APPLE WOOLLY APHID — Eriosoma Lanigerum
Apple woolly aphid can also be known as American blight and is a sap sucking insect. As the name suggests, Apple woolly aphid is a common pest of apple trees including crab apples but can also affect cotoneaster horizontalis, pyracantha, mountain ash, hawthorn, and elm.
Signs of infestation to look out for are colonies of aphids during the summer on tree trunks and branches with these aphids being covered in a white waxy fluff, making them pretty easy to detect. Cankers or swellings may also appear on the bark which can then split in frosty weather. These swellings are caused by chemicals being secreted into the plant by the aphids as they feed. While feeding, woolly aphids excrete honeydew or plant sugars which cover the leaves of their host plant. This honeydew then becomes infested with a black sooty mould.
The adult woolly aphids are of an elliptical shape and up to about 2mm in length. Woolly aphids do not lay eggs but spend the winter on their host plants in cracks and crevices under loose bark and around previous feeding areas as immature nymphs. These young nymphs do not produce a soft covering.
Once spring arrives the woolly aphids become active, start sucking sap and develop their soft cover. They can also give birth to up to five young a day, thus quickly producing large colonies, with infestation usually reaching its peak in mid to late summer. This is when some aphids will develop wings and fly away to find new plants to live on.
TREATMENT
Use products containing the chemical ingredients Pyrethrin or Pyrethroids as these compounds are useful in dealing with the woolly apple aphid.
To manage woolly apple aphids organically, encourage their natural predators for example ladybirds and hoverflies, into the garden by growing flowers which attract them and also providing winter shelter.
Check bark and tree regularly shoots for signs of aphids and spray with natural fatty acids or scrub with a brush and soapy water. A blast of water from the garden hose will help to knock some of the aphids off the plant which will reduce their number.
To help prevent woolly aphids in the first instance, hanging bird feeders in the winter months and in the spring providing nesting boxes, will contribute to attracting insectivorous birds to your garden. Planting daisy type flowers and especially yellow flowers in the backyard will also encourage the aphids, natural enemies, such as hoverflies and ladybirds to become regular visitors.
When buying new apple trees for planting try to source rootstock that is resistant to the woolly aphids.
POWDERY MILDEWS
Powdery mildew is a fungal disease affecting many different plants. There are several different varieties of the fungi with these individual strains preferring different types if host plants.
Affected plants range from rhododendrons, roses, honeysuckle, phlox, delphiniums and acanthus to name but a few with edible plants affected including apples, grapes, blackcurrants, marrows, peas, courgettes, strawberries, marrows and many others.
Signs to look out for are a white powdery coating on the leaves, stems, flowers and fruit of plants, with the leaves of some plants becoming distorted, while other leaves can turn a dark brown.
The fungi of the powdery mildew produce airborne spores which are spread long distances by the wind and due to their high water content they are still able to infect plants under parched conditions. Powdery mildews overwinter as dormant infections on fallen leaves or on green plant material until spring when they start releasing their spores again.
TREATMENT
Products containing any of the following chemical ingredients are all effective in dealing with powdery mildew: flutriafol, myclobutanil, penconazole.
To deal with powdery mildews organically, keep greenhouses thoroughly clean with a garden disinfectant and remove any unhealthy perennials in the autumn. This will help to prevent the infection spending winter on infected plants and thus releasing spores in the spring.
Any shoots or branches showing signs of infection should be pruned out immediately. Great care needs to be taken to prevent spores falling onto healthy shoots.
All infected material should be burnt quickly to avoid the spores being spread by the wind.
To help prevent powdery mildews in the first instance, to ensure proper air circulation and lessen humidity, avoid planting too closely together and thin out any crowded growth. Plants, especially those in containers need adequate water and to keep roots moist apply mulches during the spring and organic matter during the autumn. Avoid giving susceptible plants too much nitrogen-rich fertiliser as this just promotes sappy growth thereby making the plants more likely to be infected by the fungi.
FIRE BLIGHT — Erwinia Amylovora
Fire blight is a bacterial disease affecting apples, pears and related ornamentals including hawthorn and rose which typically occurs from late spring until the autumn.
Signs to look out for are blossom wilt, discoloured and wrinkled fruit and leaves turning a dark brown in colour and then dropping. As the infection spreads down the inner bark, shoots can shrivel up and die, and the outer wood can become a brown colour. Infections and cankers can also cause sometimes ooze a white slimy liquid.
Fire blight gets its name from the scorched appearance it gave to infected plants and was originally native to North American. Unfortunately, in 1957 fire blight was accidentally introduced into the United Kingdom where it became a notifiable disease, although this is now no longer the case for the UK mainland.
The bacteria spend the winter months in bark cankers until spring when the bacteria ooze from the cankers, this bacteria is then spread by insects, birds, garden tools and splashes from water to mention but a few. If conditions are suitable, the infection can spread rapidly leaving infected trees looking like they have been scorched by fire.
Luckily the United Kingdom is usually too cold at blossom time for diseases to arise, although if conditions are warmer later in the season, and the tree comes into flower for the second time, this is when the risk of infection can occur.
TREATMENT
Commercial chemical control for fire blight is not available at this moment in time.
To deal with fire blight organically, only saw or prune into healthy, undamaged wood and sterilise all tools used for removing infected material. If more than one branch needs to be removed, any tools used for removing branches should also be decontaminated before moving on to deal with the next branch.
All removed infected leaves, branches and flowers should be burnt.
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