Tree Health Issues

Acute Oak Decline

There is a great deal of concern over this disease which was first recorded in 2002 in the UK; it has been likened to the devasting effect of Dutch Elm Disease in the 1970’s that has caused the death of millions of Elm trees.

The Oak trees affected by AOD are of the Sessile and Pendunculate species, those most vulnerable are aged over 50 years and located in the midlands and south of England. The symptoms are a bleeding from the trunk and branches, this is a dark sticky fluid that could be one of the means by which the disease spreads. In addition, the tree canopy gradually thins over a 3 to 5 year period as the disease develops. The weakened condition of the trees render them vulnerable to other pests including the wood boring larvae of the buprestid beetle. A range of other opportunistic pests and diseases continue to exploit the trees as the AOD develops.

The means by which the disease spreads is still open to debate by professional organisations such as DEFRA. The theories range from humans spreading the bacterium by waking around infected areas and then clean woodlands to the cause being squirrels, birds and even insects. Defra is funding research into AOD causes, distributions and scale of spread across the UK.

Management of Oaks with suspected or diagnosed AOD centres on the control of potential spread. If you suspect your Oak tree may have the disease as a qualified arborist for an inspection. A solitary Oak with this disease will probably be left in situ and just monitored for bleeding points and canopy thinning. In areas with other Oaks in the vicinity it may be necessary to fell the tree ensuring no timber or foliage is left as a mulch/woodchip or material is burned on site. The presence of AOD should be reported to the Tree Health Diagnostic and Advisory Team via DEFRA, replacement trees should not be in the Oak family.

Along with many others we really hope that the research under way does lead to a solution to this disease and ensure the mighty Oak remains an integral part of our British landscape.

Horse Chestnut Leaf Miner and Bleeding Canker

The Leaf Miner pest has been a problem to Horse Chestnut trees across Europe since the 1980’s but spread across the UK rapidly since the first recorded case in Wimbledon.

The Leaf Miner Moth (Cameraria ohridella) appear in the spring from pupae that have overwintered in foliage. After mating the females lay eggs on the leaves and as the larvae grow they turn the leaves brown as the dead patches spread.

As the leaves die back the ability of the tree to grow is inhibited as photosynthesis decreases. This weakens the tree and makes it susceptible to other pests and diseases.
Control of this pest focusses upon the application of pesticides to small trees but on the larger trees this is obviously not practical. Nature can do its part in the control such as birds predating on the moths. The best option is to collect and burn the fallen leaves to kill the pupae.

Bleeding canker has become a real problem since 2005. The pathogen for this is believed to be pseudomonas and phytophthora that cause bleeding lesions on the trunk and branches. These ooze a liquid that is usually black in colour which can then become sites for large fruiting bodies and bark separation. The Chestnut trees can recover if a callus develops over the wound, but where the cankers are widespread it may require branch removal to avoid hazards of fracturing and failure of limbs.

Seek professional advise if you are concerned.

Oak Processionary Moth

This pest has become a real problem in London and some of the home counties since its first invasion in 2005. The name derives from the habit of the hairy caterpillars moving around the Oak trees in a long line like a procession! It is believed to have arrived in the UK from nursery tree stocks in southern Europe where the problem originated.

The problems are primarily caused by the caterpillars eating Oak tree foliage and causing severe skin and eye irritation to any people coming into contact with the hairs on them. The health problems in some cases extend to sore throats and breathing difficulties, so it is well advised to avoid any contact with them. Where the foliage on an Oak tree is severely affected by the caterpillars the tree is weakened making it prone to several other pests and diseases.

Maps of the spread have been produced by the Forestry Commission. These maps show areas where they have been detected and treated in a core zone of invasion and an outer control and protected zone.

Identification

Lines of caterpillars in the summer months moving around Oak trees.
Silk looking hanging nests of varied sizes seen in the canopy on branches or the tree trunk.
The caterpillars each have long white hairs and shorter dark hairs.
Severe defoliation of the Oak tree leaves.
Changes to human health such as skin irritation.

What to do

Avoid any contact with the nests and caterpillars
Go to the Doctor with any suspected skin/eye/breathing problems
Report the tree to the Forestry Commission (www.forestry.gov.uk) and notify your council.
The larvae and nests need to be carefully removed by qualified arborists using a vacuum process to ensure no spread of the moths to other Oak trees.

The use of pheromone traps to catch the male moths has helped to eliminate OPM in core zone areas. The key solution is to stop a breeding population from being created. The actual caterpillars can be killed with suitable insecticides that ideally are sprayed in early spring just as they start to emerge from the larvae stage.

As tree surgeons our teams are trained to spot the nests and caterpillars to avoid both health problems to them and to control the spread of OPM. Our advice is to regularly inspect your Oak trees especially if you live in a core area.

R J Tree Services

A guide to tree fungi

We frequently come across concerns from customers over fungi found on or near garden trees

Fungi are a key component in recycling , they play an essential role in breaking down organic matter to produce nitrates and carbon dioxide that re enter the nutrient cycle to allow our biosphere to continue operating. Fungi are therefore not something unusual to see in your garden, they can come in a wide range of colours and forms for many people they can be seen as quite attractive.

In terms of trees the presence of fungal diseases can create a weakened and/or unstable form, so monitoring of the health of your trees is advised. The spores that cause these diseases are spread in a variety of forms including through the air, via insects and in dead leaves. Many fungi exploit the vascular system within the tree that move water and nutrients around, as they grow they extend root like threads (hyphae) into the wood; these fungi are hard to spot as they work within the tree. Other types of fungi grow fruiting bodies on damaged areas like snapped branches, rootplate areas or on leaves, as such these can be a little easier to spot and identify.

Tips to avoid active fungal activity.

Fungi love damp areas so try to avoid planting a tree in an area of waterlogged soils, most trees favour well drained soils.
Keep your tree in good health. Just like humans a good diet (regular fertiliser applications) and watering in dry months keeps your tree in tip top vitality and improves its chances to avoid fungal activity.
Remove dead and diseased limbs as soon as you observe them especially in the winter months, this slows the spread of fungi through the tree ( do ensure your pruning tools are cleaned after use to avoid spreading the diseases across trees).

Where leaves have been diseased we advise collecting them in the autumn and disposing of them away from your garden at council recycling depots or via incineration.

Fungicides

Many issues are raised over the use of watering or spraying fungicides to control the spread of fungal activity. Do ensure that you have correctly identified the fungus and apply the fungicide wearing appropriate protection for your eyes, lungs and exposed skin to avoid reactions and illness.

Honey fungus (Armillaria)

More than any other parasitic fungus this one is the most common one we encounter. They often grow in clumps as a yellow brown mushroom on the surface and white cream paper like sheets under the bark affecting many types of trees and shrubs including conifers, cedars, willow, birch, cotoneaster, plum, apple and cherry trees. The fungus can spread to surrounding trees via rhizomorphs (thread like strands) in the roots in some trees it may not kill the tree but it may weaken it so an inspection by qualified arborists is recommended.

Treatments are available such as Armillatox sprays several times a year around root collar areas but these cannot contend with large area infestations, the best option is to remove the tree and stump when a severe infestation is identified. The replacement trees or shrubs should have a good resistance to Honey fungus (eg. Yew ,Oak, Juniper, Laurel, Acacia, Beech and Ash).

Are your trees chocked with Ivy?

As tree surgeons we frequently come across trees that have a considerable amount of ivy in them. We need to balance the benefits of this bio diverse habitats with the hazards to the health and vitality of a tree.
Ivy in our gardens is usually the fast growing English Ivy (Hedera helix), this is a fast climber that can grow on the ground, on trunks and branches creating a dense mass with yellowish flowers and black coloured berries in the upper canopy. The ivy gains a foothold with root like growths on the stems to provide firm attachments to the tree bark, all nutrients and water are transported into the mass from the roots and as such it cannot therefore be called a parasitic plant.
The rate of growth of ivy often exceeds that of the tree itself. It is therefore inevitable that the tree can become completely subsumed by this voracious climber and may require some pruning back. The sheer weight of the ivy mass can cause the host limbs to fail and snap. As well as this hazard, where the ivy mass covers the canopy the tree leaves can be so deprived of light that reduced photosynthesis can occur and the tree will start to die back.

Managing tips for ivy control
The removal of ivy requires care as pulling sections from the tree can cause branches to snap or even bark separation creating points of entry for tree pests and diseases.
We recommend the use of “ringing” around the base of the tree, this will cause a rapid dieback of the ivy mass without causing problems from pulling the climbers from the branches. This work is best done outside the nesting season for birds to avoid unnecessary disturbance.
Where the aesthetic form of the tree requires removal of the ivy mass then a careful climbing operation is required, this is most frequently undergone on trees that have weakened limbs form the excessive weight of the ivy mass.

Chemical treatments such as Glyphosate are available to use on the ivy rootplate stems but this requires caution to avoid affecting the tree rootplate itself.

Ash dieback disease

The disease is caused by a fungus called Chalara fraxinea which has been tracked across Europe from Denmark through Germany, France and the Netherlands. The disease has wiped out 90% of the Ash trees in Denmark in just 7 years. When we consider that these trees make up around 30% of our native species it could have a real impact in the UK similar to the devastation caused by Dutch elm disease to Elm trees in the 1970’s.

The disease was first detected in tree nurseries from imported Ash trees arriving from EU countries. A ban on imports is now in place but it may be a little too late as the disease has been identified in Norfolk and Suffolk including on a wildlife trust site.

The disease has a number of symptoms for you to watch out for:-

Leaves wilt and turn a black brown colour.
Twigs and shoots dieback.
On the branches and trunk lens shaped lumps and black spots appear
The upper crown of the tree starts to die back
The tree develops growth on the lower braches to try and survive (epicormic growth)

There is uncertainty of how Chalara spreads from the obvious transmission via imports in nurseries to longer distance transmission via spores in the wind, insects and movement of infected timber.

We provide free advice on this disease if required.