John Dougan, the Forestry Commission's conservator in the area said:
"This is a worrying development and we are working with industry partners to manage its impact, both in terms of limiting its further spread and in dealing with the trees that have already been affected.
"There is a core area in Galloway Forest Park where it looks as if all larch has been infected and we are looking at how best to recover as much usable timber as possible.
"Beyond this core area, we are looking at taking further action to fell infected stands and those adjacent to it to try to minimise the further spread of the disease.
"Our aerial surveys have also identified suspicious sites in other parts of Scotland, however we think that the damage at these sites, most of which are well away from the main source of infection, could have been caused by canker - or reflects squirrel or deer damage of the tree.
"All of these sites will be visited so that our skilled surveyors can check for the disease."