INSECT GALLS
By Missprimmy
United Kingdom 
Hi,
I have a 3-4 year old pot grown oak tree which has developed these berry like growths.
I believe they 'insect galls'. Will they harm my tree, if so, how do I get rid of them.
Your help & advice will be very much appreciated.
5 May, 2014
Answers
the gall is the plants wound response. so the damage has been done. if they bother you then remove them. These are called oak apples and don't do any harm to the tree.
5 May, 2014
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There are over a thousand different insects, mites and fungi that cause these galls, and some of them are actually beneficial to the tree.
Insect galls don't usually do much harm to the tree unless you have a lot of them and they take too much nutrients from the tree. They are just unsightly.
You could use a spray, but once they are established getting rid of them is difficult as spraying them is usually carried out as a preventative measure before they take hold.
5 May, 2014