What are those ugly things on my oak tree?

29 May 2009 by Shari.

We’ve all seen them. Those growths on our oak trees that look like a tumor of some kind. But what are they and should I be worried about them? They probably look something like this picture.

Most may not be as pretty as this one and sometimes there are a cluster of these little balls all in the same place. As a matter of fact, these may not be small balls at all, but instead can be varying sizes up to an inch in diameter. These are oak galls.

Galls on trees are caused by insects, such as certain small wasps (cynipids) aphid species, flies, phylloxera, psyllids, thrips, moth caterpillars, beetles, and mites. Galls make the tree look unpleasant even unsightly. However, they do not damage the tree other than disfiguring it. 

You probably start to notice Galls in spring. The actual Gall itself is full of larvae and eggs that emerge from the Gall in a few weeks. The life cycle begins again and the females oviposit eggs on twigs and branches. These eggs remain dormant for 3 to 5 months.

Galls on oak trees are common and noticeable but do not cause damage. The best advice is to ignore these little suckers!

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