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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

Kim JS, Lee W, Seo CW, Lee JW, Perera RH, Rho SM, Visagie CM, Houbraken J, Lim YW. (2026) A comprehensive assessment of Penicillium diversity in marine environments. Studies in Mycology 115:1–57. 10.3114/sim.2026.115.01
Jami F, Truter M, Pavlic M, Chen SF, Roux J. (2026) Identification of Botryosphaeriaceae species in the South African National Collection of fungi, including a novel species of Oblongocollomyces. African Biodiversity & Conservation 56(1):1-13. PDF
Vettraino AM, Bose T. (2026) Urban green spaces as emerging hotspots for Phytophthora diversity: a global synthesis of host associations, distribution and management gaps. Frontiers in Forests and Global Change 9:1872981. 10.3389/ffgc.2026.1872981
Burgess TI, Wingfield MJ. (2026) Unveiling a hidden menace: Invasive tree pathogens, less known but increasingly threatening Southern hemisphere forests. Annual Review of Phytopathology 64 10.1146/annurev-phyto-011325-100959
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