A fungal-like pathogen known to affect a variety of tree species has been discovered on the Welsh Government Woodland Estate in Dyfi Forest, Gwynedd.
Phytophthora pluvialis can affect a variety of tree species, including western hemlock, Douglas fir and several pine species.
It is reported to cause needle cast - where needles turn brown and fall off - as well as shoot dieback and lesions on the stem, branches and roots.
It had already been discovered in parts of England and Scotland but this is the first confirmed case in Wales.
As the disease has never been detected in Europe before, research is ongoing to understand if other potentially susceptible species could become impacted.
This will help inform which control measures are appropriate and the potential impact this pathogen could have on the landscape and the forestry sector.
Climate Change Minister Julie James said:
We will continue to work with partner agencies across the UK to share information, experience and understanding to ensure a joint approach to monitoring and managing the situation.