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Aphids in general

Rosy Apple Aphid (Dysaphis plantaginea)

Curling shoots and leaves are often the first symptoms from aphid attack.
Especially the rosy apple aphid is causing serious damage on apples. (Dysaphis plantaginea).
Photo: Magnus Gammelgaard

Later the leaves are beginning to die. . (Dysaphis plantaginea).
Photo: Magnus Gammelgaard

Aphids on trees and shrubs are to be seen everywhere. Normally aphid attack only will lead to a little bit of leaf curling, or a small grade deformity or stunting to be seen on the host plant.
It is different with the rosy apple aphid where the damage often is much more serious. This was seen in Denmark at the growing season 2004. All over the country heavy attack was observed on different species of apple trees.

Not only did the new shoots get withered leaves and the growth stunted, but also the small fruits were totally destroyed.

Also in large orchards it was seen, that the yield was totally absent.
However it is seldom that that an aphid attack is developing so violence and it can only be related to the optimal climate conditions in the autumn where the eggs were laid and the climate in the spring.

If you do unroll the leaves, you will see the rosy, waxy aphids (Dysaphis plantaginea).
Photo: Magnus Gammelgaard

Symptoms:

Heavy leave curling on newly developed shoots, is the first symptoms on an aphid attack. It is not necessary with a lot of individuals, before the leaves are beginning to curl. This curling protects the aphids from outside climate influences. Influences that are not favourable for the aphids.

Like other aphids this species also excrete excess sap called "honeydew", which provides a medium for growth of black sooty mould.
These dark fungi are reducing the photosynthesis and together with the honeydew are giving the leaves an anaesthetic, sticky surface.

Only the ants are happy for the honeydew and they will do nearly everything, to protect the aphids against any unfavourable influences including natural enemies.
Often you can see ants attacking ladybugs when they are getting close to the aphids.
Depending of the variety of the apple tree different reddish deformities is to be built. At heavy attack over a long period, you will see that the leaves developing and growth are totally stunted.
If the aphids are feeding on the new developed small fruits they will be deformed, early mature and totally without taste. Heavy attack also leads to the decline of next years flowering at the yield will be considerable smaller.

Fruit affected by rosy apple aphid. (Dysaphis plantaginea).
Photo: Magnus Gammelgaard

Biology:

The rosy apple aphid over winters as eggs on apple branches. The eggs laid in the fall are yellow and about 0,5 mm long. After about 14 days they begin to get darker and later they are totally shining black. If you use a magnifying glass you will able to see those eggs during the winter even thou they are hidden behind bud scales and other hiding places. However, at that time it is impossible to distinguish between eggs from the rosy apple aphid and those from the green apple aphid.

The eggs are hatching at the time just before beginning of flowering. The newly hatched nymphs immediately begin to such on newly developed leaves and buds. After 4 molts the wingless females are giving birth to live young without being fertilized by males ("virgin birth").

If the condition for food uptake is bad, female aphids with wings are born. They can fly away to other apple leaves. Every female produces in average about 150 to 200 nymphs and because the developing time for one is only 2-3 weeks it can lead to a rapid build up of generations.

It is quite normal for aphids to have more than one host. The rosy apple aphid are chancing host in the late July. Aphids leave the apple leaves to colonise plant from the group of plantain (Plantago) or dock (Rumex).

In autumn they are coming back to the apple trees where males are born and mating can take place. The females lay their eggs at the branches to secure the next years generations. It has been shown that the weather conditions in the autumn are essential for the aphids attack in the next season. A very wet and rain full autumn result in a small number of eggs followed by a slight attack the next season.

Precautions:

Natural control. A great amount of natural enemies are able to regulate the population og rosy apple aphids. Ladybugs, parasitic wasps, larvae of hover flies and lacewings, are the impotent ones. Take a look at Aphids in general.
It is therefore important that the garden consist of a great amount of different plant species to benefit the natural enemies.
Water. With a powerful water jet from a garden hose, it is possible to wash down a lot of aphis from the leaves.
Pruning. New shoots, which have been heavily infected, can be removed and destroyed.
Host. Removing the secondary host (plantain and dock). However you have to calculate that the aphids are able to fly a considerable distance or be transported by the wind.

Plant protection:

Chemical

Active ingredients	Commercial name	More information
pyrethrin cypermethrin	Spruzit InsektFri Total Maladan insektmiddel	ECOstyle A/S Bayer Garden

Paraffin oil and other vegetable oil, should be used in the springtime, before flowering to damage the winter eggs. There is a risk that the leaves can be damaged by the use of oil.
The use of chemical pesticides, normally damage the natural control, because the beneficial insects also are affected.

In orchards the following pesticides also are used:

Mospilan (acetamiprid).
Karate (mbda-cyhalothrin)
Fastac 50 (alpha-cypermethrin)
Cyperb (cypermethrin).
Movento (Spirotetramat 100 g/l )

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