Getting To Grips With Galls

Plant galls may be unsightly, but they’re no reason to panic!

- Paul Donovan

Abnormal growths in plants can usually be attributed to the formation of galls. Galls can form on any part of the plant, from the roots to stems, flowers and leaves, and usually appear when the plant has been attacked by bacteria, viruses, parasites, fungi, mites, nematodes or certain insects. Alternatively, they can often simply be an abnormal growth in the plant’s cell structure – a bit like cancer in a mammalian cell.

We notice galls because they appear as unsightly growths on the plant, and we immediately suspect them to be harmful. It is true that they are unsightly and that they interfere with the normal functioning of the plants growth, but seldom do they pose any real threat to the plant’s health, unless the growth is extensive. Leaves that suffer serious cover may be unable to photosynthesise and could eventually die and fall off. Also, growth beyond the point of a gall on a twig might stop, and some plants may exhibit stunted growth, because the gall is tapping into vital nutrients that the plant needs during the growing phase. If a large number of galls are present on a young plant it may suffer considerably more than a mature one.

Rather bizarrely, some galls can actually be quite attractive. A Cynipid wasp found in America produces a gall resembling pink and white fluffy candyfloss.

How are galls formed?

It would be beyond the scope of this article to cover all scenarios that may give rise to the formation of galls, so I will just give a brief overview of those resulting from interactions with insects, as these are more common.