Knopper galls and powdery mildew

As the acorns form on oak trees you may see some of them being DE-formed by the growth of a knopper gall, which looks almost like a pine cone.  (Mentioned this last year on October 10th.)

These galls are produced on acorns by the tree in response to a tiny gall wasp which spends its early life on a Turkey Oak rather than our native oaks.  After mating, eggs are laid in the early stages of acorn development and the wasp larva lives and feeds inside the gall.  The galls fall to the ground in autumn and in spring female only wasps emerge and find a Turkey oak to lay more eggs.  It's only been around in the UK since the 1950s and there was a boom year in 1979.

It's not thought to be much of a problem.  The gall destroys the acorn but there are always plenty more.

Another thing you may see on oak trees currently is powdery mildew.  This is caused by a fungus and is more frequent in mild overcast summer weather.

Just two of the organisms which like to take advantage of the oak tree.