A road between the Rhondda and Cynon Valleys will be closed while Natural Resources Wales contractors carry out tree felling.
The road, from the Brynffynnon to Pleasant View, Llanwynno, will be closed from 26 February to 6 May.
A diversion will be put in place.
The operation is focused on the felling of larch trees in the nearby Forest, in response to the outbreak of Phytophthora ramorum, commonly known as larch disease.
The beech trees lining the road need to be felled as well, as they will become unstable following the removal of surrounding larch trees.
Due to the scale of the work to be undertaken, and its close proximity to the road, a full closure is the only suitable option to allow the work to be undertaken safely, and quickly.
A spokesperson from Natural Resources Wales said:
“We have to fell the beech trees lining the road as they will become unstable now they are exposed to the wind, following the removal of nearby larch.
“There is a risk that they could fall onto the road and cause an accident.
“The timber from the larch will be used in the production of fencing materials, paper, chip-board, biofuel, wood pallets or sawn into construction materials.
“The area will be left fallow for 18 months to 2 years, after which it will be replanted with a mixture of coniferous and native woodland species.”
Advice and guidance on how people can help reduce the spread of Phytophthora ramorum is available on NRW’s website.