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Trees and Shrubs : Pests and Diseases

Pests | Diseases

Pests 

A group of caterpillars on beech

A group of caterpillars on beech

Rabbits and hares cause very serious damage in rural areas. Fencing is the complete answer. Wrapping the stems of young trees with heavy polythene is effective too.

Greenflies feed off many trees and shrubs, especially honeysuckle, viburnum, privet, beech, lime, flowering cherry. Control is usually not necessary.

Caterpillars of many kinds eat the leaves of trees and shrubs, usually leaving holes. Damage is slight and control not necessary.

Leaf miners attack many trees, notably holly, leaving twisting tracks and blisters on the leaves. Though unsightly, control is not necessary.

Red spider mite attacks many trees and shrubs. Control is not necessary, except on dwarf spruces, which could lose all their leaves. Spray in April or May.

More detail on these in the section on Gardening techniques: Pests 

Diseases

Honey fungus, or bootlace fungus (Armillaria) is a widespread and serious root disease. Privet, griselinia, cypress, lilac, birch, willow and pine are very susceptible. The fungus grows in the roots just below the bark, producing white fluffy growth, black bootlace-like strings and yellow mushrooms.

Pine trees killed by waterlogging

Pine trees killed by waterlogging

Butt rot is a similar root disease of conifers, common near old shelter belts and forest plantations. There is no control. Remove stumps.

Phytophthora root rot has become a common disease since the advent of container-grown plants. Lawson’s cypress, rhododendron, heather, flowering cherry, yew, beech and lime are susceptible. The affected plants wilt and die slowly over a period of time, especially in summer. Avoid nurseries where there are dead and dying Lawson’s cypress.

Heart rots are diseases of the heart wood of large trees. Fungi enter the trunks through broken branches, and rot the heartwood. Brackets appear on the tree and release spores. Oak, beech, chestnut, ash, walnut and birch are often attacked and seriously weakened.

Silverleaf is a disease mainly of flowering cherry. The leaves on one or two branches go silvery and the tree eventually dies. Bacterial canker is another serious disease of the plum and cherry family, including laurel. Gum usually exudes from a main branch, and little holes (shot-hole) may appear in the leaves. The tree usually dies.

Die-back is a general name for the damage caused by a variety of fungi on small twigs and branches of many different trees and shrubs. Cut out dead shoots. Dutch elm disease is a very specific disease of elm that starts by killing a few small branches, and eventually the tree itself.

Leafspots and powdery mildew, caused by a variety of fungi, attack a wide range of trees and shrubs. These are usually harmless, if a plant is weakened, give it some fertiliser to speed recovery.

Fireblight affects apples, pears, cotoneaster, pyracantha, hawthorn, mountain-ash and Japanese quince. It first kills a few branches, these retaining their leaves as though scorched by fire. If suspected, notify the Dept. of Agriculture.

More detail on these in the section on Gardening techniques: Diseases

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