There are currently 339 sites across the UK infected with chalara ash dieback. On December 5, Forestry Commission Scotland (FCS) reported there were 26 sites north of the Border.
The Scottish total now stands at 39.
The 13 extra sites are a nursery that FCS has declined to identify, a second wider environment site near Eyemouth, and 11 newly planted sites.
The sites are located near Duns, Stobo and Kirk Yetholm in the Borders; High Valleyfield and Burntisland in Fife; Dunblane; Drumlamford House and Pinmore in South Ayrshire; Bridge of Allan; and Stranraer.
A spokesman for FCS said that while the increase may appear alarming, it was expected, and there were encouraging signs. He said there would be a tree health summit in March.
"We have said from the start there would be a steady increase in the known sites as surveys were completed, but the frequency of confirmations is definitely slowing down. It went from three or four a week in the two weeks given up to December 21, to six in four weeks since."
Meanwhile, the Tree Health Advisory Group, charged with developing a specific Scottish approach, had its first meeting on January 8.
The group, formed last month, is expected to report by April, before the disease becomes infectious again in the summer months. It comprises representatives from environmental, forestry and land-based industries.
One body involved is Woodland Trust Scotland. Its spokesman Rory Syme said: "Given the scale of FCS's search, it's not surprising that more cases of Chalara ash dieback have been confirmed in Scotland, and the rate of newly confirmed cases appears to be slowing down.
"The Woodland Trust Scotland is working within the Scottish Tree Health Advisory Group to help develop a control strategy for chalara ash dieback. This will be in place before the summer, when spores that are responsible for spreading the disease become active.
"It's really important that we don't unnecessarily fell mature ash trees, due to the role that they may have in resisting the disease, and because ash woods are a unique habitat that supports many important lichens and bryophytes.
"There needs to be close working between the Scottish and UK governments on pests and diseases that are affecting our native woodland. We also have to develop plans for controlling other pests and diseases that have the potential to enter the country in future."
Meanwhile, Owen Paterson, the UK Environment Secretary, has instructed that all imports of oak, ash, sweet chestnut and plane trees in future must have documents showing their origins, in a bid to save the UK's 80 million ash trees.
Mr Paterson said: "We need to ensure we have a healthy, thriving stock of our native trees and these controls will significantly help us to prevent pests and diseases from getting established in the first place.
"We have learnt from ash dieback how important it is to be able to act quickly to identify where infected trees may be.
"I want to make sure we can quickly trace and destroy diseased trees regardless of where they come from, as part of our effort to better protect our forests and woodlands."
Although there are only 12,355 acres of "pure" ash woodland in Scotland, compared to 1.63 million acres of largely conifer woodland managed by FCS (35% of Scotland's total woodland cover), the species is a significant component of our "mixed broadleaved" woodland.
I want to make sure we can quickly trace and destroy diseased trees regardless of where they come from