The arboricultural information notes give general information on a number of tree-related issues, from maintenance to an appreciation of associated wildlife. They are not specialist papers.
We hope the information will encourage you to research further into subjects that prove of interest by using books, the internet and practical visits to parks, woodland and the wider countryside.
This series of information notes will be added to periodically. Any suggestions for subjects you would like included would be welcomed for consideration.
1. Consider what you wish the tree to provide – shade, blossom, berries for winter bird feed, colour or leaf shape may aid your final selection.
2. Consider the ultimate height and spread of your selection and assess any future problems against the location chosen.
3. Check that the tree is compatible with local soil conditions.
4. Purchase your tree from a reputable supplier at a size that you can safely lift and plant. Also purchase one or two tree stakes, depending on the size of your tree, together with protective pads to prevent the tree rubbing against the stake, and plastic or rubberised strapping to use as ties. You will also require a few galvanised nails and a hammer.
5. Purchase your tree in good time to allow planting from November to February. Delay any planting if the ground is waterlogged or frozen.
6. If your selected tree is not root-balled, containerised or potted, ensure that the bare roots are kept from drying out by ‘heeling in’ until you are ready to plant - simply dig a hole where the roots can be plunged into the ground and back-filled with the soil from the excavation to prevent drying winds or frost damaging the delicate root system. Containerised trees should be planted with the hessian root wrap left in place and with only the wires at the base of the stem loosened. Containerised and potted trees will need to be removed from their pots prior to planting.
7. When ready to plant your tree, excavate a planting pit large enough for the root system to fit comfortably with a minimum of 200mm clear space between the roots and the sides of the planting pit.
8. The tree should be planted to the same depth as it was originally grown at the supplying nursery. On bare rooted trees the soil line will normally be visible. With root-balled, potted or containerised trees, these should be planted so that the soil around the root system is level with the surrounding ground. These factors will determine the depth of the planting pit.
9. Take a little time during the preparation of the planting pit to separate the topsoil from the subsoil and any chalk. The latter should be disposed of entirely, while the sub-soil can be used to top up the pit following planting, if required. However, it is quality topsoil that should be placed around the tree’s roots. Improve the backfill material by adding well-rotted leaf mould or a bag of peat-free compost. If manure is available, this should be over one year old before being used, to prevent ‘burning’ the root system.
Not all gardens have room for large trees - some owners might wish to enjoy the shade, bird life, berries or other benefits provided by trees but, because of their experiences with problem trees, feel that by planting replacements in their small gardens previous problems may be continued as the tree matures.
Obviously, the smallest of gardens would not be the most suitable of places to attempt tree planting, although even these could, given sufficient light, support dwarf root stocked fruit trees either planted directly into the ground or in tubs. Also, true dwarf or very slow-growing conifers could also be considered.
The following selection would, with care of choice and siting, allow at least one tree or possibly more to be planted in an average town garden of around 10 x 7 metres.
A small tree with striated snake-like bark and bright green three-lobed leaves. The young growth is coral-red and in autumn the leaves turn to orange and red before falling.
Perhaps the most attractive of the ‘snakebarks’. A small tree with green and white striated bark and fine autumn colour.
One of the most beautiful of small trees, having foliage compiled of three separate leaflets often superbly coloured red and scarlet in autumn. The older bark on the main stem and branches flakes back to show cinnamon-coloured under-bark.
A popular maple, making a large shrub or small tree. Young leaves have a broad soft pink margin changing to white.
A distinct small and slow-growing Sycamore whose leaves in spring are a shrimp-pink, later changing to pale yellow-green and finally green.
A spectacular, very slow-growing form with young leaves of bright shrimp-pink changing to yellow green as the season progresses.
This Chestnut never reaches more than 3m in height. The flowers are white with red anthers while the leaves are bronzed when young and yellow in autumn before leaf-fall.
A lovely small tree whose leaves comprise five glossy green leaflets. The scarlet flowers are borne from June in 15cm panicles.
A small tree with deep brown shredding bark with flowers and fruits produced together in autumn. Unusually, this is an ericaceous plant (prefers acid soil) which tolerates our local alkaline soils extremely well.
A form of native Silver Birch, with silvery-white bark and diamond-shaped leaves ultimately making a dome or mushroom-headed small weeping tree. Yellow catkins are produced in spring.
Legend has it that this was the tree on which Judas hanged himself. That said, the tree is superb with a small low-forked canopy bearing rosy-lilac coloured flowers in spring before the leaves appear, and lilac seed pods in July.
The Thorns are among the hardiest and most adaptable of trees, surviving well even in industrial and coastal areas. Most are small trees with red, red-pink or white flowers and red berries.
There is a wide choice of species with the following being worthy of consideration:
A very free-flowering hybrid Laburnum with upright-growing branches clothed in long racemes of buttercup yellow flowers in June. The pea-like pods which follow contain poisonous seeds.
A small, flowering tree with long arching branches and crimson buds opening to white or pinkf-lushed flowers; the fruits are red or yellow.
A small tree producing blush-pink semi-double flowers from November to March. These last well as cut sprays for indoor decoration.
A small tree with long slender, almost perpendicularly, weeping branches.
A curious, very slow-growing Willow with twisted branches, pale green leaves and catkins in spring.
A small to sometimes medium native tree with a compact round head of branches. Leaves greyish white at first and later bright green above and white beneath and turning to gold and russet in autumn which contrasts with the deep crimson fruits.
A beautiful small tree of spreading habit with drooping clusters of fruit, rose-red at first, gradually changing to a pink-flushed white marble effect.
A commonly planted cultivar forming a dense compact column up to 5m; normally a broad, columnar bush with several main stems. A slow-growing tree, greyish green in colour, becoming bronzed in winter.
A small tree of slender columnar habit with upright sprays of dark green foliage.
As ‘Grayswood Feather’ but with golden yellow foliage.
A beautiful form of tall bushy habit, eventually making a small tree. The soft, feathery juvenile foliage is retained throughout life and becomes an attractive red bronze during autumn and winter.
A dense-growing, compact form of slender, columnar habit attaining 3m or occasionally 5m in height. Leaves are densely arranged. A very popular conifer, excellent for use in formal landscapes and gardens.
A slow-growing bush of ovoid or conical habit, eventually making a large shrub. The foliage is of old gold, shaded amber. Excellent against dark walls or green conifers.
Bats are colonial animals roosting naturally in trees and caves. With the reduction of their natural roosts many bats have adapted to the use of buildings where they experience new problems. The restoration of old buildings, combined with the use of chemical remedial treatments and the general intolerance of humans to their presence, continues to threaten the existence of many bats.
Some species of bats do rely exclusively on trees for roost sites, while others utilise trees for only part of each year. The availability of defects in trees, such as cavities and cracks, may have a significant influence on the number of species choosing such locations. However, all UK bat species feed on insects associated with trees. Oak, Ash, Beech and Scots Pine are particularly attractive to bats for roosting. Hedgerows and lines of trees are also used for navigation at night and the loss of such features can cause bats to abandon the current roosts.
The actual importance of trees to bat survival is variable and linked to species, foraging behaviour and even season. For Noctule, Barbastelle and Bechstein’s bats, the availability of a suitable range of roost sites in trees is crucial to their survival. Daubenton’s and Natterer’s bats are more reliant on trees in summer, while Long-eared and Pipistrelle bats have their major dependency in winter.
Bats use such sheltered places for much of their life activities - including giving birth to and raising their young - and such conditions are usually associated with mature or over-mature trees - another area of conflict. With health and safety legislation in place to protect people and property, tree management practices have tended to result in the felling of trees containing cavities or the removal of large fractured or dead limbs. However, with managed pruning, backed by regular safety inspections, it is now possible to delay the felling of trees in some locations and to prolong the usefulness of the defects for the benefit of the local bat population. In woodland the opportunities for such measures are greater, especially away from public areas and rides.
Sympathetic woodland management should include:
When re-planting is to be considered, include locally native tree species to encourage insect diversity and include rides, glades and open areas as sheltered feeding sites.
Bat presence should also be considered as part of woodland or arboricultural management surveys by considering the long-term management of any trees colonised by bats.
Where the need for pruning works is unavoidable, select the minimum operations necessary to meet requirements and assess if it is safe to compromise on felling to allow a tree to remain for roosting purposes.
Where practicable, make final cuts as far as possible above a defect that may support bats. If cracks are present these may be open due to the weight of limbs and might close if this weight is reduced by removal. Search large splits specifically for bat presence and if necessary use a wooden wedge to retain the crack in an open position.
Any ivy-clad trees felled should be left for 24 hours before removing limbs or ivy growth.
Bats may show little or no obvious signs of their presence and detailed examination of any tree prior to works being started is important to protect both the bats from harm and the person carrying out works from falling foul of the law.
All bats are currently protected under Schedule 5 of the Wildlife and Countryside Act and Schedule 2 of the Conservation Regulations 1994. The Act and Regulations include provisions that make it illegal to:
The legislation interprets a bat roost as ‘any structure or place which is used for shelter or protection’ and applies at all times whether bats are present or not. Any proposed works considered likely to destroy or disturb bats or their roosts must be advised to the appropriate Statutory Nature Conservation Organisation (SNCO) and a reasonable period allowed for their decision on whether works can proceed and what methods should be adopted, prior to works proceeding.
The United Kingdom is also party to The Agreement on the Conservation of Bats in Europe and is obliged to identify and protect from disturbance or damage all sites important to bats, including feeding areas.
In all cases where bats are found, please inform The Bat Conservation Trust or local bat group.
The Bat Conservation Trust
15 Cloisters House
8 Battersea Park Road
London
SW8 4BG
Statutory Nature Conservation Organisations
English Nature
Northminster House
Peterborough
PE1 1UA
Sheila Wright
Secretary
The Sussex Bat Group
5 Penlands Vale
Steyning
West Sussex
BN44 3PL
Ill-advised and badly executed tree work could lead to injury to people, damage to property and irrevocable damage to your tree. Tree work operations (arboriculture) require a high degree of technical competence, supported by training and experience. For these reasons such works should only be undertaken by well trained, competent arborists.
Unfortunately, anyone can call themselves a tree surgeon (arborist), place advertisements in Yellow Pages and locally available periodicals and offer a service. However, an advert alone does not guarantee quality of work, that it will be carried out safely or with the best long-term interests of your tree at heart. Competent arborists will have recognised and accepted certificates, especially the NPTC* certificate for chainsaw use which is compulsory. Such certification indicates that arborists have been trained and have been assessed as meeting a required standard of competency. Arborists may also hold other specific academic qualifications in arboriculture. Reputable tree care companies will use a range of general and personal safety equipment to protect you, your own and neighbouring properties, and themselves. Such companies will be pleased to furnish details of their insurance, qualifications and any professional membership, and will work to nationally recognised standards.
When you receive your written quotations, check that they include the following before deciding which one to accept:
While there will be many competent and qualified arborists who are not members of professional bodies, it may be helpful to note that the Arboricultural Association maintains a directory of quality assured arborists. The contractors contained in the directory are regularly assessed for health and safety procedures, office and business practices, as well as the quality of work.
Such contractors will display the AA Approved Contractor logo, and proof of current membership can be further checked through the AA website www.trees.org.uk/contractors.htm or by telephoning 01794 368717.
Individual arborists may be certified by the International Society of Arboriculture which assesses individuals for their knowledge and ability. Competent arborists will display the ISA Certified Arborist logo.
Hot summers and dry winters may give rise to subsidence-related damage to buildings. In some cases, trees are blamed for this damage.
Many householders have become concerned about trees close to their properties. In reality, tree root damage is less frequent and less inevitable than the publicity would suggest. Even when it is shown that trees may be contributing to damage, removal or severe tree surgery is often neither necessary nor desirable.
This information note describes how a tree may affect buildings and what may be done to reduce the problem.
There are many popular misconceptions surrounding trees and roots. These are the facts: there are two types of roots – woody and fibrous.
Woody roots radiate away from the trunk. They store food produced by leaves and anchor the tree. Their girth increases annually but not at the same rate as the trunk or the branches. These may give rise to direct damage to structures (see section on damage roots may cause).
Beyond the woody roots, fibrous roots extract water and mineral nutrients from the soil. They are hair-like (less than 0.5mm in diameter) in appearance and may only last for one year. These may give rise to indirect damage to property (see section on damage roots may cause).
Tree roots extend radically from the trunk. However, their direction and depth is hard to assess or predict. Foundations, roads, impervious surfaces and utility trenches can inhibit or influence their spread.
Roots require oxygen to live and are usually found close to the soil surface. Mature trees rarely have an anchoring “tap” root, or supportive roots, deep in the soil.
Roots can only grow through moist soil. They cannot search for distant sources of water or detect water inside a sound pipe. When a root reaches an area of dry soil it will stop growing in that direction.
Trees need water to grow. Leaves produce the energy for this growth using water largely supplied by the roots. Over time, as a tree produces more leaves, its potential to take up water from the soil is increased. If the number of leaves is reduced, i.e. by tree surgery, the amount of water taken up by that tree is also reduced.
Tree height bears no special relation to its potential to extract water from the soil: this is related to the type of tree, number of leaves and their surface area.
Direct damage may be caused by the physical expansion of woody roots as they grow. This can affect light structures with shallow foundations, e.g. porches, boundary walls, patios, driveways or pavements. The solution is usually to modify the affected structure, allowing for any future expansion of the root.
Root pruning should be avoided wherever possible as this may introduce disease, ‘rob’ the tree of vital food reserves, or make the tree unstable.
Roots may also grow into and block cracked and leaking drains or sewers. Before roots can enter such services, they must be leaking water. If by chance a root encounters the wet soil caused by a leak, increased root growth can occur and may result in entry and blockage of the service. The remedy is to make the service watertight.
Indirect damage may result from the extraction of soil moisture by fibrous roots of trees and other vegetation. This only occurs on certain soil types which are shrinkable, usually clays. The volume of these soils is dependent on their ability to retain the moisture contained within them: a reduction in soil moisture, caused for example by fibrous tree roots, leads to soil shrinkage. If this occurs beneath foundations, movement and damage may occur.
Irrespective of tree root action, shrinkable soils contract and expand during the course of a year as a result of seasonal weather conditions and water abstraction from something as simple as grass. This natural ground movement alone can result in damage to structures.
Movement of built structures resulting from soil shrinkage is termed subsidence. Roots removing soil moisture beneath buildings may cause damage.
However, structural damage can occur for a variety of reasons, including shallow foundations in shrinkable soil; normal seasonal soil movements; inadequate foundations for structures which are tied to the main building (e.g. bay windows, garages and conservatories); overloading of central walls; lack of flank wall restraint; land slip; drainage defects; and vibrations caused by constant passage of vehicles.
Thus the effects of trees are rarely the sole cause of subsidence.
There are thousands of trees in Brighton and Hove, the vast majority of which co-exist happily with buildings.
The presence of a tree near a building does not mean that subsidence is inevitable.
Even if it is established that a tree is affecting a property, removal is not usually necessary. Tree surgery (i.e. reduction in the number of leaves) will reduce the tree’s potential to extract soil moisture and allow some soil re-hydration to occur. The soil will then increase in volume leading to some closure of structural cracks. Subsequent tree surgery frequently achieves ‘stability’ of the foundations, offsetting the need for costly work to the building.
Movement resulting from soil expansion is termed heave.
This is the opposite of subsidence. It is the result of an increase in soil moisture levels causing an increase in volume. Heave can occur as a result of leaking drains, overflow pipes or the removal of a tree growing close to a property.
Heave is potentially more destructive than subsidence. Therefore advice should always be sought before such trees are removed.
The benefits of applying mulch to our shrub beds and borders are well-known to most gardeners and landscape managers. Long dry summers are becoming more frequent and expensive shrubs and plants are being lost as hosepipe bans increase. An application of mulch will not only enhance the appearance of the beds, but will retain all important soil moisture. Brighton & Hove City Council has a programme of recycling all waste prunings by processing them through woodchippers. These are the large noisy machines ‘eating’ the branches that you see the tree surgeons use. These chips are taken back to our yard, composted for a year and then used on shrub borders throughout the City. “So, what are the benefits of using woodchip mulch on my garden?” you may ask. The list is a long one but the highlights are as follows:
Wood chip mulch is unsuitable for digging into the soil as an improver until it has been composted or has had additional nitrogen added to it. Composting should take from six months to a year with the pile being turned regularly. The application of mulch to the borders should be at least 100mm deep but may need topping up from time to time as earthworms draw down the compost into the soil.
Woodchip mulch may be purchased direct from your local garden centre or possibly from local arboricultural contractors. Woodchip from the garden centre is likely to have been composted for the required period and can be used immediately. While this may also be the case when buying from your local arboricultural contractor, it would be wise to check on the age of the material available before purchase.
You may find that toadstools appear on the chips during autumn giving concern that this may be harmful to the plants in the border. Fortunately, the fungi are not harmful and only feed from the chips themselves. They are not harmful to children, but they should be made aware that nibbling of toadstools and mushrooms is dangerous and should be discouraged.
Trees are often planted as features within gardens or as screens on boundaries. If they are not regularly maintained, they may outgrow their position causing common problems such as reducing light levels to properties and gardens, becoming obstructions, and causing problems by overhanging neighbouring boundaries.
Once the decision has been made to prune, your next decision is whether or not to tackle the job yourself. In the case of a large tree where you need to remove big branches in the upper area of the crown, it may be best to seek professional advice (see Arboricultural Information Note No. 4).
As a general rule, pruning is best carried out when the tree is dormant, between November and February. There are, however, exceptions to this rule. All Juglans species (Walnut) will ‘bleed’ (prolific leaking of sap) profusely if not pruned in full leaf in mid to late summer. Many Rosaceae species such as Cherry, Apple and Plum, are best pruned in the summer months as they are susceptible to the fungal disease “Silver leaf” (Chondrostereum purpureum). This fungus prefers the damper conditions of autumn/winter and is less likely to be active during the drier summer months.
Many broad-leaved tree species, such as Birch, Maple and Hornbeam, also have a tendency to ‘bleed’ if pruned between late winter and early spring. This condition is caused by increased sap flow in preparation of bud development. Therefore it is best to avoid pruning at this time if possible. It is, however, unusual for this condition to cause long-term damage.
Any pruning carried out on an actively growing tree will bring about a response. Leaves obviously provide a vital function for the tree, producing both sugars and starches through the process of photosynthesis and allowing the transfer of gases via transpiration. The tree’s natural response to a reduction in leaf cover is to produce vigorous re-growth in an attempt to compensate for this loss. This can often take the form of dormant buds within the crown and on the stem becoming active. In time these can create a denser crown than before pruning took place.
When a branch is removed from a tree, its natural response is to compartmentalise (isolate) the area in a bid to resist any inward progression of fungus and other diseases and to protect new wood formed after pruning has taken place. Incorrectly placed pruning cuts can seriously inhibit this process and have long term detrimental effects on both the tree’s health and stability.
The position of the cut should be selected with care; as already mentioned, it is important to remove a branch at the correct point. At the junction where a branch joins a stem there is normally an obvious ridge of tissue (not always obvious in conifers); this is known as the branch bark ridge/collar (fig 1). It is important to cut as close to this as possible, but NOT into it. This area is responsible for the healthy sealing of the wound. Care should be taken to prune back to a healthy bud or branch junction. Failure to do this may result in leaving a stump, which may then die back to the nearest bud/junction and facilitate the advancement of pathogens (disease organisms).
When removing heavy branches, care should be taken to avoid tearing. It is advisable to use the 3-cut method (Fig 2). This involves: (1) making a cut on the underside of the branch to be removed several centimetres away from the final cut – this helps to avoid the branch tearing; (2) making a further cut on the upper side of the branch several centimetres in front of cut 1; (3) the small remaining stub can then be pruned back to the aforementioned branch bark ridge. It should be remembered that the removal of large heavy branches could be a hazardous procedure and professional advice is strongly recommended.
Many trees, as they develop, accumulate dead twigs or branches. This is often a result of light deprivation as the crown develops and matures above. These should be removed (Fig 3) as they can be unsightly and can harbour pests and diseases.
Wound dressings were once thought to accelerate wound closure, protect against insects and diseases, and reduce decay. However, research has shown that dressings do not reduce decay and rarely prevent insect or disease infestations. It has also been established that the rapid closure of wounds has the potential to create future structural weaknesses. A situation where a wound treatment would be recommended would be as a precautionary measure against conditions such as Silver Leaf.
The following list is intended to give an idea of the range of tools suitable for the tasks mentioned above.
These are hand-held pruners with one or two cutting blades made of stainless or carbon steel. There are 3 types: Anvil secateurs which have a straight upper blade which cuts down on an anvil block (this type is best avoided as the cutting action can cause a crushing type injury); by-pass secateurs which work like scissors – the upper sharpened blade cuts against a broad lower blade; parrot-beak secateurs, which have two sharpened blades which cut when closed together. Secateurs are used for light pruning – they cut through material up to 10mm in diameter.
There are several different types: double-edged pruning saw, folding saw, Grecian saw, and bow saw; all are steel and have heat treated teeth. All have teeth designed to cut on the pull stroke. They are used where required cuts will be above 25mm in diameter. The choice of saw type depends on the size of branches to be cut and the amount of working space within the shrub or tree branches. It is recommended that woodworking saws are not used to carry out pruning.
These have one or two cutting blades. They work in the same way as secateurs but have handles up to 60cm long. There are three types: anvil loppers, which have a straight upper blade which cuts down on an anvil block (this type is best avoided as the cutting action can cause a crushing type injury); by-pass loppers, which work like scissors – the upper sharpened blade cuts against a broad lower blade; parrot beak loppers, which have two sharpened blades which cut when closed together. Loppers are a useful tool for working high up, or in dense, prickly shrubbery. The long handles offer more leverage and cut stems up to 25mm thick.
These have a cutting device on the end of a long pole. The hook is placed over the branch and cut by operating the handle. The wire or cord pull from the handle activates the spring-loaded carbon steel blade. Tree pruners may also have a saw attachment. They are used on light branches up to 25mm diameter that are out of reach.
Blades need to be kept sharp, clean and dry, moving parts need oiling and blades need regular replacement. Strong gloves, eye and head protection should be worn.
Before carrying out pruning work on your tree it is advisable to consult the City’s Arboricultural Service to ascertain whether your tree is growing within a conservation area or is under the protection of a tree preservation order.
Enquiries can be made by calling 01273 292929.
Similarly, general enquiries concerning any elements of this information note can be made by calling the Arboricultural Officers on 01273 292929.
While this scale insect is commonly named after its known presence on Chestnut, it is equally at home colonising Lime, Sycamore and Maples, Magnolia, Bay and other ornamental trees.
First noticed in London Boroughs in the 1960s, this insect has migrated swiftly in the south of England where it is now common and is known to be prolific as far as Yorkshire and Lancashire. The Scale thrives on trees in situations enjoying warm microclimates such as those growing in roadside pavements on major vehicular routes, paved squares, car parks, parks, and naturalised woodland.
The Horse Chestnut Scale is often mistaken for a fungal infection, but each dark brown shields-haped structure, surrounded by a white waxy wool-like mass some 4mm across, serves as a shelter for fully developed scales (adult insects), immature scales, known as nymphs, and a clutch of white eggs. These structures are most noticeable in early summer, deposited on the bark of the main trunk and often extending into the branches of the lower canopy. Each of the dark, shield-shaped outer covers are constructed of Chitin (a hard, horny constituent of the bodies of some insects) and are actually the dead bodies of the egg laying females.
The eggs hatch in late June or July with the newly emerged nymphs moving onto the foliage where they begin to suck sap from the undersides of the leaves. Prior to the autumn leaf fall, the still immature scale insects move to the branches and trunk where they over-winter. Development to adult scales is completed during spring and these commence egg laying on the bark in late April into May. The adult scales are parthenogenic, a characteristic common in many lower forms of insects, providing the ability to reproduce without fertilisation being necessary.
Infestations of the Horse Chestnut Scale, while unsightly and possibly visually alarming, have little or no detrimental effect on the health or vigour of the colonised trees, therefore control is not necessary. However, on young, easily accessed trees it is feasible to scrape the mature scales and egg mass from the trunk and branches using a stiff brush. These should be targeted in April and May and such action will stop the next generation from developing.
The spraying of chemicals to control the problem on larger trees is not recommended as the range of chemicals available to effect control is limited and non-selective, and the equipment necessary to introduce these are specialist in nature. As the problem is purely visual, chemical treatment is not recommended under any circumstances.
Fireblight is a disease caused by the bacterium Erwinia amylovora. Originating in the United States it was first recorded on Pear trees in Kent during 1957 and then spread slowly to affect trees in most parts of England and Wales before progressing northwards.
The disease affects Rosaceous trees and shrubs with apple-like fruits, principally Apple, Pear, Thorns, Whitebeam, Rowan, Fire Thorn and Photinia species. Cherries, Plums, and Swedish Whitebeam are not affected. Symptoms are varied and diverse and include wilting followed by browning of the leaves (resembling scorching), fruit and leaves persisting on the tree, shoot dieback, bark cankers and red-brown staining in the inner bark. Symptoms are most obvious between June and September or after leaf-fall.
In ornamental plants the severity of damage or death is dependent on particular species and weather conditions. Wet and warm conditions aid the production of infectious Slime Flux (a mucilage containing myriads of bacteria). Warm sunny days encourage increased activity in flying insects, especially bees, which assist in the spread from plant to plant situated within a few hundred metres of a diseased plant. Summer storms, often associated with heavy rainfall, may cause damage to leaves and may provide additional entry points for the bacteria. The infection can also be spread on pruning tools.
Once inside the tree, the bacteria multiply and spread rapidly through the intercellular spaces within the inner bark, killing it. Less susceptible plants may suffer no more than isolated shoot or twig death, although susceptible species are not likely to survive.
The risk of infection can be reduced by:
Winter moth is aptly named: the adults emerge from November to mid-January. It is one of several moths that are active during the autumn to spring period.
In many of these ‘cold weather’ moths, the two sexes are quite different. Males have fully developed wings (above) and a typical moth-like appearance, but the females (left) are either wingless or have greatly reduced wings, making them incapable of flight.
Winter moths emerge on mild evenings from pupae in the soil. While the drab, greyish-brown males can fly about, the females have to crawl up the trunks and along the branches of trees until they reach the twiggy shoots where they mate and lay their eggs. These eggs hatch in spring when the trees come into leaf. Many deciduous trees and shrubs, including oak, hornbeam, lime, sycamore, mountain ash, birch, rose, apple, plum, pear and cherry are host plants. The caterpillars are up to 20mm long and pale green with stripes along their bodies.
Winter moth caterpillars can be so abundant on oak trees that, in combination with other moth caterpillars, they cause severe defoliation in spring. The trees survive, producing new leaves in early summer as caterpillars are fully fed by late May or early June, when they move down into the soil to pupate.
Winter moths can damage garden trees, especially fruit trees. Fruit growers can protect these by placing sticky grease bands on the trunks in late October. This forms a barrier against the crawling females and reduces the number of eggs laid on the twigs. Grease bands offer no protection against moths with winged females such as codling moth. However, it is these that cause small maggots in apples.
Caterpillars of winter moths and other moths are taken in huge quantities by tits and other birds when they are rearing chicks. Male winter moths usually rest on tree trunks and other vertical surfaces with their heads uppermost. If you see one with its head down, look more closely; it is probably in the act of mating, the tip of its abdomen linked to that of a wingless female.
Peach Leaf Curl is caused by a fungus (Taphrina deformans) and is a disease affecting peaches, nectarines, flowering almonds, apricots and ornamental Prunus. In spring young leaves develop red and pale green blisters. Later they become curled and swollen with a powdery coating of spores, eventually turning brown, then withering and falling.
Severe attacks weaken trees and may lead to poor cropping and die-back. Spores overwinter in cracks in the bark, on shoots and bud scales (but not on fallen leaves). Attacks are most severe in cold, wet weather. Feed and water affected trees regularly.
Leaf curl can be prevented by spraying trees with copper sulphate (Bordeaux mixture) or mancozeb (Dithane) as soon as buds begin to swell (late January) to prevent spores entering developing buds. Spray again in autumn to minimise risk of infection the next season.
A polythene or glass covering for plants grown against a wall or fence can reduce symptom severity; leave in place from January to mid-May.
More resistant Peach (Prunus persica) cultivars include ‘Avalon Price’, ‘Red Haven’, ‘Dixi Red’, ‘Hylands’, ‘Robin Redbreast’, ‘Redwing’ and ‘Rochester’.
Although numerous spores are produced by the fungus in spring, there is little spread of the disease from affected leaves to healthy ones, so the second flush of leaves usually remains healthy. The fungus dies out on fallen leaves once spores have been released; removing fallen leaves before the bloom of spores appears to minimise the risk of infection the following year.
Cold winter weather can be surprisingly damaging, even to hardy plants, but warm spring days then cool nights can also damage leaves and flowers. The resulting symptoms can be confused with pest or disease damage.
Plants react differently to cold, and to different degrees of cold. Frost causes damage to tender plants when ice crystals form from the watery cell contents, breaking cell walls and damaging cell proteins, causing tissue browning and softening. Hardier plants may show leaf scorch, browning, drying and papery thinning of tips and margins.
Bedding plants and tender vegetables such as potatoes and tomatoes exhibit a range of symptoms. Leaves may darken, yellow, curl, scorch or die completely. Cold stress can be hard to distinguish from drought, over-watering, nutrient deficiencies or disease; the prevailing weather may be the best clue.
Track temperature changes with a glasshouse maximum-minimum thermometer and keep horticultural fleece handy to protect plants in cold weather. Harden off tender plants thoroughly to reduce spring cold stress.
Cold, wet soils, cold winds and low night-time temperatures can cause reddish-purple leaf discolouration. Photinia is particularly prone to this reaction, forming leaf spots that look like a disease. Rhododendron and Viburnum rhytidophyllum often suffer temporary leaf curling and drooping in cold weather. On exposed sites, temporary windbreaks or permanent shelter belts can help protect plantings.
Most non-tender plants recover from cold damage, producing new foliage as the weather warms.
The Grey Squirrel is found throughout England, Wales and some areas of Scotland. It was introduced from North America on several occasions during the period 1876 to 1930 and in many of these areas has displaced the native Red Squirrel. The diet of the Grey Squirrel is extremely varied consisting of the buds, nuts, bark, berries, seeds, and fruit of many species of shrubs and trees.
Squirrels are known to collect large seeds and nuts and store these by burying them in the ground, relying on scent alone to retrieve these at a later time. A number of these are never found again and in this way they aid the spread of seed from the parent plant, ensuring the spread of new trees.
Grey Squirrels also cause damage to established trees by gnawing at the bark of usually thin-barked trees to get to the sweet layers beneath (Phloem Tissue). This tissue is responsible for moving sugars around the plant’s system. If this feeding damage is so extensive and extends completely around a branch or stem, the flow of sugars will be halted and the stem or branch will eventually die. However, the removal of even some bark and associated tissue can restrict the growth of a tree and allow the entry of secondary infections through the wound that may affect the tree’s health or stability.
Bark stripping occurs between April and early August to trees in the 10 to 40 years of age bracket with thin-barked deciduous trees such as Sycamore, Beech, and Oak, and coniferous species such as Pine, Spruce, and Larch being attacked regularly.
Some damaged trees will ultimately die and some will succumb to secondary fungal infections. Both may present problems to tree owners by making the tree or specific branches unsafe, requiring expensive tree surgery to resolve issues. In commercial plantations the loss of trees may have an immediate financial impact, while trees that are damaged may also become unsalable at some stage due to staining or other imperfections resulting from fungal or other pathogenic activity.
Tar spot is an unmistakable and conspicuous fungus of little importance as a tree disease. The principal hosts of this fungus are Sycamores and Maples (Acer species).
The fungus overwinters on fallen leaves with fresh spores being produced during the following spring. The spores, when released, have a sticky coating and attach themselves to newly forming leaves, causing striking and visually obvious raised shiny spots on the infected leaves.
Early in the year these fruiting bodies may appear as yellowish spots, later turning black and remaining until autumn’s leaf fall, the characteristic black reflecting the popular common name.
Leaves often support several Tar Spots, each generally around 1.5cm in diameter. On close inspection, these appear ridged while on the reverse side of the leaves the corresponding section of each leaf directly below the Tar Spot is cupped.
Fortunately, while somewhat unsightly, the fungus does not cause any lasting or serious harm to established trees, although its presence may be associated with some early leaf fall.
The disease is rare in towns and cities, a fact often attributed to the fungicidal action of air pollutants, especially sulphur dioxide. However, there is evidence that this may in fact be more attributable to the fact that streets are swept of leaves throughout the winter period and this action deprives the fungus of vital host material on which to overwinter, thus breaking the life cycle.