Thursday, 25 August 2016

Byfield Pocket Park, late August

Another visit to Byfield Pocket Park - an almost weekly event it seems. I passed clumps of Stinking Iris, Iris foetidissima, all of which seemed to be infected with the rust Puccinia iridis. Like most (all?) rusts, this organism has alternate generations, with the other host uncertain, although common nettles are suspected. Some irises are immune to this disease, but it seems that the Stinking Iris is particularly susceptible to attack. 
Leaves of Stinking Iris under attack from Iris Rust.
Byfield, Northants. 24 August, 2016

These rusts are a terrible problem, with outbreaks of the related Wheat Rust, Puccinia triticina, regularly devastating crops in the tropics, particularly in India.

Nearby another plant was under attack, but from a quite different source. Broad-leaved Dock, Rumex obtusifolius, is a very common species of dock, and is indeed quite a serious agricultural pest. Some measure of control is afforded by the anthomyid fly, Pegomya solennis.
As the picture shows, the larvae of this insect cause a large blister-like patch to develop, often covering 50% of the leaf. It won't kill the plant but will debilitate it and perhaps lead to lower seed production.

Broad-leaved Dock under attack by Pegomya solennis  Byfield
Pocket Park. 24 August, 2016
We have about 61 species of Pegomya known from the U.K. and a range of plants may suffer serious attack from other members of this genus.

There are some days which seem too hot even for insects and today was one of those days. A few butterflies were about and Small Whites were common. A Speckled Wood fleetingly rested on foliage, flicked its wings and flew off.

Speckled Wood on sycamore foliage. Byfield Pocket Park.
 24 August, 2016

One of the 'Blues' was visiting bramble blossom. It refused to open its wings; these creatures don't always as you would wish and I was reminded of a note written by Kenneth Williams in his notorious diaries: '...went to see Ring of Bright Water which was about as bad as you can get in movies. Even the otter was amateur'. However, despite it being shy of the camera it is clearly a Holly Blue, Celastrina argiolus, and appears to be a male.

A solitary Horse Chestnut stands near to the pocket park entrance. Isolated it may be but Horse Chestnut Leaf Miners had sought it out and the leaves were characteristically disfigured. The leaf miner in this case is a tiny moth, Cameraria ohridella.

Horse Chestnut foliage mined by Cameraria ohridella. Byfield
Pocket Park. 24 August, 2016
Although it was first recorded in Britain as recently as 2002 its spread has been rapid. A friend recently remarked that the Sweet Chestnut, Castanea sativa, seems unaffected. In fact the Horse Chestnut, Aesculus hippocastanoides, and the Sweet Chestnut are completely unrelated so one would not expect the latter to be attacked.

I suspect the Horse Chestnut Leaf miner is here to stay as eradication seems very unlikely.

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