A reader wrote to us about some bumps on the leaves of his trees. Although the leaf bumps are only, well, bumps, the reader suspects that “it’s worms.” What precisely he means is unclear, but we suspect he means that either worms are causing the bumps on the leaves, or perhaps that the worms are somehow disguised as, or covered by, the bumps on the leaves. The reader also asked “how to get rid of them,” and again it isn’t exactly clear what this means because “them” is undefined. In any case, we’ll have to focus on the prior question – are the bumps on the leaves worms (or something else, like larvae or leaf galls?) – as this matter must be settled before there is any talk of remedies or elimination. A diagnosis always precedes a cure.
First, we should note that this question arrived over two emails sent several days apart, so we had to compile the two messages, which had different emphases. The first email stressed that worms might somehow be behind the leaf bumps, and the second only mentioned the bumps, which can be seen in the following two photographs:
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Although the reader may not have been aware of this, the focus of the second email – on the bumps themselves – suggests an answer to his question, namely, the leaf bumps are only bumps, and they are not worms in disguise or anything like that. In particular, it appears that our reader has merely found leaf galls, or abnormal growths that look like little bumps, which commonly appear on tree leaves in the spring, precisely the time of year in which our reader wrote to us.
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Leafs galls make a tree appear sickly, at least to a lot of people, but in fact the small growths are almost never a cause for concern. They only affect the appearance of the tree and do not compromise the plant’s overall health, at least in most cases. It is the tree itself that produces the galls in response to insects (especially wasps) or mites eating its leaves. As leaves rapidly grow in the spring, creatures will begin to eat them, which causes the plant to produce growth hormones that in turn produce galls. Once the hormones have been stimulated, the galls will grow, even if the insects eating the leaves have moved on (which is very often the case by the time anyone notices the galls). So, galls merely indicate that the leaves of a tree have been eaten by some creature.
Again, the appearance of galls on your trees shouldn’t be particularly worrying because galls very rarely compromise a tree’s basic health. Moreover, once one notices the galls, nothing can be done, as the stimulus that gave rise to the bumps has happened long ago. Looking forward, you could potentially try to protect your trees by treating them very early in the spring, but this probably isn’t worth the trouble unless you have a serious and reoccurring problem.
So, to bring this back to our reader’s specific questions: the bumps on the leaves of his trees are very likely galls, and since galls are a mere cosmetic problem (and often a fairly minor one), they aren’t cause for concern. There is no way to “get rid of them” because of their sequence of growth, but perhaps our reader can tolerate the galls knowing that they aren’t indicative of some abnormal infestation. Their emergence is part of the annual patterns of nature. Galls are, at worst, galling, but not much else.