Called gum trees because they exude copious amounts of gum from any break in the bark….
Gum trees are very much a part of our history in South Africa. The mighty giants deserve admiration and the individual non-invasive trees need to be protected. There is something quite beautiful that happens when that late afternoon light falls on the gum tree trunk. The bark of the tall unbranched saligna gum peels away in papery slices to reveal a powdery bluish white under bark which is so stunning that its beauty can literally take your breath away. The bark of many Eucalypts is smooth and shed annually, resulting in new and old bark making a colourful contrast while this is happening. The eucalyptus smell after it has rained is unforgettable, and the dark red-brown little ‘pellet’ shaped fruit capsules that dug into the soles of your bare feet as a child cannot but remind you of your childhood days running barefoot all day long. In my mind a farmhouse is not a farmhouse without a cluster of shade-giving gums alongside it. They were planted to act as windbreaks in otherwise quite hostile parts of the country primarily because they grow so fast.
Approximately 300 species of Eucalypts in this diverse genus of over 600 or so known species of evergreen trees of the myrtle family, were originally introduced into Southern Africa from Australia. So, love them or loathe them they have provided South Africa with a huge forestry industry. They were introduced primarily for the usage of timber in construction, as mine props and firewood and in time was used in the newly established paper industry. The bee-industry is largely dependent upon blue gum trees for the good honey from the floral nectar the gum trees provide. The leaves contain aromatic oil in small translucent cavities hence that very strong aroma you get after crushing or standing on the leaves. Eucalypts were first brought to Europe by Captain Cook’s Australian expedition.
Almost 18 months ago a very serious disease infected the gum trees in our region. They are full of galls and, in some cases, like our gums on the Greater Woodmead Estate are covered with the white lerps of Glycaspis brimblecombei. This little insect is native to Australia and was first detected in South Africa in 2012. The insects feed by inserting their mouth, a sucking straw, into the leaf and sucking out the liquids. This sugary liquid passes through their system, and is excreted as a sticky substance called honeydew. This honeydew forms a crystalline shell or lerp over the bug, leaving the leaves literally covered all over with these lerps. This sticky honeydew on the leaves results in blackened foliage due to the growth of sooty mould.
If you glance up into the gum trees on the golf course white spots literally cover every inch of the leaves. Try scratching off one of these lerps and you will find a tiny, wingless insect underneath. The high infestations of these insects has resulted in severe die-back, defoliation, bark splitting and general blackening of the trunks. The overall condition of the gums trees is alarming and unsightly. Fortunately a replacement planting program has been in place for at least 2 years and these new trees are doing well.
Research is presently underway on a potential biocontrol agent of this lerp, primarily to test whether it will be safe for release in South Africa and without attacking native insects. Entomologists at the Forestry and Agricultural Biotechnology Institute (FABI) at the University of Pretoria have been hard at work in northern Limpopo collecting the native mopane lerp for host specificity testing.
The good news is (hot off the press) that Entomologists at FABI have recently discovered in the Pretoria area, a natural enemy, the parasitic wasp Psyllaephagus bliteus, of the red gum psyllid. This parasitic wasp is essentially the same insect currently undergoing host specificity tests, but now that it exists here naturally the time taken to spread it across the country will be much shorter. In fact, it may already be present in certain areas, but this still needs to be determined. This wasp is also native to Australia and has been intentionally introduced to other countries as a biological control agent for the red gum lerp psyllid. It is unclear how it arrived in South Africa, but most likely on the same pathway that resulted in the introduction of the psyllid. Can you believe this little predator is small enough to sit on the head of a pin! Hopefully the introduction of these parasitic wasps will stop the widespread destruction of these trees, allowing some trees to recover.
There is no doubt that, the popular view is that the gum tree with its water-sucking capabilities is causing the drying up of springs, healthy rivers and water sources generally and there is some truth in this. Together with global climate change and the prediction that water will become scarcer, environmental groups predict a growing crisis for much of South Africa if water hungry alien exotic trees continue to be allowed to propagate to the detriment of local plants and indigenous species. It is believed that an average sized gum can take up to 200 litres of water per day!
South Africa’s current environmental regulations emphasize the conservation of water and the protection of our indigenous flora. There can be no doubt that the blue gum is not everyone’s favourite, but when first introduced to South Africa around the 1870’s the Eucalyptus gum was a species prized for its strong wood, its aesthetic beauty, its ability to grow quickly in warm and arid areas, where other trees could not, and ironically also for its water-sucking capability which could drain marshy areas which helped in eliminating malaria, a very real problem in Africa at that time.