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Garden Plant Disorders.

Pests and diseases of shrubs and trees.

     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.
  • 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.
Bark Beetle
  • 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 pseudoacaciayew.
  • Treatment: Scrape off minor infestations  with a knife. When established,  the fungi will have penetrated the tissue,  and felling is the only option.
Bracket Fungi
  • 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.

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