GEORGE NEWS - There are no quick fixes for the eradication of the destructive beetle that has almost certainly invaded the historical oak trees in York and Meade streets in George. "There has been no breakthrough with any chemicals and scientists still have many years of research ahead of them."
So said Prof Wilhelm de Beer, associate professor with Forestry and Agricultural Biotechnology Institute Academic & Science (Fabi), refuting a rumour that an effective poison has been found.
During his visit to George and the Garden Route in April, he took tree bark samples and this week he confirmed that the plane tree in Doneraile Square was infested. The old giant has since been removed. During that visit, Fabi's Dr Trudy Paap took note of the oak trees in George and said the infestation in George seems worse than in Knysna. De Beer said this week that the George Municipality has been one of the more active municipalities in that it has created an awareness of the beetle and placed signage on our big trees warning the public of possible falling branches.
Paap, who discovered the beetle presence in botanical gardens throughout South Africa in 2017, said the infestation has been confirmed in Durban, Hartswater,Bloemfontein, George, Knysna andJohannesburg. "At the moment we can't really predict how this beetle infestation will play out, as we do not want to cause panic and also because we are not sure if every infected tree will be killed."
In an article published on 30 August in George Herald sister newspaper Knysna-Plett Herald, Paap said the situation in George appears to be more serious. "There are a lot of old oaks lining George's streets that are close to death because of the beetle. The municipalities of George and Johannesburg are already facing removal of hundreds, potentially thousands of dead and dying street trees."
The PSHB beetle borer was discovered in 2013 in Knysna and in Canada and since then, research work has started finding ways of halting the little insect and the symbiotic fungal food it feeds on. ThePolyphagous Shot Hole Borer (PHSB)is an ambrosia beetle native toSoutheast Asia.
(Source : www.fabinet.up.ac.za)
The beetle has a symbiotic relationshipwith the fungus Fusarium euwallaceae, which serves as a food source for theadults and their larvae. In susceptibletrees thefungus causes Fusarium die-back, which can lead to branch die-back and treedeath. The beetles can attack a wide range of exotic and indigenous trees in urban, agricultural and natural landscapes.
The PSHB is not able to complete its life cycle on all of the tree species it attacks. Those the beetle is able to breed on are referred to as 'reproductive hosts'. Important reproductive hosts include species of oaks, maples, willows and coral trees, avocado and castor bean.
Plea for environmentally friendly solution
Ruth Fair from Mossel Bay, wife of the late biocontrol pasture consultant John Fair, is concerned that biocontrol interventions cannot be found sooner to save the proud old oaks of George. Ruth said that for many years she edited the articles her husband wrote for Farmer's Weekly advocating the use of biological insect control.
Ruth pleaded that an environmentally friendly solution should be found to deal with the PHSB borer, because going the chemical route may well have dire consequences for bees and birds.
Her husband had travelled to the US for research, where studies had shown that plants and trees under stress were more likely to be targeted by insects. In an urban area where oaks have their root systems compacted and encased by cement, they are undernourished and therefore stressed. Ruth said the oaks should be given Seagrow as it has a strong smell and is likely to act as an insect repellent whilst simultaneously providing the necessary nourishment. "The oak trees' root structures should be fed with compost and other organic food to strengthen their immunity against opportunistic fungi and beetles."
While Prof Wilhelm de Beer agreed with Ruth's theory that the immunity of trees are compromised when under stress, he said the suggestion made to leave food scraps on the trunks of oaks to draw the beetles to the surface to be eaten by birds is not viable. "The beetle lives solely on its symbiont fungus.
Instead, a well-researched solution will have to be found. Unfortunately, there are no quick solutions to this problem. Although the Fabi team is small and under-resourced, a US team has been working on finding a solution for many years already. An outcome that does not have negative consequences for the environment would be the ultimate one."
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