Oak Tree
By Nomis58
United Kingdom 
I have an oak tree at the other side of my garden fence and each year at this time acorns drop into my garden, however this year whilst there are a few acorns there is an abundance of knobbly and hard knotted items falling from the tree.. Are these diseased acorns and if so has the tree become diseased.
16 Sep, 2008
Answers
If the acorns are shaped rather like little rosettes then your tree has been attacked by a new pest in Britain, the European oak gall wasp. I would say that about 90 percent of the acorns which have fallen from the trees on our lane have been attacked this way. The acorns are useless as far as producing new trees are concerned.
16 Sep, 2008
An attack on the fruit in the early stages.
It is only on the acorns, no need to worry about the tree.
You may also have oakapples.
16 Sep, 2008