Today’s visit to the great outdoors started much as usual, with a visit first to the Botanic Gardens in Durham and then to Crook Hall and Gardens to look at beautiful and interesting flowers.
Tree mallow at Crook Hall
However, whilst admiring a lovely mature copper beech tree near the top of the garden, Sue and I found some interesting things on the leaves. The first thing we spotted was the red blotches on the leaves below – they look a bit like someone has scattered red glitter on the leaves – shiny, and rough to the touch.
I’m sure this must be some kind of leaf-spot fungus, but haven’t been able to find out any more about it yet.
The other pests beneath the leaves were much less subtle – a mass of tiny aphids amongst waxy white threads. These are known as woolly beech aphids (Phyllaphis fagi), for obvious reasons.
Woolly aphids of a range of ages and sizes underneath a beech leaf
Like other aphids, these are sucking sap from the phloem tubes of young leaf veins – siphoning off the products of photosynthesis intended for plant growth. The aphids secrete waxy white fluff to help protect themselves from desiccation and predation, as well as the usual honeydew, which makes the leaves sticky.
For most of the summer the wingless aphids (all female) reproduce rapidly and asexually, producing more live young. Anyone with roses will know just how little time it takes a few aphids on a plant to turn all the new growth into a sticky mass. A newborn aphid will be able to reproduce within about a week and can then go on to produce up to five offspring a day for up to 30 days!
Then, in mid-summer, winged forms develop (still female) which fly off to find new host trees. At some point, some of the offspring they produce will develop into male aphids and sexual reproduction takes place. Fertilised eggs are laid around buds and in crevices in the trees’ bark in the autumn, to over-winter. The eggs finally hatch to coincide with the growth of new, spring leaves which will provide the new generation with a plentiful supply of food.