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.
- 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.
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.
- 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.
Light yellow or white mottling on leaves is caused by the bites of this insect.
These flies can affect many species, including beech, gleditsia, hawthorn, holly willow.
- 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.
- 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.
- Symptoms: Leaf edges are chewed, especially in summer.
- Shrubs and trees affected: Many ornamental species.
- Treatment: Remove the large caterpillars by hand.
- 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.
- 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.
- 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.
- 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.
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.