Knysna’s Oak Trees are dying

Posted by on March 5, 2015

Knysna's oak trees are dying

Pieter Boshofff of Singenza Tree Felling is leading teams to systematically evaluate all the oaks in Knysna and to apply risky surgery wherever they can rescue a part of a tree.
KNYSNA NEWS – Around 200 years ago George Rex ordered many bags of acorns from India to be planted alongside the roads of Knysna.
The story is told that these Indian acorns came from English Oaks that had been planted in India by the English many years before.

The grand trees that line many of the streets of Knysna would seem to date from that era. For many years they have proudly watched the town grow while they provided a canopy of shade in Summer and great beauty all year round.

But a dangerous enemy of the oak has infiltrated our town, and has succeeded in spreading a pestilence so deadly that ultimately all the oak trees will probably die within the next decade.
This evil destruction is being caused by the alien ambrosia beetles. The small beetles bore into the trees, leaving sawdust in their wake. They bore through the bark to the sapwood where they reproduce. Here they create huge reproduction galleries which weaken the tree and can lead to catastrophic damage to the trees.
For the last few weeks, Knysna residents have become aware of teams of men in orange jackets and trucks with tall cranes setting up warning tape around the oak trees, and the sound of chainsaws have become a common sound during the day.
Last year, residents were outraged at the prospect of all the oaks being chopped down. In response, the municipality decided, at great expense, to implement a programme of cutting off branches which are deemed potentially dangerous, while allowing the rest of the affected trees to stand proudly for a short while longer. Unfortunately, trees which are too badly infected must now be chopped down.
So who are these men who have taken charge of our trees? The Knysna Municipality has contracted Singenza Tree Felling to manage the culling process. They are one of very few companies in South Africa who can manage an undertaking of this nature. Led by a very professional tree surgeon, Pieter Boshoff, who trained in America, the tree teams are systematically evaluating all the oaks in Knysna and applying their high-risk surgery wherever they can rescue a part of a tree.
Due to the fact that the beetle is destroying the inside of the trees, many trees have become unstable and are no longer safe to climb up. Special trucks with mounted cranes are needed to reach the high branches where the necessary cutting is done. The teams use the experience gained from many years of cutting trees to prevent cut branches from falling randomly and causing damage. The teams have considerable rope skills and, in the case of more solid trees, they physically climb up the trees to cut the branches. It is very dangerous work – but Boshoff is proud of his workers, some of whom have been with him for 18 years.
Although we may regret the loss of the mighty oaks, there does not seem to be any alternative, and the municipality has evaluated all the options available to them. In the long term the trees which are cut down will be replaced by suitable indigenous species. The only sadness is that it may take another 100 years before they are large enough to grace our streets with the same stature as the oaks that lined the avenues of Knysna for such a long time.
* The long Summer that Knysna enjoyed in 2012/ 2013 is the most likely cause for the oak trees’ weakened, stressed state. The beetles are more active in warm weather which also promotes fungal fruiting, making the oaks an ideal target.
There is no treatment for ambrosia fungus. Best practice is to support the tree with additional nutrients (organic or slow-release nitrogen) and water to boost the tree’s natural immune system and processes. For healthy trees a watering programme will invigorate flow and prevent beetle ingress – this would not work in severely infected trees. Those trees must be cut and burned to reduce beetle population and spread capabilities. The best Knysna oak tree owners can do for their healthy oak trees is to support it with additional watering in dry times. Regular drip feeding is preferred to infrequent heavy watering sessions. Read more about this beetle at www.bekarutree.co.za.
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I’ve re-posted the blog above which appeared in the KnysnaPlett Herald of 5/3/2015  in the interest of all gardeners of Knysna.
Ambroisia Beetle

Ambrosia Beetle

Most ambrosia beetles attack weakened, injured or dying trees and shrubs. Some attack fresh-cut wood as well. A few species attack apparently healthy trees and shrubs. The galleries are excavated by the parent beetles in the sound sapwood, sometimes extending into the heartwood,   and the young stages feed on a fungus growth on the walls of galleries. The young depend on this ambrosia-like fungus for food, which is induced or controlled by the parent beetles.

Beetle tunnels

Beetle tunnels

The beetles excavate tunnels in dead trees in which they cultivate fungal gardens, their sole source of nutrition. After landing on a suitable tree, an ambrosia beetle excavates a tunnel in which it releases spores   of its fungal symbiont. The fungus penetrates the plant’s xylem  tissue, digests it, and concentrates the nutrients on and near the surface of the beetle gallery.

Quercus robur (English Oak)

Quercus robur
(English Oak)

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