Plant Pest and Disease Management

Every day we leave our homes and rarely take the time to appreciate the incredible landscape we have all around us. Our gardens, parks, public open spaces, countryside and woodlands all contribute to our patchwork landscape which provides us with so many benefits including visual amenity, screening, health, wildlife habitat and recreation.

Due to our climate in the UK we are able to grow literally thousands of species of plants from right across the world, adding visual and genetic diversity. Our global economy means that the plants in your local garden centre or nursery may have originated in Europe, Africa or Asia and have been transported hundreds if not thousands of miles. These exotic plants can be expensive but give parks and gardens individual character.

Scale insects pierce bark and suck sap. Photo courtesy of Donald Holbern

Scale insects pierce bark and suck sap. Photo courtesy of Donald Holbern

Unfortunately the plants, soils, packaging and containers may also contain pests and diseases which could, if they become established, wreak devastation on our landscape. This is where responsible plant pest and disease management comes in.

It’s not only imported pests and diseases that can cause a problem to our gardens and wider landscape but also those which are naturally present. Unacceptable damage can be caused when they reach epidemic levels due to favourable conditions or the loss of natural predators.

Although pests cause damage to our plants they also contribute to the wider ecology and bio diversity providing a food source for desirable species of mammals, birds and insects. Unless they are recently introduced species eradication is rarely possible or desirable. Some although unsightly cause little actual harm particularly if the plant has good vitality.

Plant Pest Management

Aphids tend to attack new shoots

Aphids tend to attack new shoots

Pest management should start at the planning stage. Planting the right plant in the right place is a vital mantra. By selecting plants which are suitable to the specific site conditions in terms soil type, acidity and alkalinity (Ph), exposure, orientation, available light and surrounding features they will maintain good vitality (health) and be more able to resist colonisation and attack. Plants which are not suitable will have continued poor vitality throughout their lives making them susceptible to pest and diseases. Arboriculturalists at Tree Maintenance Ltd. can carry out site assessments to determine the growing conditions and assist our clients in in specifying plants which are suitable for their individual environments.

Although reputable nurseries will not sell poor quality or infected stock, ideally plants should be checked at the point of sale for vitality, pests and diseases. This check should include the leaf and buds, twigs, branches, trunks, root collar, and roots. Where plants are grown in containers the compost should be checked together with the roots exposed when lifted from their containers. Plants showing poor vitality or damage by pests should be rejected. Plants should be rechecked on delivery along with any packaging which can contain pests itself to prevent new pests being bought to site.

Correct handling and planting will ensure that plants are maintained in optimum health. They should be carefully handled and installed at the earliest opportunity in order to maintain their vitality. If plants are to be stored for a short period they should be protected from drying and damage and watered when required prior to installation. Tree Maintenance Ltd. Arboriculturalists are experts in plant supply, handling and installation and can provide support to our clients as part of landscaping projects.

Once the plants are installed and established good regular observation is the key to managing pests and diseases. Knowing what the healthy plant looks like is an important start. The majority of pests are notoriously difficult to find as they may be nocturnal, feed on the underside of leaves or live in/on the soil, roots or shoots of plants. Most often, it is the type and location of damage and symptoms of decline in plants leads to identifying the actual problem which can then be confirmed by finding other indicators or laboratory analysis.

The Horse Chestnut Leaf Minor consumes the leaf cells from within

The Horse Chestnut Leaf Minor consumes the leaf cells from within

Damage from insect pests can be varied and wide-ranging and include holes, notches, galls, leaf mining and distortions. Buds my fail to develop, be eaten or mined by insects. Insects such as Red Spider Mites consume the leaf surface whilst larvae of other species consume the cells from within e.g. Horse Chestnut Leaf Minor. Twigs may be mined by larvae resulting in twig or branch failure or have exit holes which indicated underlying damage. Shoots become colonised by Aphids or scale insects which pierce the bark and suck sap.

Trunks and larger branches can be colonised by sap sucking scale insects which either cause direct damage or provide entry points for secondary diseases. Other insects mine the living cambium beneath the bark which interferes with the vascular system of the plant resulting in leaf and crown symptoms together with areas of dead or missing bark.

Roots and Root Collar – should be checked as far as possible for those signs listed above but also to check to see if the soil is saturated or if the soil smells different.

Ganoderma fungal fruiting bodies on Beech

Ganoderma fungal fruiting bodies on Beech

Fungi and bacteria can cause decay and dysfunction in all parts of a plant including the roots trunks, twigs and branches. Fungal decay can be tolerated in trees up to a point but advanced decay can result in in partial or complete failure.

Fungal fruiting bodies can range from tiny inconspicuous fungal dots which only last a few weeks to toadstools and mushrooms which last a few weeks to large perennial brackets which last for years or even decades.

Some fungi such as Honey Fungus can travel through the soil from nearby infected plants to colonise new hosts. Checking nearby plants and considering site history is an important part of the diagnosis process.

Dead Norway Maple following colonisation by Honey Fungus

Dead Norway Maple following colonisation by Honey Fungus

Where a new exotic pest or disease is discovered, there may be a legal duty to notify government agencies such as Forestry Commission or The Food & Environment Research Agency (Ferea) Plant Health and Seeds Inspectorate. These organisations have powers to investigate outbreaks, restrict imports and movement of plants and plant produce, or specifying treatments or inspections which have to be carried out to ensure control or eradication of pests before they become established.

Plant Pest Control Measures

Pests can be controlled using various methods either in isolation or tandem with one and other. Maintaining and improving the vitality of the plant should always be considered as a first step as this makes the plant more disease and insect resistant.

Good site husbandry and the careful disposal of infected material can limit the spread and establishments of pest and diseases. Biological control, where available, is often better than using chemicals and can maintain pest numbers at an acceptable level. These can include- nematodes, insects, birds, bacteria and viruses which kill their hosts or limit their capacity to injure plants.

Chemical treatments offer a cost effective control method of many insect, fungal and bacterial disease. Professional operators must be certificated to apply chemicals. Chemicals may be in the form of mists, washes powders or tablets. Some can be injected straight into the vascular tissues and are carried throughout the plant to provide long term protection. Care needs to be exercised to ensure that none target species are unaffected.

Traps and mechanical control can also be effective. Hand picking can reduce numbers locally. The use of traps either mechanical or pheromone requires careful monitoring and supervision. Shooting is an option and can be effective against deer, grey squirrel and rabbits. The use of high pressure jets can be effective when controlling insects or caterpillars high in the tree canopy although this normally requires a specialist contractor.

Our highly experienced and qualified arboriculturalists at Tree Maintenance Ltd. provide an identification and diagnosis service of plant pests, diseases and disorders. We are able to assess their implications and advise on their future management to protect our landscape in a sustainable and cost effective way.

Do you have concerns about any of your trees? Contact Tree Maintenance Ltd. on 01285 760 466 or via the contact form and arrange for one of our experienced tree consultants to help you choose the best course of action.

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Steve Cullis

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