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Galls are abnormal growths on a plant that can have various causes, including viruses, nematodes, bacteria, fungi, mites and insects. Aphids, flies and wasps are some of the insects known to cause galls. Generally plants can tolerate galls with no obvious injury. However, a very high incidence of galls can damage and even kills plants.

Gall formers on eucalypts

The Eucalyptus gall wasp (Leptocybe invasa) is currently the only gall forming insect in South Africa which is considered a serious pest of plantation forest trees. This insect, which infests Eucalyptus, was accidentally introduced from Australia. It was first detected in South Africa in 2007 (and only in 2009 in forestry areas). The Eucalyptus gall wasp causes galls on the stems, petioles and midrib of leaves. Damage by this insect is particularly severe on younger trees, where the majority of leaves can have galls, resulting in severe leaf drop. In such cases, stunting of growth and possibly tree death can occur. The adult wasp is minute (about 1.4 mm), but the galls, which often contain multiple eggs of the Eucalyptus gall wasp, are easily visible. Severely infested trees have a gnarled appearance.

New Publications

Paap T, White D, Bose T, Burgess TI. (2026) Diversity and phylogeny of Phytophthora Clade 9, including descriptions of three novel species. Mycological Progress 25:29. 10.1007/s11557-026-02140-4
Li GQ, Slippers B, Wingfield MJ, Chen SF. (2026) Diversity, distribution and host range of Botryosphaeriaceae in China. Forest Pathology 10.1111/efp.70077
Joubert M, van den Berg N, Theron J, Swart V. (2026) Leaf bleaching is associated with extensive transcriptional reprogramming in avocado trees with sunblotch disease. Virology 620:110903. 10.1016/j.virol.2026.110903 PDF
Nzuza P, Schroder ML, Slippers B, Maes WH. (2026) Spectral responses to larval and artificial defoliation in Eucalyptus dunnii: Implications for UAV-based detection of Gonipterus damage. Drones 10(4) 10.3390/drones10040250
Six DL, Marincowitz S, Duong TA. (2026) Ophiostoma ipsi-confusi sp. nov. Six, Marinc. & Duong, a consistent symbiotic fungus of the pinyon ips bark beetle, Ips confusus LeConte. Symbiosis 10.1007/s13199-026-01135-9