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Page 2

Garden Plant Disorders.

Pests and diseases of shrubs and trees.

You can expect some type of insect pest to attack your garden plants. That is nature, but not every insect in your garden is does harm to your plants. To control insects in your garden, you need to know what kind of insect you are dealing with. The first line of defence against insect pests in the garden; is identification.
  • Symptoms:  Branches are covered with little orange-red pustules that rapidly multiply eventually killing the plant.
  • Shrubs and trees affected: Most ornamental species.
  • Treatment:  Prune out the affected growth to healthy wood, burn the pruning’s and sterilise tools after use. Clean up infected dead material around the garden, as this can be a source of infection.
  • Symptoms:  The affected stem thickens, enlarges and flattens, forming an undulating ribbon, sometimes with curling edges.  The plant continues to grow and flower as normal.
This is an accident of growth and not a disease.
  • Shrubs affected:   Daphne, forsythia.
  • Treatment:  There is no remedy.  If too unsightly, simply cut off the affected shoot.
  • Symptoms:  Entries to galleries that leak sap can be seen close to the soil. Infected mature trees gradually wither; younger trees become brittle from ground level upwards.
  • Trees affected:   Birch, ash, poplar, willow.
Treatment:  Seriously infested trees should be felled. Keep down grass around the trunks as it makes a good place for the moth to lay eggs.
  • Symptoms:   Sawdust at the base of trees beneath galleries bored out of the trunk.
  • Trees affected:   Poplar, Willow
  • Treatment:  Destroy the larvae by scraping the galleries with a steel wire.  If infestation is too far advanced, fell and burn the tree.
  • Symptoms:   Conifer needles turn yellow and then brown.
Fungi gradually invade the whole branch and affected parts are black-spotted.
  • Trees affected:   Conifers.
  • Treatment:  Pick up and burn infected needles. Use a foliar feed throughout the summer to aid recovery.
  • Symptoms:   A blackish flux appears at the base of the trunk.  The leaves turn yellow, then brown, and the shoot tips, wither.  Finally the shrub dies.
  • Shrubs  and trees affected: Aucuba,  catalpa, cornus, holly, elm, skimmia,  rhododendron.
  • Treatment:   There is no cure. Remove and destroy the plant and infected soil. Improve the drainage and avoid damage to roots when transplanting.
  • Symptoms:   Small clusters of dense and stunted shoots appear at the tips of branches, causing the foliage to yellow.  If shaken, a white dust drops off.
  • Trees affected:   Birch, carpinus.
  • Treatment:   This disease is more unsightly than dangerous.
Cut off 'brooms' and burn the branches to prevent spores spreading.


Symptoms: Dark brown spots appear on the foliage. The spots grow larger and finally join together. At the same time. The leaves turn yellow fall off leaving the stems entirely bare.
Shrub affected: Rose.
Treatment: Collect up infected leaves, prune out heavily diseased wood and burn. In the spring, spray the whole rose plant and the surrounding soil with an approved fungicide and repeat as directed.

  • This disease attacks flowers as well as leaves and fruits. It affects mostly weak, damaged shrubs.
  • Symptoms:  Grey caterpillars with red marks form colonies in woven silky nests that hang in trees and hedges.
  • Shrubs and trees affected: Many types of trees and shrubs including apple, cherry, hawthorn, lime, plane.
  • Treatment:   Prune our the overwintering nests of caterpillars (wear gloves and take great care to prevent contact with caterpillar hairs, which are highly irritant).
When  the caterpillars are active in spring, spray with Bacillus thuringiensis or an approved insecticide.
 Prevention of  black spot is extremely difficult with many strains of the fungi being resistant. However, regular raking around the plant with a hoe and pruning and burning of infected material will certainly help.
 Adopt a regular spraying regime to protect your plants before the problem begins. It's a good idea to alternate the chemical that you use to prevent resistance occurring.
 Dig in plenty of organic matter at planting time and keep plants well fed throughout the growing season. Strong healthy plants will generally resist attack better those that are weak.
 Surround plants with a fresh layer of mulch each spring to smother any spores that have fallen around your plants and prevent them from getting on your plants.

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