Spring into action with Plantlife: Ash dieback and lichens notes

Ash Tree along Abberd Brook, Calne

Dave Lamacraft (Plantlife) and Demelza Hyde (National Trust, Lydford Gorge) presented a lecture on Ash dieback and the lichens that rely on them. 

What lichens grow where:

• Climate and microclimate (Light, Temp, Humidity)
• Growth medium (Chemistry, Texture, Porosity)
• Environment (Nutrients, salinity, air pollution)

Elm trees and Dutch elm disease: Orange-fruited elm lichen required elm bark (PH7) and sensitive to pollution. This used to be a quite widely distributed lichen, however it is barely recorded since the 2000s. Similarly Eagle's claws lichen and sap-groove lichen have been hit hard with the loss of Elm. However, sap-groove lichen has faired better due to less Elm-specific requirements.

Why was Elm so important to so many species of lichen?

• pH - alkaline bark
• Rough texture and water retentive bark
• Big, long-lived tree that was widespread
• Tendency to acquire wounds that led to sap runs and wound tracks, which were a niche habitat for lichen.

Ash trees in Britain have over 100 species of lichen associated with them. This includes red list species, which historically were Elm specific species.

• Important for lichen due to being:
• Big, long-lived tree that was widespread
• High pH
• Poor resistance to fungal damage.

We are expecting around 80% loss of Ash in Britain, so what will happen to the lichen species that rely on Ash - what can we do?

Funding by Natural England and National Resources Wales has enabled Plantlife research into ways in which people can manage sites to mitigate impact from loss of Ash. One outcome was the publication: Ash dieback and Lichens in England, which you can download. This short publication looks at the risks and alternative species that could replace Ash as a host. In addition a list of particularly vulnerable lichen are assessed. This document, when followed can help land managers understand how to improve the situation before the Ash is lost - allowing species such as lichen to transfer to the new species or to prosper in dead wood that is left stacked.

We then moved onto a case study at Lydford Gorge, entitled Lichens, Ash Dieback and Lydford: Putting Theory into Practice.

Lydford is an SSSI temperate rainforest on the edge of Dartmoor with over 80,000 visitor each year, with ancient Hazel and Oak woodland on steep slopes. They now know that the 120 acre site is also important for lichens and bryophytes, when Tree Lungwort was discovered around 2019/2020. Since then a Rapid Woodland Assessment and a recording visit from the British Lichen Society has enabled a deeper understanding of the site and much data forming a foundation of knowledge.

Sadly, is has also been discovered that around 320 Ash trees need felling, with many other trees needing work. However, the new understanding has enable Demelza to create a plan for each tree, which has reduced the amount of trees needing to be felled immediately. This is allowing the NT to apply for a translocation licence to enable lichens to be moved to healthy trees.

An action plan was created with Plantlife to understand what the NT could do locally and nationally. This means that the Lydford Gorge team understand the trees that are important to their site and ensuring a favourable environment for those species, such as removing competition.

View the whole talk here:

Common spangle gall - Neuroterus quercusbaccarum

Symptoms: Develops on the underside of the leaves of pedunculate oak (Quercus robur) and sessile oak (Quercus petraea). The discs begin as yellow-green and age to become reddish.

Cause: Caused by a small gall wasp called Neuroterus quercusbaccarum. These galls are created when the wasps of the currant gall generation emerge and lay their eggs on the underside of the leaves. The offspring of these eggs will emerge around April and the cycle will begin again.

Control: There doesn't appear to be much stress on the tree, so can be left in place. Also there can be many galls on each tree, making it very difficult to keep under control.

Knopper (Acorn) Gall - Andricus quercuscalicis

Symptoms: The gall wasp (Andricus quercuscalicis) convert acorns into ridged structures. This process begins around September and the yellow-green galls age over time to become brown and drop off the tree.

Cause: Caused by a small gall wasp, which lays a single egg in each gall. This is a two-part process with the sexual generation developing galls on the catkins of the Turkey Oak in spring.

Control: While there were initial fears that this would impact the ability of the tree to reproduce, there doesn't seem to be any real issues and treatment is not required.

Oak Currant Gall - Neuroterus quercusbaccarum

Symptoms: Develops on the catkins and leaves of both pedunculate and sessile oak trees. There seem to be two stages, with the galls in the photographs being one stage and the spangle galls being another.

Cause: Caused by a small gall wasp.

Control: There doesn't appear to be much stress on the tree, so can be left in place. Also there can be many galls on each tree, making it very difficult to keep under control.

Thanks to OllieBeak at WAB for the help in IDing this gall. I found an ID guide from the NHM, available here as a PDF.

Spinach leaf miner - Pegomya hyoscyami

Symptoms: Damage to the spinach leaf as the larvae mine through the leaves creating a blister. The epidermis has been removed from one side of the leaf, in the top photo, to reveal the leaf miner.

Cause: Caused by a the spinach leaf miner. The fly emerges in spring, mates and lays eggs on the spinach leaves (as below). They eventually drop from the leaves into the soil to pupate - creating the next generation. There can be several generations each year.

Control: Stop the adults reaching the spinach by using covers. Keep the area weed-free. Rotate spinach, chard, and beet crops. Try using a Neem based spray which acts as a repellant and also slows the leafminers' ability to feed, interrupting the cycle. Advice on making neem spray can be found here - I don't know of its effectiveness.

Parasitic Plants

Mistletoe

Parasitic plants can get a bad name for themselves, in fact some of the most detested 'parasites' aren't parasites at all.

Take, for instance, ivy. Ivy often has a bad name because people thing that it's parasitic on trees and can kill them. Ivy isn't parasitic as it can photosynthesize and has it's feeding roots, that provide nutrients and water, in the ground. However, ivy does throw out 'roots' that provide the superglue-like adhesive that allow it to stick to the tree - or house! - to get it to a height where it can change from juvenile to adult. So it can be easy to make this mistake.

True parasites are either Holoparasites or Hemiparasites: 

• Hemiparasites contain little or no chlorophyll and therefore cannot photosynthesise. They reply completely on the host plant for nutrients, fixed carbon and water.  

• Hemiparasites can photosynthesise and therefore normally just rely on the host for water and nutrients.

They attach to their host either at the host's stem or root.

The parasitic mistletoe is a classic hemiparasite that attaches via the stem. In the UK mistletoes are now being encouraged due to worries that they may disappear from our landscape in the near future. They are commonly grown on trees in orchards, like the example below that was photographed at The Courts Gardens in Holt that is run by the National Trust. As mistletoe doesn't require too many resources, the tree isn't badly affected by the presence of the mistletoe and will do just fine.

Here's another example of mistletoe, this time in The Netherlands. Mistletoe seems much more common there than here - and is obviously abundant in the photo above. I have visited this part of The Netherlands over the past 28 years and always remember the balls of mistletoe in the area, which is testament to the ability of the trees to cope with this sort of parasite.













To the left is the hemiparasite, the purple toothwort. As you can see it has no leaves or other green parts and therefore has no chlorophyll to photosynthesise with and relies on the perennials that it parasitises, including trees, via their roots to survive.














Another example of a hemiparasite is the common broomrape. However, which this parasite attaches to the root of host plants, it parasitises plants similar in size to itself. While purple toothwort attaches to perennials such as trees, the common broomrape attaches itself to the roots of clover.
One can only imagine how many attachments it requires to nearby clover plants to throw up these impressive flower spikes.










It's easy to see why parasitism is an attractive way of live, in fact there are around 4000 species of parasitic plants identified to date. However if the parasite puts too much of a drain on the host, then when the host dies, it may die too. To combat this, root parasites can attach to the roots of many plants and will only be affected when wider environmental aspects come into play.

Oak Marble Gall - Andricus kollari

Symptoms: A hard, woody-like structure on the twigs of Oak trees. These often appear in clusters.

Cause: Caused by a small gall wasp.

Control: There are no chemical control methods for the Oak marble gall. There doesn't appear to be much stress on the tree, so can be left.

Apple Powdery Mildew

Symptoms: Young leaves breaking from buds which were infected during the previous year will show symptoms. Leaves are covered with a white growth.

Cause: This is caused by the fungus Podosphaera leucotricha. It overwinters in apple buds or on young stem growth - which can be seen as silvery white patches on the bark.

Control: Keep the plants well watered to prevent development. Mulch to preseve soil moisture. Prune out severely affected stems. Ensure the tree is pruned to ensure good air circulation.

Rose Black Spot

Symptoms: Black spots on leaves. They can be seperate or enlarge and join together. As seen in the photo, the leaves can turn yellow. They can also fall prematurely.

Cause: This is caused by the fugus Diplocarpon rosae. This seems to overwinter in the lesions on stems, bud scales and on fallen leaves.

Control: Dispose of infected leaves promptly. During spring prune out stems with lesions. Fungicide treatment is available, but if the infection isn't too bad then the plant isn't affected too much.

Acer Gall Mite - Aceria cephaloneus

Symptoms: The small red galls, shown in the photo to the left. They appear on the upper surface of the leaf.

Cause: Aceria cephaloneus mites suck the sap in the leaf, which induces the plant to react with the galls.

Control: There is no need to control this issue for the plant, as there is no harmful effect on the host. For small infestations the leaves can be removed, which will improve the look of the plant.

Cuckoo Spit

Symptoms: As in the photo to the left, white froth appears on the leaves, stem or flowers of many plants - here on lavender. This happens around early summer.

Cause: This is caused by the immature nymph stage of froghoppers. The froth protects and provides moisture of the immature nymphs. From mid-summer onwards they reach adult form and the froth will become less noticeable. More information on froghoppers here.

Control: Control is not normally necessary as the cuckoo spit is temporary and the plant can normally handle the amount of sap lost to the immature nymphs. If the nymphs are feeding at the tips of the plant, then remove by hand or accept that come distorted growth may occur.


One of the reasons that I like this blog is because of the readers. Lucy commented below about brushing aside the 'spit' to reveal the nymph. Naturally I had to rush out and do this. I was surprised at the size of it, nearly a centimetre long and brilliant green. Here's a photo. Thanks to Lucy - to visit her fab blog click here.

Lime Nail Gall Mite

Symptoms: The galls are around 5mm long as seen in the photographs and begin from late spring onwards. This occurs on the leaves of Lime trees, such as Common Lime.

Cause: is due to the chemicals secreted  while feeding on the underside of the leaf by a gall mite that is microscopic and goes by the name of Eriophyes tiliae. The galls are hollow and the mite lives within them during the summer.

Control: The mites don't have any harmful effects on the tree other than creating the galls. They can therefore be tolerated. In some ways, I find them quite interesting and exotic - however, I can see that some may not!