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

Abate BA, Slippers B, Wingfield MJ, Malan AP, Hurley BP. (2018) Diversity of entomopathogenic nematodes and their symbiotic bacteria in South African plantations and indigenous forests. Nematology 10.1163/15685411-00003144
Palmer M, Steenkamp ET, Coetzee MPA, Blom J, Venter SN. (2018) Genome-based characterization of biological processes that differentiate closely related bacteria. Frontiers in Microbiology 9:113. 10.3389/fmicb.2018.00113 PDF
Paap T, de Beer ZW, Migliorini D, Nel W, Wingfield MJ. (2018) The polyphagous shot hole borer (PSHB) and its fungal symbiont Fusarium euwallaceae: a new invasion in South Africa. Australasian Plant Pathology 10.1007/s13313-018-0545-0 PDF
Van den Berg N, Christie JB, Engelbrecht J, Aveling TAS. (2018) Callose and β-1,3-glucanase inhibit Phytophthora cinnamomi in a resistant avocado rootstock. Plant Pathology 10.1111/ppa.12819
Wilken PM, Steenkamp ET, Van der Nest MA, Wingfield MJ, De Beer ZW, Wingfield BD. (2018) Unexpected placement of the MAT1-1-2 gene in the MAT1-2 idiomorph of Thielaviopsis. Fungal Genetics and Biology 10.1016/j.fgb.2018.01.007