Although it only suffers from the effects of a few, do oak tree pests and diseases cause damage to the oak? Oak is famed for its natural resistance to pests and fungi, but like all living organisms it can still fall under attack. As a hardwood with a high natural tannin content, oak is unpalatable, if not actively toxic, to many species. European oak in particular has few parasites and pests, due to natural resistance of European species or unfavourable climatic conditions. Oak can suffer damage from fungi which live on the plant itself, or insects and their larvae which eat the wood.
Harmful Fungus Species
Damage from fungi is rarer than insect damage, mainly due to their longer life cycle. Oak tree fungus have an obvious physical presence and are therefore easier to spot and treat. Most oak fungus species only grow on live wood and will not affect sawn timber due to its low moisture content.
1. Beefsteak Fungus (Fistulina Hepatica)
This is a bracket type edible fungus with a bright red appearance similar to raw meat. Its main effect on the timber is a darkening of the wood grain, giving a tiger stripe effect. This is known as ‘Tiger Oak’ and its appearance can clash with existing oak features, making it undesirable for many projects. However it can be sought after by furniture makers who prefer the enhanced grain for aesthetic purposes in their products. This is actually a sign of Brown Rot developing in the heartwood and the presence of fruiting bodies should not be ignored.
2. Chicken Fungus (Laetiporus Sulphureus)
This is a bright yellow fungus that appears as brackets of overlapping frilly layers. It is also edible and mainly occurs on oak, but can affect other broadleaf species such as Robinia and Willow. Chicken fungus can cause aggressive Brown Rot in the heartwood as Hydrogen Peroxide it produces consumes the cellulose from the cells. The dry brown Lignin left behind can fracture into a cubical structure and eventually break down into powder. This destroys the heartwood, weakening the tree and leaving it prone to collapse.
3. Oak Polypore
Also known as Oak Bracket, this produces spongy brownish orange fruiting bodies that weep a honey coloured liquid. These appear towards the base of the trunk and roots and if left unchecked cause white rot in the root crown. White rot usually attacks the lignin and occasionally the cellulose in the wood, giving it a soft, spongy texture. This can weaken the roots and lead to collapse.
4. Dry Rot (Serpula Lacrymans)
If structural timber is exposed to damp conditions for extended periods, Dry Rot can take hold. Dried oak is usually resistant, but if its moisture content rises above 20% it can be affected. Dry Rot can spread strands across masonry and steel or even through porous plaster or mortar to infect timber. It produces fluffy white fruiting bodies with orange patches when mature and causes cubical rot, weakening timber. The only solution is the removal of affected material up to three feet away from infected areas. The source of dampness must be isolated and resolved to prevent any further reinfection.
5. Cellar Fungus (Coniophora Puteana)
This is similar to Dry Rot, affecting timber in damp, unventilated areas. However it can not spread across non porous materials. Cellar Fungus affects the structure of the wood in a similar way and must be treated identically to Dry Rot.
Harmful Insect Species
The most common types of oak tree pests are insect species, which, unlike fungi, attack trees and sawn timber. Each leave their own signs of infestation and though less noticeable than fungal attack, these can be used to combat their spread.
1. Powder Post Beetle (Lyctus Brunneus)
This species lay their eggs in the sapwood of timber with a sufficiently open grain to allow access. The main species affected are Oak, Sapele and Chestnut. Once the eggs hatch, the beetle larvae burrow their way out, consuming the sapwood as they go. This can take up to a year until they finally emerge as 3-4 mm long copper brown beetles between April and June. As they are tunnelling outwards and derive no nutrition from the heartwood, only the sapwood will be affected. Once the tunnels are detected, any infestation can be treated with appropriate solvent based preservatives. These are easily absorbed by the sapwood, making it poisonous to any larvae consuming it and killing the remainder.
2. Ambrosia Beetle (Platypus Cylindricus)
Ambrosia beetles can affect living or recently felled oak, tunnelling in and laying their eggs. They also introduce the Ambrosia fungus, which grows in the tunnels and provides a food source for the larvae over the next two years. However, the fungus cannot survive in timber with a moisture content below 25% and dies off as the oak dries. As a result, once the tunnels are detected the insects will have vacated the timber and no treatment is necessary. Ambrosia Beetle tunnels are 2-3 mm in diameter and are black due to discolouration from the fungus. They only occur in small isolated patches and have little aesthetic impact on affected timber.
3. Woodworm (Anobium Punctatum)
Also known as Furniture beetles, woodworm usually prefer softwoods but can affect oak. The adult females lay their eggs in cracks in the timber and as the larvae bore their way out they leave small tunnels along the grain of the wood. Woodworm larvae can take from three to five years to mature depending on the quality of food available. As a result, older furniture pieces may still contain larvae and care must be taken to prevent their introduction. Treatment with solvent based chemicals is usually effective but sterilisation or fumigation may be needed for more severe infestations.
4. Death Watch Beetle (Xestobium Rufovillosum)
These are around 7mm long when mature and prefer to feed on aged oak. They are most prevalent in old buildings, particularly in oak that has been weakened by damp and fungal infection. Death watch beetles lay their eggs in cracks and old tunnels created by other species. When the larvae hatch, they tunnel up and down the timber, feeding on the softened wood for up to two years. After they mature, they lay their own eggs and the cycle begins anew. The continued presence of the beetles and larvae can cause severe damage to already weaken timbers. The characteristic excreta, or ‘frass’ similar to round granules of sawdust are a clear indication of infestation. As they live in the core of the wood, Death Watch Beetle are notoriously difficult to remove. Professional gas fumigation is usually the only effective response.
5. Great Capricorn Beetle (Cerambyx Cerdo)
One of Europe’s largest beetles, these are normally a forest dwelling species that feed on dead and decaying logs. Occasionally, they will accidentally bore into fresh heartwood to lay their eggs. This can then be brought into sawmills and cut to expose alarmingly big tunnels, up to 18mm in width. Thankfully, this is a rare occurrence and an uncommon pest in fresh oak.
6. Oak Processional Moth (Thaumatopea Processionea)
This species of oak tree moth was first found in Britain in 2005, after being accidentally introduced from Europe. They have rapidly spread as an oak pest and are harmful to humans and animals. The caterpillars consume leaves from oak trees and can strip a whole tree bare in large numbers. This can leave trees vulnerable to other oak pests and diseases and affect their ability to photosynthesise. The Caterpillars are also covered in short hairs that contain an irritant called Thaumatopoein. Contact can cause itching, rashes, breathing difficulties and occasionally harmful allergic reactions. The Forestry Commission and the Animal & Plant Health Agency are currently attempting to eradicate this species from Britain.
A Hardwoods Group, we pride ourselves on the quality and standard of our timber. We only import our oak timber from trusted, reputable European sources. This guarantees consistency and quality in all the products we supply to our customers. If you have any questions about our range of products or how we can help you, contact us today.