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Aphids in general

Silver fir woolly aphid (Dreyfusia nordmannianae)


Abies nordmanniana

Yellow needle, here on Abies nordmaniana, cannot be seen at a distance (Dreyfusia nordmannianae)
Photo: Magnus Gammelgaard


Silver fir planted as solitaire in the garden, can bee a good solution. The fresh green and soft needles are pretty and nice to touch.
The silver fir has many practicabilities; used for decoration and as a Christmas tree both outdoors and indoors and at the same time it is cheep to buy.
Silver fir is normally a very healthy tree, which rarely is infested by pests and diseases and therefore is easy to grow.
One of the pests, which sometimes can be, recognizes is the silver fir woolly aphid (Dreyfusia nordmannianae).



Symptoms

On newly developed shoot curly needles are to be seen. On the branches from last year you can see yellow needles, which after some time will drop.
The symptoms often can bee seen on trees that are more than one meter high and they are very harmful for growers of Christmas trees, because they often are to bee rejected.
In gardens, heavy attack can result in poor growth. On the other hand moderate attack normally can bee accepted.

Dreyfusia nordmannianae

On the shoot axis you can see the volley, egg-laying aphids. (Dreyfusia nordmannianae).
Photo: Magnus Gammelgaard




Dreyfusia nordmannianae

The overwintering females are laying their eggs close to the buds in the springtime. (Dreyfusia nordmannianae).
Foto: Magnus Gammelgaard




Dreyfusia nordmannianae

When the eggs hatches, the larvea are crawling to the new shoots . (Dreyfusia nordmannianae).
Foto: Magnus Gammelgaard


Description

If you examine the shoots (best if you are using a magnifying glass) you will often be able to watch the woolly aphids sitting on the main shoot axis.
On the needles perhaps you will see very small black spots, which are the newly hatched aphids. Later they also become woolly and starting to lay eggs.

Biology

As many other aphids on trees and shrubs, this one are changing host. This means that different stages of the aphid are to be found on other trees than A.nordmanianana. The silver fir woolly aphid has Oriental spruce (Picea orientalis) as the main host. This one is not very common grown here in Denmark, so most people believe that the sexual stage which are going on this species, is not very widespread in this country.

The asexual stages are developing on silver fir (A. alba) and nordman fir (A nordmaniana).
At springtime over wintering larvae are transferred into egg laying females.
When the temperature has risen sufficiently eggs are laid and 3 different kinds of aphids are developing.
1. Aphids on new shoot axis. 2. Aphids on needles. 3. Aphids with wings that are seeking for oriental spruce.

The spread of aphids goes on in different ways; the small larvae are able to crawl from one tree to another if the trees are planted closely. Birds, animals, machinery are also able to do the transportation.

Control:

Luckily this pest has many natural enemies. Lady bugs and different species of parasitoids are mentioned, but especially larvae from lacewings are very greedy consumers of silver fir woolly aphids.
However there will often be to few of those natural enemies, or they will be there to late and therefore not be able to reduce population to an accepted level. In those cases the following insecticides can bee used.


Active ingredients Commercial name More information
Thiacloprid
Pyrethrin I og II + piperonylbutoxid
Kaliumoleat		 Calypso
1) Spruzit Insektfri Total
Insektsæber-flere		 Bayer husoghave
ECOstyle A/S
Egne sider




To achieve a good result, it is important to make an early spray in the spring, when the eggs are hatching. Be aware of the mineral oil. Under certain conditions it can make some scorching of the needles.

In forestry insecticides from the group of synthetic pyrethroids are used.

If you want to read more about aphids i general. Visit the: Ahpid site