Monday, 3 December 2018

Lovely topic: Bacterial Canker

A number of cherry trees in Daventry - and doubtless elsewhere - are poorly. Gaping wounds develop in the trunk of the tree, probably initiated by a wound which may at first have been quite innocuous.
This cherry tree in Southbrook, Daventry, was in a bad way.
3 December, 2018

Unfortunately the wound may become infected by bacteria, splashed perhaps from the leaves, developing into bacterial canker. Gum is often then exuded, sometimes copiously, to form a sticky amber or brown coloured blob. The gum may be produced to try and protect or seal off the wound

A closer look at the wound shows that it is bleeding a sap which will
later form a gum. Note the spider web.

I have noted several examples lately and one tree I saw this morning at Southbrook, Daventry, was in a bad way, probably dying.

But, unless you are a tree, not all is bad news. The wounds seem to attract a range of fungi and insects, the latter often boring into the wood. Death Watch Beetles (Xestodium species), such a pest of old furniture, doubtless exploited this habitat for countless millennia before humans unwittingly provided them with fresh possibilities.

The crevices also become a home for such creatures as woodlice and spiders. The second photograph clearly shows the lacy, blue-grey web of an Amaurobius species. These spiders are coloured in a pattern of light and dark brown and if they keep still they can be difficult to spot. In this particular situation they probably dine on a steady supply of insects attracted to the cankerous wound nearby.

Many trees exude gum as a response to wounding and in some countries the trees are deliberately damaged to initiate this, with the resultant gum being harvested. When as a youth I worked in the shoe industry where considerable use was made of Gum Tragacanth, collected from Astragalus tragacanthus and its relatives. It was always referred to as 'gum dragon' and I seem to recall that it is also used somehow in cooking (cake-making?) but I have no idea how or why.

Definition.   Pain aux raisins -   A nasty ache in the sultanas


No comments:

Post a Comment