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.

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Phasha MM, Wingfield BD, Coetzee MPA, Santana QC, Fourie G, Steenkamp ET. (2017) Architecture and distribution of introns in core genes of four Fusarium species. G3: Genes|Genomes|Genetics 7(11):3809-3820. 10.1534/g3.117.300344
Chen SF, Liu QL, Li GQ, Wingfield MJ. (2017) Quambalaria species associated with eucalypt diseases in southern China. Frontiers of Agricultural Science and Engineering 10.15302/J-FASE-2017173 PDF
Nel WJ, Duong TA, Wingfield BD, Wingfield MJ, De Beer ZW. (2017) A new genus and species for the globally important, multi-host root pathogen Thielaviopsis basicola. Plant Pathology 10.1111/ppa.12803
Aylward J, Wingfield BD, Dreyer LL, Roets F, Wingfield MJ, Steenkamp ET. (2017) Contrasting carbon metabolism in saprotrophic and pathogenic Microascalean fungi from Protea trees. Fungal Ecology 30:88-100. 10.1016/j.funeco.2017.09.002
Wingfield BD. (2017) South Africa can’t afford to see its universities pitch over the precipice. The Conversation PDF