Local tree protection specialists recently identified two diseases appearing for the first time in South Africa’s commercial forestry sector. Research is under way to understand what impacts these may have on infected Eucalyptus trees.
By Lloyd Phillips, senior journalist at African Farming and Landbouweekblad
South Africa’s commercial forestry sector is urged to be on the lookout for and to report the presence of two fungal pathogens recently identified on Eucalyptus species in different parts of the country.
Brett Hurley is a professor at the University of Pretoria’s Forestry and Agricultural Biotechnology Institute (FABI) and holds roles in other national and international forestry protection research entities. He reports that routine diagnostic clinic sample screening by the university’s Tree Protection Co-operative Programme confirmed Suberoteratosphaeria suberosa on mature Eucalyptus trees in the KwaZulu-Natal Midlands, and Apoharknessia insueta on Eucalyptus cuttings in a nursery in Mpumalanga.
Dr Wilma Nel manages FABI’s Diagnostic Clinic. She explains that S. suberosa was identified as the cause of tan-coloured spots on leaves of mature commercially grown E. smithii trees. These spots become thickened and scale- or cork-like with age.
“This fungus is mostly reported to affect older foliage but can affect the younger foliage in severe outbreaks. With the current outbreak [in the KwaZulu-Natal Midlands], we observed foliage on the trees having an almost scorched appearance from a distance, as if fire had moved through the compartment [of trees],” Nel says.
She adds that S. suberosa has been reported in Australia, Brazil, Colombia, Indonesia and New Zealand.
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Nursery Reports Unhealthy Eucalyptus Cuttings
Nel says the Diagnostic Clinic received E. nitens cuttings from a commercial tree nursery in Mpumalanga. The cuttings showed symptoms of disease and decline.
These symptoms included rot occurring above the root collar, as well as callousing of the tissue and cankering in that area of the young plants. Discolouration was also found underneath the calloused and thickened tissue at the root collar.
“Not much is known about the symptoms and severity caused by A. insueta,” she says. “Although species in this genus have been reported as both leaf spot and stem canker pathogens, they are typically encountered in the field and not in the nursery.”
A. insueta has been reported in Brazil, Colombia, Costa Rica, Cuba, Mauritius and America.
Nel points out that although reports from these other countries to date generally do not consider S. suberosa and A. insueta as severe pathogens, South Africa’s forest protection researchers are not taking this as a given. For this reason, they will be conducting in-depth research in local conditions to independently assess the threat severity these two diseases pose.
Stakeholders in South Africa’s commercial forestry sector are asked to immediately report any suspected cases of S. suberosa and/or A. insueta by emailing Sandisiwe Jali, field extension manager at FABI, at sandisiwe.jali@fabi.up.ac.za
