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Risk-adjusted strategy for managing tomato insect pest
Following its 2016 incursion into Mpumalanga province, the tomato pinworm Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is now a major threat to successful tomato production in all provinces of South Africa.
AGRICULTURAL RESEARCH COUNCIL
Surveys conducted by Dr Robert Nofemela, a senior researcher at the ARC-Plant Health Protection (ARC-PHP), during 2019 and 2020 in the provinces of Gauteng, KwaZulu-Natal, Limpopo and Mpumalanga, showed that growers are spraying insecticides up to twice a week and up to eight active ingredients in a season in order to suppress the tomato pinworm’s population densities.
While research on other forms of pest control are still at a developmental stage, there is increasing concern about development of widespread insecticide resistance in this pest, and the resurgence of other pests that were under good control prior to T. absoluta invasion.
ARC-PHP recently completed trials in tunnels in Gauteng wherein they investigated: • the potential of using synthetic sex pheromone water-pan traps as a management tool; and • the potential of using the numbers of male moths caught in the traps as a decision tool for when to spray insecticides.
It was determined that utilisation of two traps per tunnel – one at the entrance and the other at the opposite end – is sufficient to suppress the pest infestations on the leaves and fruits, provided moth catches are below 80 moths per trap per week. It is important that the traps always have sufficient water and liquid soap mix to drown the moths. At this low moth catches level, the effect of the pheromone traps is similar to weekly application of an insecticide on the yield obtained.
However, once moth catches exceed 80 moths per trap per week, the efficacy of the pheromone traps diminishes as there is a greater chance of males coming into contact with females and mate before they are caught in the traps. Thus, application of insecticides once moth catches exceed 80 moths per trap per week is recommended. However, it was also determined that once moth catches exceed 200 moths per trap per week, two insecticide applications per week are necessary.
These findings empower growers to use a risk-adjusted strategy for Tuta absoluta management with insecticides. The benefits of such a strategy are optimal insecticide application, reduced input costs and delayed insecticide resistance.
Characteristic damage caused by Tuta absoluta larvae on tomato plant leaves.
