Stop the press: The Polyphagous shot hole borer is in town.

The Polyphagous shot hole borer, Euwallacea fornicatus, or PSHB for short was discovered during a routine survey for tree pests and diseases in and around the South Africa’s National Botanical Gardens in 2017. The survey was conducted by International Plant Sentinel Network (IPSN) member Dr Trudy Paap working in collaboration with SANBI. This tiny 2mm-long beetle and its fungal friends have been grabbing the headlines since it arrived.

Boring through the bark of indigenous and commercial trees alike, the beetle creates a network of tunnels that provide a range of fungal species with wooden palace within which to proliferate. In return, the beetle’s larvae feast upon the fungal banquet. All at the tree’s expense! The problem comes with susceptible trees, where the fungus spreads like wildfire through the sapwood, causing tree mortality.

Should we be scared?

While PSHB has not been reported in commercial plantations in South Africa yet, it has been found infesting a small numbers of roadside wattle trees in the Southern Cape and a single roadside Eucalyptus tree in Sandton. PSHB’s recent arrival makes it almost impossible to predict the impact the beetle and its fungal friends will have on South Africa’s indigenous and commercial trees. Although the fact it has already affected more than 80 tree species and has been reported from eight of our nine provinces is cause for concern.

If we look at the impact PSHB has had further afield, there is good reason to worry.

In two American botanical gardens, Los Angeles and California, PSHB has infested more than 200 species of trees, including important crop trees such as avocado, macadamia, pecan, peach, orange and grape and a number of species native to South Africa: Cussonia spicata (cabbage tree), Calpurnia aurea (common calpurnia), Diospyros lycioides (monkey plum), Erythrina humeana (dwarf coral tree), Erythrina lysistemon (common coral tree), Schotia brachypetala (huilboerboon), and Melianthus major (honey flower).

As a result, scientists are not ruling out the possibility that plantation trees could be affected, which is why researchers at FABI are working towards a better understanding of the distribution and host range of this potential pest in South Africa, as well as investigating potential management options.

Ambrosia Beetle Working Group was formed at a meeting between FABI researchers, Department of Agriculture, Forestry and Fisheries (DAFF), Johannesburg City Parks officials, and other interested parties. The purpose of this group is to coordinate research efforts, monitor and consolidate data on the spread of the beetle. This includes collating host tree reports in the country, investigating possible control strategies, and advising government bodies, industry, and the public on the treatment of infested trees and wood.

A cause for concern?

Currently, there is only one chemical product registered for treatment against PSHB in South Africa, with varied results. This is a huge cause for concern, which is why the Department of the Environment, Forestry and Fisheries, DEFF, formerly Department of Environmental Affairs (DEA) is in the process of declaring PSHB an invasive pest. The Registrar, formerly DAFF, has called for the submission of emergency registration of chemical treatments under Act 36.

Taking a proactive approach

Government has established a national steering committee with interested and affected parties participating, which includes FSA Research and Protection Director Ronald Heath, as well as a number of FSA’s research partners.

Want to read more?

Make sure you keep abreast with PSHB updates on the FABI website.

Photo: Forestry and Agriculture Biotechnology Institute, University of Pretoria

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