Damage

Tree disease and death can arise from a multitude of factors, including living organisms (biotic) such as insects and fungi, or abiotic agents such as frost, drought and chemical damage. In order to adjust management practices appropriately, it is crucial to correctly identify the cause of damage to trees. The following section summarizes some of the most common causes of tree damage or disease and provides guidelines for distinguishing between the different categories of damage, disease and decline.

Distinguishing between causes of tree health problems

Abiotic Biotic
Non-living (eg. chemicals, frost, drought) Living (Fungi, bacteria, insects)
Absence of host specificity Often host specific
Non-infectious Infectious (can spread from one tree to another)
Usually a gradient visible (worst near source of origin, with impact gradually becoming less as distance from source increases)
Damage usually of same age/phase of expression
Often random in the plantation
Damage often at different stages of development as pathogen/pest spread from one tree to another

Signs and Symptoms

Disease and pest problems may be identified by observing certain signs and symptoms of infection / infestation. Signs include the presence of fungal fruiting bodies, or egg capsules of insects, while symptoms include leaf spots, defoliation, cracking of stems, wood stain etc. Characterizing the type of damage and the visible signs is useful in making accurate diagnoses.

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