidentified south-east location.
On Friday, 150 staff from the Forestry Commission Scotland and the Scottish Government's plant health team began a round-the-clock survey of ash trees in the country's forests and woodlands.
Paul Wheelhouse, Environment and Climate Change Minister, said: "Currently we have just two confirmed cases of the disease in Scotland, but we expect that number to rise as the rapid survey progresses."
The call for action comes in the wake of reports about other ongoing breaches of Scotland's biosecurity. Earlier this year a fungal disease that attacks juniper trees, Phytophthora austrocedrae, was found in Perthshire, and the Forestry Commission Scotland has also recorded the presence of both Phytophthora lateralis, which kills Lawson cypress trees, and the pine tree lappet moth, which strips pines and other conifer trees.
Added to those are pests that have so far only been found in England but could spread northwards, such as the Horse Chestnut leaf miner moth and the Oak pinhole borer beetle. There are thought to be 15 imported diseases and pests attacking British trees, of which at least five are present in Scotland.
A spokesman for Forestry Commission Scotland spokesman said pitch canker was a known risk and that a pest risk assessment had been undertaken across Europe.
He added: "This resulted in emergency measures being introduced in 2007 preventing the movement of pine species and Douglas Fir, including seeds and cones, from areas where the disease is known to be present (Spain, Italy, France and Portugal.)
"Countries are also required to take annual surveys to determine the presence or absence of the disease, and this of course includes Scotland, where no sign of the disease has been found."