Aphids an Adelgids


Aphids are probably the best known pests of plants on the planet.

The damage they cause is twofold. Firstly they suck the sap from the plant, inhibiting its flow to and from the growing shoots and not allowing leaf development. The leaves it should be remembered produce the sugars the plant needs to grow. Secondly they wound the plant, allowing fungal attacks.

Many people will baulk at the idea of spraying insecticides because they kill friendly insects as well as harmful ones. This is undoubtedly true with plants in the ground, however potted plants are to a large extent isolated from the environment, so spraying will have a minimal effect.


The life cycle of the Aphid is really complex. if indeed you can use the term life cycle, normally associated with an individual.

As the year progresses the type of aphid and its method of reproduction alters dramatically. The first generation emerges from eggs, overwintered in bark, they reproduce asexually, that is to say they give birth to live young without mating. This allows a rapid build up of the population. They are wingless. All of these qualities apply to the second generation. Within the third generation, some are born with wings, rapidly spreading to plants both near and far. Yet again this generation reproduce asexually.

The next generation produces both winged females and males, mating and laying the overwintering eggs.

Woolly Aphids on an Apple tree


Aphids up close


Adelgids

Adelgids are close relatives of aphids and can be treated in the same way.

Spraying with an insecticide is really the only way to hold them in check. A good preventative is to spray your deciduous trees with one of the many commercially available winter washes. As the name implies it's sprayed on overwinter and will kill any eggs on the tree. Personally I only use them on my deciduous trees, as they tend to be based on 'Tar oil' and I don't like the idea of applying an oil-based product onto trees in leaf.


Allen. C. Roffey 12:36 17/09/2008