Zim gum trees threatened


The alien insect, believed to have originated from Australia, is causing three types of diseases that are threatening the national gum tree hectarage.

Kenneth Matimaire
MUTARE — Zimbabwe’s vast eucalyptus (gum tree) plantations are under attack from an exotic insect that is causing diseases to the tree species.
The alien insect, believed to have originated from Australia, is causing three types of diseases that are threatening the national gum tree hectarage.
These are leptocybe invasa (blue gum calcid), thaumastocoris peregrinus (bronze bug) and glycaspis brimblecombei (red lerp psyllid).
Leptocide invasa has been cited as the most deadly disease because the insect enters and lays eggs in the stem of a gum tree at the nursery stage, leading to the formation of gulves, which reduce the tree’s growth.
Normally, at three months, eucalyptus nurseries are supposed to be more than 30 centimetres in height but are currently reaching 90 days still far below the expected height.
Apart from stunting growth, the disease causes multiple shoots and meandering of the stem, thereby making the mature tree unsuitable for timber production.
“We have a challenge. Our challenge is affecting our nurseries. It is called blue gum calcid. If you look at our nurseries, they are not appealing. Some of the leaves are tiny…But because of the blue gum, they no longer grow, so it’s a national disaster,” said Hardly Taziwa-Mutasa, a district field officer with SaFIRE, which is part of the Forest Forces, an organisation fighting to protect sustainable environmental programmes.
The advent of gum tree diseases has partly affected the national timber hectarage, which dwindled from a total 108 214 hectares to 80 000 hectares in the past decade, with eucalyptus plantations recording the major decrease, according to statistics from the Timber Producers Federation.
The Food and Agriculture Organisation, in conjunction with government through the Forestry Commission, in 2012 launched a pilot project on reducing the impact of the alien invasive species.
The project aims at establishing mitigation measures against the diseases.
These have been conducted in Manicaland (Mutasa District), Mashonaland East (Marondera and Wedza), Midlands (Shurugwi and Lower Gweru), Mashonaland Central (Shamva district) and Mashonaland West (Chegutu district).
“We have tried something to mitigate this problem. We have introduced a biological control that was imported from Australia. It is called neseri. It is used in Australia to fight the blue gum calcid.
“So, we conducted a research to verify whether this biological control will have the same results as those recorded in Australia (or not) because there were fears that it might respond to other tree species here. But we are glad to indicate that it has been successful and is responding positively. It has managed to fight the blue gum calcid in the nurseries. We conducted the pilot project here in Mutasa,” said Forestry Commission’s Mutasa district officer, Tanner Magedo.
“We immediately approved the findings of our research after the very same biological control was approved in South Africa, which was facing a similar problem.
“Implementation started in September as we proceeded to establish nurseries,” Magedo added.

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