General Plant Health Advice

For an interesting article by John Hammond on ‘Powdery mildew’ on subsection Cinnabarina, see the SRS yearbook no. 23, 2022.

Sirococcus tsugae

This was originally seen in the United States but first reported in the UK, including Scotland, in 2014 and 2015. It affects the genera Cedrus and Tsuga; cedars and hemlocks. Symptoms are severe shoot blight and defoliation. Dead needles have a characteristically pink colour and later go brown. There can be cankers and bleeding of resin from the bark. Spread is via rain splash and high winds. There is no effective control other than biosecurity and plant hygiene.

Marion Kinns, 2022

Stink Bug

Of less concern to us is a new Stink Bug originating from China and Japan. This has been highlighted by the RHS. The brown marmorated stink bug, Halyomorpha halys spread to the USA in the 1990s and is now found in various European countries. So far only adults have been discovered in the UK and no breeding populations.

They differ from native stink bugs with pale bands on the antennae, a row of pale dots on the body and a rectangular head. They appear to overwinter in houses.

The main threat is to orchards where a small number can cause great damage. Gardeners are asked to watch for them. If you find them, capture them and report suspects to or via the RHS gardening advice service

Marion Kinns, 04/02/22

Phytophthera pluvialis

Presently known to affect a variety of trees including western hemlock, tanoak, Douglas fir and various pines. It was first reported from Oregon, USA in2013 on tanoak ( Lithocarpus densiflorus) and Douglas fir and has been shown to be the causative pathogen in ‘red needle cast’ in radiata pine in NZ. It also causes shoot die back and lesions on stems, branches and roots.

It wasn’t seen in the U.K. until September 2021 in a Cornish woodland where it was found to be affecting mature western hemlock and Douglas fir. Further outbreaks have been found in Cornwall, Devon, Cumbria and near Loch Carron in Scotland. Wales reported their first outbreak in Dec2021.

Many members in our society will grow conifers so this fairly recent pathogen must be of concern. We have also seen how other Phytophtheras ( ramorum and kernoviae) affect a wide range of hosts including the genus Rhododendron.

Growers are asked to be alert to this disease and report any concerns via The TreeAlert online portal. Phytophthera pluvialis currently meets the criteria to be classified as a GB Quarantine pest for regulatory purposes.

Marion Kinns, 2022

UPDATE : 2024

Early investigations at various gardens have been encouraging in that there has been no sign of this particular fungal pathogen causing a problem in rhododendrons.

Marion Kinns,

Phytophthera austrocedri

This soil and water born fungus affects our native juniper which is already rare so there is some real cause for concern. It affects and damages roots leading to death. Discolouration of the foliage is seen which is either a uniform bronze following root damage or patchy from lesions on stems or branches. Tongue or flame shaped lesions up to 50cm can be seen under the bark and sometimes resin pockets. There is no natural resistance but plants on drier sites may survive.

Marion Kinns 04/02/22

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