Controlling diseases on large trees and shrubs sometimes requires drastic measures. However, many species can support pest colonies without detriment.
- Symptoms: This bacterial disease enters the shrub through a wound and produces whitish swellings (galls), on top of the roots or at the base of the trunk. These turn black and blocks sap circulation, leading to death.
- Shrubs and trees affected: Cypress, euonymus (spindle). Ribes sanguineum, rhododendron, and roses.
- Treatment: There is no effective remedy for crown gall. As soon as the symptoms are recognised, dig up and burn affected plants. Replant new stock in another place. Prevent the disease by improving soil drainage around the plant and feeding with a high phosphate and potash fertiliser. Avoid root damage when transplanting.
FOMES ROOT AND BUTT ROT
- Symptoms: Dark red-brown fungus grows on the trunk, or butt, of the tree at ground level. The lower surface is covered in minute pores. Fine white filaments appear under the bark, penetrating to the centre of the trunk. The needles on conifers turn yellow and the tree gradually dies.
- Trees affected: Spruce, pine, elder, birch, oak, beech, larch.
- Treatment: Dig up and burn the affected tree. Replace the soil before replanting.
- Symptoms: The foliage discolours, wilts and will progressively die back. The whole plant can die rapidly or hang on for years. Infected plants produce a white fungal-smelling growth beneath the bark at the base of the trunk. Black root-like 'bootlaces' grow on the outside of roots, which is how the fungus spreads to other plants. Clumps of honey coloured toadstools may also grow around infected plants.
- Shrubs and trees affected: Most woody plants, climbers and some bulbs. Box, buddleja, caryopteris, chestnut, fir, holly ,and monkey puzzle.
Treatment: There is no fungicide to control this disease. Dig out and destroy infected plants immediately, removing as much root and infected soil as possible. Replant with disease-resistant annuals or perennials.
Trunks and branches
- Symptoms: Infected branches shrivel. Cankers appear at the base of shoots and on the leaves along the veins, making the leaves appear burnt.
- Shrubs And trees affected: Many shrubs and trees, such as cornus, plane, Salix, walnut.
- Treatment: Pick up all infected leaves, prune out seriously damaged branches and burn it all. Spray the whole plant with a copper-based fungicide and repeat according to manufacturer's instruct ions if the disease continues to affect the tree.
- Symptoms: The bark flakes off to reveal galleries that radiate from a central point where eggs were laid.
- Trees affected: Most species, especially elm.
- Treatment: Since the bark protects the larvae, treatment is ineffectual. Cut off affected branches or cut down and burn infected trees. As a preventive measure, ensure that your trees are healthy, and therefore less vulnerable.
- Symptoms: Fungi develop in clumps on the trunk and branches. The tree weakens and its branches become brittle.
- Trees affected: Ash, beech, larch, oak, pine, plane, Robinia pseudoacacia, yew.
- Treatment: Scrape off minor infestations with a knife. When established, the fungi will have penetrated the tissue, and felling is the only option.
- Symptoms: Swollen-edged cracks form on the bark. The bark tissue is exposed and oozes a whitish substance, or resin in the case of conifers. The tree then withers and dies.
- Shrubs and trees affected: Ash, beech, chestnut, conifers, hawthorn, laurel, lime, plane, poplar, rose, sorbus , willow.
- Treatment: Cut the diseased tissue back to healthy wood with a pruning knife, then burn the parings.