TRB warns farmers of new destructive pest

©Hywit Dimyadi via 123RF

In an alert, TRB said Tuta absoluta, originating from South America recently invaded Zimbabwe and current reports indicate high levels of damage in tomato. The tomato is the preferred host of the pest, both in its native and invaded territories.

The pest is fast spreading in Zimbabwe and has already caused heavy losses in tomato. However, in the absence of the primary host, Tuta absoluta is known to attack closely related crops such as tobacco, potato, pepper, eggplant and solanaceous weeds. In extreme cases it has been reported on cabbage, kales and other vegetables of the Brassica family. Furthermore, TRB said what makes the pest a real but silent threat, is its close resemblance to the ordinary leafminer currently known in the tobacco agrosystem. The adult moth lays eggs on the tomato plant leaves, stems or fruit. When eggs hatch, larvae burrow into the leaf lamina causing loss of photosynthetic area thus resulting in large blister like portions of merged tunnels or mines.

The larvae also gnaw away stems and leaf stalks and burrow into fruits causing extensive rotting.

"Tuta absoluta has a high propensity of developing resistance to various insecticides that are known to effectively control other leafminers. Currently in Zimbabwe, no tests have been conducted to establish effective insecticides that can be used to control the pest," the board said. Growers who have already encountered this pest on tomato are encouraged to exercise extreme restraint and caution in using insecticides. There are incidences in Bindura where Tuta absoluta populations are already showing increased tolerance to insecticides as a result of uncoordinated control programmes involving spraying various pesticides that have not been tested.

In other parts of the world, growers have managed to delay the onset of insecticide resistance by using a combination of specific pesticides with different modes of action, pheromone traps, biological control and cultural practices.

"We encourage farmers to scout their fields regularly, paying great attention to the lower leaves of the crop. Where leaves show symptoms of mining, one has to gently prod the mined portion to expose the burrowing larvae. A clear examination of the maggot head will give a quick indication of the identity of the infesting leafminer," the board said.

"Whenever Tuta absoluta infestation is suspected, growers must get in touch with the Tobacco Research Board or bring infested samples to our plant clinic immediately."

Always remember that correct identification of the pest is important before deploying any control measure. In addition, after implementing a particular control tactic, ensure adequate monitoring to establish effectiveness of control measure and revise strategies if necessary. The TRB is currently working closely with stakeholders to ensure timeous intervention should the pest be reported on tobacco.