The devastating tomato leaf miner, Tuta absoluta, poses significant challenges to South African farmers, particularly in the regions of Limpopo, Gauteng, and Mpumalanga. Since its detection in the country in late 2016, this invasive insect from South America has caused considerable crop damage, leaving farmers scrambling for solutions.
Blessing Mphahlele, an entomologist and PhD candidate at the University of Pretoria, provides research-based tips to effectively manage the tomato leaf miner while promoting sustainable farming practices.
Understanding the threat
The tomato leaf miner feeds primarily on tomatoes but can also infest other Solanaceae crops like eggplants, peppers, and potatoes. Its ability to thrive on wild host plants in the absence of these crops complicates management efforts.
According to Mphahlele, the tomato leaf miner can lead to up to 100% crop yield loss without effective strategies. This economic impact demands collaboration between farmers and researchers to implement integrated pest management (IPM) strategies. IPM emphasises using multiple complementary pest control measures instead of relying solely on chemical insecticides.
“It is impossible to completely eradicate pest populations from the environment. Therefore, we aim to maintain pest populations at acceptable levels by using various control measures in combination,” Mphahlele says.
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Pitfalls of insecticide dependency
While insecticides are a common control method, Mphahlele warns that the tomato leaf miner has a high potential to develop insecticide resistance. Over-reliance on insecticides can render these chemicals ineffective, forcing farmers to confront the tomato leaf miner without viable alternatives.
“Farmers are using chemical control as the primary method, but we need to discourage this,” Mphahlele explains. “Insecticide application should be a last resort after other control measures have been tried.”
3 practical IPM strategies for farmers
Pheromone traps for monitoring
Pheromone traps are a vital tool in assessing populations of the leaf miner. Mphahlele’s research suggests using a threshold of 50 moths per trap before considering insecticide application. Experiments in Gauteng showed that farmers who waited until this threshold was reached used fewer insecticide applications without increased crop damage.
“Farmer A, who sprays weekly, and Farmer B, who waits for 50 moths per trap inside tunnels, see similar crop damage,” Mphahlele explains. “However, Farmer B incurs lower operational costs and reduces the risk to beneficial insects and human health.”
Biological control with natural enemies
Researchers have identified Nesidiocoris tenuis, commonly known as the nesibug, as a natural predator of the tomato leaf miner.
“During Covid, Agricultural Research Council (ARC) researchers found the nesibug in tomato-producing areas,” Mphahlele notes. “But unfortunately, farmers inadvertently kill these beneficial insects with conventional insecticides.”
Protecting and fostering these natural enemies is crucial for effective biological control against the tomato leaf miner.
Combining control methods for maximum impact
Mphahlele stresses that biological and chemical control methods should not be viewed as alternatives but rather used together.
“IPM encourages combining control methods to enhance their effectiveness. This holistic approach safeguards the environment and promotes human health,” Mphahlele says.
- Mechanical control: Regularly remove and destroy infested leaves to reduce populations of the tomato leaf miner.
- Cultural control: Rotate crops and implement intercropping strategies to disrupt the breeding cycles of the tomato leaf miner.
To create a sustainable and effective pest management system, Mphahlele recommends that farmers balance chemical, biological, and mechanical methods.
“Farmers should adopt an IPM approach that combines these methods,” he says. “This strategy strengthens each method’s effectiveness and supports a healthier environment.”
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