Could Small Beetles Threaten South African Agriculture?

World-wide invasive species pose a significant threat to agriculture and food security. The recently detected Polyphagous Shot Hole Beetle (PSHB) currently poses a big threat not only to South African farmers but also our urban forests. The beetle was first detected by Dr Trudy Paap in the KwaZulu-Natal National Botanical Garden in Pietermaritzburg in February of last year. Since then the beetle has been found as far as the Eastern and Northern Cape and Gauteng regions.

PSHB is indigenous to southeast Asia and approximately 2mm in length. With it, it carries a fungus that poses the real threat to the trees it infects. Once the beetle has bored its way to the core of the trunk it deposits the Fusarium euwallaceae fungus which starts to multiply and cut off the tree’s vascular system. The vascular system is needed for transporting nutrients and water throughout the rest of the tree and its branches. With the vascular system cut off, the tree becomes deprived of water and nutrients and it starts showing signs of dead leaves and branches. Eventually the infested tree will die.

Trees that have been infested show the following signs:

• Dead branches
• Visible exit or entry holes in the bark of the tree that look like shotgun holes
• Discharge at the entry or exit holes in the form of resin, sugar volcanoes and wood frass

The PSHB has wreaked havoc around the world and caused significant damage in Colifornia, North America and Israel in the Middle East. The detection of PSHB in Hartswater in the Northern Cape is especially concerning. According to the Department of Agriculture, Forestry and Fisheries, pecan trees from this area show infestation.

If the already widespread infestation in Johannesburg serves as an indication, there’s reason for much concern. Andrea Rogen, co-director of the Johannesburg Urban Forest Alliance, says that some projections indicate that up to half a million trees in Johannesburg are infected. Johannesburg is estimated to have between 6 and 10 million trees, making it one of the largest urban forests in the world. If PSHB is to spread to agriculture the effects could be devastating to those who farm with avocado, grapes, pecan, peach and orange.

South Africa produces around 125 000 tonne avocadoes, 2 708 767 tonne table grapes, 2 500 tonne pecan nuts and 2 000 000 tonne citrus a year. More than half of the produce is exported and contributes to South Africa’s growing economy.

Remitto together with its registration partner DNA Plant Science, are currently conducting various trails on this insect and the consequential damages of the fungi. We believe that with the current products under development that are at our disposal, we will be able to introduce a solution shortly. 

Should you suspect a tree to be infested by PSHB we urge you to contact the Department of Agriculture, Forestry and Fisheries. Until a viable solution is found, trees that are infested should be removed and disposed of responsibly. Residents of urban areas can report suspected infestation by using the Tree Survey, treesurvey.co.za.