If you suspect a juniper tree is infected with P. austrocedri, collect and submit samples of tree tissue for diagnosis.
When P. austrocedri attacks juniper trees the phloem (inner bark) turns from healthy white to orange-brown and may develop pockets of resin . You may wish to submit a sample to our Tree Health and Diagnostic Advisory Service to receive a firm diagnosis.
How to discover discoloured phloem
Select a juniper tree that is in the early to mid-stages of decline; dead trees with dead, bronzed foliage do not make suitable samples because the inner bark is too dry to yield P. austrocedri on isolation.
- Use a sharp knife to cut away the outer bark at the base of the main stem and upper roots to expose the phloem
- Look for signs of browning in the phloem, which indicates phloem death and a possible infection
- If you suspect an aerial infection, cut away the outer bark at the base of the affected branches to look for diseased, discoloured phloem
- If the phloem is infected, gradually work outwards to remove the bark until you reveal the ‘live-dead’ junction
The live-dead junction is often seen as an area of healthy white or pale pink phloem with ‘tongues’ of dull and diseased phloem extending into the area. Collect a sample of this material.
How to collect a sample
Cut away several 5-10cm2 sections of phloem that contain the live-dead junction and cut down to the wood underneath the phloem.
Alternatively, if the lesion margin cannot be identified on site, use a saw to cut away the entire section of stem or branch that contains the lesion margin. This section will have dead phloem at one end and live phloem at the other. Our diagnosticians can then find the lesion margin upon receiving the sample.
Figure 3 – Basal lesions on juniper infected with Phythophthora austrocedri. Outer bark has been cut away…
- Place samples in a sealable plastic bag and label with the sample location, date and contact details
- Mark ‘P. aust’ on the outside of the packaging
- Send samples immediately and by first class post (avoid posting on a Friday)
Samples from the north of the Mersey/Humber line go to:
Disease Diagnostic Advisory Service, Forest Research, Northern Research Station, Roslin, Midlothian, EH25 9SY
Samples from the south of the Mersey/Humber line go to:
Disease Diagnostic Advisory Service, Forest Research, Alice Holt Lodge, Farnham, Surrey, GU10 4LH EH25 9SY