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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

Motete T, Solís M, Hammerbacher A, Naidoo S. (2026) Gene Expression Profiling in Eucalyptus Associates Phenylpropanoid Resistance to Teratosphaeria destructans. Plant Pathology 10.1111/ppa.70207
van Heerden A, Pham NQ, Duong TA, Wingfield MJ, Wingfield BD. (2026) Draft genome sequence of Ganoderma philippii, a serious root rot pathogen of Eucalyptus in Southeast Asia. Australasian Plant Pathology 55:81. 10.1007/s13313-026-01159-1
Townsend G, Hill M, Hurley BP, Roets F. (2026) Native Scolytinae and Platypodinae beetle assemblages in indigenous South African forests and their co-occurrence with the invasive PSHB beetle. Journal of Insect Conservation 30 10.1007/s10841-026-00779-8
Botha I, Maduna SN, Hagen SB, Lall N, Berger DK. (2026) 3RAD-guided SNP discovery for species identification and conservation of the medicinal southern African tree Genus Greyia Hook. & Harv.. Ecology and Evolution 16(5):e73412, 1-29. 10.1002/ece3.73412
Balocchi F, Duncan G, Yilmaz N, Wingfield MJ, Paap T. (2026) The critically endangered geophyte Gladiolus aureus threatened by a wilt disease associated with Fusarium libertatis. Journal of Plant Pathology 10.1007/s42161-026-02227-7 PDF