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Page 3

Garden Plant Disorders.

Pests and diseases of shrubs and trees

   
 
         Pests can be troublesome at  any time of the year, but in early summer it seems sometimes that the entire greenfly population has descended on your garden. Unhealthy plants which are struggling for survival in poor soil  always seem to suffer. So it follows that healthy plants should be able to withstand most pest attacks.
 
BUFF-TIP  MOTH
  • Symptoms:   Branches suddenly look bare as the leaves have all been eaten.
  • Shrubs  and trees affected. All deciduous species.
  • Treatment: When the caterpillars become active, spray with Bacillus thuringiensis  or an approved insecticide  containing  derris or pyrethrins.
CAPSID BUG
     All ornamentals are vulnerable.  The plants look as if they are riddled  with lead shot.
DUTCH ELM DISEASE
  • Symptoms:   This disease caused the disappearance of most elms in southern England, Wales and the Midlands and has spread into Scotland. The leaves  change  colour,  turn yellowish and dry up. First the branches, then the tree withers and dies.  The bark is covered in brown blotches and peels off. A cut branch will reveal a brown ring at the centre.
  • Tree affected: Elm.
  • Treatment:  There is no remedy.  Only cutting down and burning affected trees will limit the spread of the disease.
ELM LEAF BLIGHT
  • Symptoms:  In spring and summer, leaves are pierced with longish holes. Some leaves are covered with mould.
  • Tree affected:  Elm.
  • Treatment:  There is no cure. To prevent spreading, collect and burn infected leaves.
FIREBLIGHT
  • Symptoms:  Leaves crumble and look burnt. The bark splits and exudes a whitish ooze, with the inside tissue turning red. Contamination of neighbouring trees is swift.
  • Shrubs  and trees affected: All members  of the Rosaceae family,  such as hawthorn, cotoneaster,  pyracantha.
  • Treatment: Prune  out infected growth to healthy wood and spray  with a copper-based fungicide.  Disinfect  tools after use.
FROGHOPPER 
     Light yellow or white mottling  on leaves is caused by the bites  of this insect.
FRUIT  FLY  
    These flies can  affect many species,  including beech, gleditsia,  hawthorn, holly willow.
GALL  MITE
  • Symptoms:  The underside of infected leaves are covered  in white spots  that turn brown. The leaves blister  and become covered  in red galls.
  • Shrubs  and trees affected: Birch,  maple, beech, walnut, elm, lime.
  • Treatment:  Cut off and burn the affected leaves.
 
Gall-mite
 
 
Gall-wasp
GALL  WASP
  • Symptoms:  The undersides of leaves display  small, flat reddish galls that contain larvae. Acorns  carry  a wrinkled gall on the side of the cup. The affected buds  turn  pinkish and then drop off.
  • Tree affected:  Chiefly oak.
  • Treatment:  No treatment  is necessary as this insect  does not harm  the tree.  The galls protect  the larvae, making them difficult to reach.
HAWK  MOTH
  • Symptoms:  Leaf edges  are chewed,  especially in summer.
  • Shrubs  and trees affected: Many ornamental  species.
  • Treatment:  Remove  the large caterpillars  by hand.
LEAF  BEETLES
  • Symptoms:  In spring and summer,  leaves are pierced with holes,  although  the veins  are unaffected. Leaf tops may also be cut off and look shrivelled.
  • Shrubs  and trees affected:  Elder,  lavender,  poplar,  willow.
  • Treatment:  Where practical, pick off adult beetles.
LEAF BLOTCH
  • Symptoms:  Grey swellings with brown edges  appear  on infected leaves. The marks grow larger with the centres turning red and drying up.
  • Shrubs  and trees affected: Chestnut, vine.
  • Treatment:  There is no cure for this disease.  Collect  and burn infected leaves  and pruning's .  Improve  the drainage around  affected plants  and feed regularly  to aid recovery.
 
 
Leaf Blotch
LEAF-CUTTING  BEE
  • Symptoms:   The margins  of leaves are cut out in circular shapes  with regular  contours.
  • Shrub affected:  Rose.
  • Treatment:  The damage  is more  unsightly  than  harmful to the plant. Treatment  is not necessary,  especially  since the leaf-cutting  bee is a pollinator.
 
Leaf Gall
LEAF GALL
  • Symptoms:   Tumours  appear on leafy stems, often around the veins.  These roundish swellings  have a white covering that turns brown and shrivels.
  • Shrubs  affected:  Azalea, rhododendron.
  • Treatment:  Cut off and burn affected parts. Spray  with  a copper-based  fungicide.
 
Prevention

'Fruit Fly'
 
 It is best to destroy all damaged fruit to break the cycle of infection. Remove fruit from trees that have dimples or that are weeping clear sap. These are signs that eggs have already been laid in the fruit.  Feed the fruit to poultry or place the fruit in a sealed plastic  bag. It is better to strike early than picking rotten fruit from the ground because of the possibility of the maggots having left the fruit to pupate.
In an ideal world it would be better to plant trees that are not prone to fruit fly. It will be easier to for year round management with dwarf or multi grafted fruit trees. If you  have poor quality or  diseased trees it would  be worth considering  replacing them with newer varieties.
If you wish to grow stone fruit, dwarf or espalier trees will make your fruit management far easier.
 
 
 
 
 
 
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