Estimated reading time: 5 minutes
The potato industry in South Africa plays a vital role in agriculture and food security, contributing significantly to both local consumption and export markets. However, potato cultivation is constantly threatened by various pests and diseases. Among these, the potato leaf miner, Liriomyza huidobrensis, will be the focus of this article.
The potato leaf miner, belonging to the insect order Diptera and the family Agromyzidae, is originally native to South America. It has since spread to various parts of the world, including Africa, Asia, and Europe. This insect is known for its ability to damage a wide range of crops, but its primary target in South Africa is potatoes, which constitute an important food crop.
The adult potato leaf miner is a small fly that lays its eggs on the leaves of the potato plant. Upon hatching, the larvae burrow into the leaf tissue, feeding between the upper and lower surfaces of the leaves, creating visible mines. These mines reduce the plant’s ability to photosynthesise, stunting growth and leading to poor crop yields. In severe infestations, the damage can be so extensive that it leads to the death of the plant, severely affecting the harvest.
Biology and life cycle
The potato leaf miner has a complex life cycle, making it a persistent and adaptable pest. The insect undergoes four stages: egg, larva, pupa, and adult.
- Egg stage: Female flies lay their eggs on the surface of potato leaves, usually along the veins. The eggs hatch after three to seven days, depending on environmental conditions such as temperature and humidity.
- Larval stage: The larvae are the damaging stage of the pest. Upon hatching, they burrow into the leaf tissue, feeding between the upper and lower surfaces. This feeding creates characteristic blotchy mines in the leaves. These mines disrupt the plant’s ability to photosynthesise, weakening the plant over time.
- Pupal stage: After feeding, the larvae drop to the soil, where they pupate in the ground. The pupation period lasts for ten to 14 days, and the insect can overwinter in this stage, particularly in cooler climates.
- Adult stage: The adult fly emerges from the pupa, ready to mate and start the cycle over again. Adults are small, with a characteristic black and yellow striped body. They can fly long distances, allowing them to spread rapidly from one field to another.
Impact on potato crops
Having entered the country in 2000, the potato leaf miner has been a serious issue for potato producers in the Sandveld region, initially resulting in severe losses of up to 70% and spreading to other potato-producing regions thereafter.
South Africa is one of the leading potato producers in Africa, with major growing regions in the Western Cape, Limpopo, and the Free State. Potatoes are not only crucial to the local economy but also form an important part of the diet of many South Africans.
Potato leaf miners damage the leaves of potato plants, which reduces the plant’s ability to conduct photosynthesis effectively. This leads to stunted growth and lower yields. In severe cases, entire crops may fail, especially if the pest is not timeously controlled. The presence of leaf miner larvae on leaves affects the overall health of the plant. Even if the plant survives, the damage can lead to a reduction in tuber quality.
Mined leaves may cause stress to the plant, resulting in smaller and fewer potatoes. Moreover, the pest can also increase the vulnerability of the plant to other secondary infections, such as fungal diseases.
The economic costs of potato leaf miner infestations will be significant if not taken seriously. Producers face both direct costs from yield losses and indirect costs from the control measures required. Additionally, the reduced quality of the potatoes can negatively affect their marketability, leading to financial losses.
Read more about the Potato tuber moth.
Management
In terms of cultural control, practices such as crop rotation, sanitation, maintaining good crop health and considering less susceptible cultivars (i.e., cultivars with a naturally darker green hue) can aid in managing infestations.
Early detection and regular monitoring of potato fields are key to preventing large-scale infestations.
Producers may employ yellow sticky or water-filled pan traps to monitor leaf miner activity. The earlier the pest is detected, the more manageable the infestation becomes, reducing the need for heavy pesticide use.
More often than not, insecticides will be relied upon to manage potato leaf miner infestations. Most registered product formulations on the local market are systemic or have a translaminar effect. While contact insecticides may be an effective means of controlling flies, they are ineffective in controlling the larvae (pest destructive stage), which remain protected by the dead epidermis of the mines.
For effective insecticide control:
- Do not allow a population to be established.
- Fields should be monitored daily and spraying operations should commence at the first signs of leaf miner.
- Ensure thorough coverage of every leaf.
- Spray using the correct spray equipment, spray heads, additives and at the right time of day.
- Consult your crop adviser or pest management consultant when unsure.
When it comes to using pesticides in general, producers must remember that the label of a pesticide product is a legal document under the Fertilizers, Farm Feeds, Seeds and Remedies Act, 1947 (Act 36 of 1947). Ensure products are registered for their intended purpose. Further, store, handle, and apply pesticides without any deviation from the label instructions whatsoever.
Any employee handling or spraying pesticides must be provided with the necessary protective clothing and equipment. Finally, be sure to dispose of all empty containers with a CropLife SA-certified recycler in your area.
Containers must be triple-rinsed according to the CropLife SA cleaning guidelines otherwise they will not be accepted. All certified recyclers and their contact details are listed on the CropLife SA website: www.croplife.co.za/Home/CertifiedRecyclers. In this regard, also take note of the disposal statement on labels. For more information regarding container management, visit the CropLife SA website: www.croplife.co.za/Home/ContainerManagement.
Conclusion
The potato leaf miner poses a significant threat to potato production in South Africa. The economic impact on both local and export markets underscores the need for integrated pest management approaches, by combining all available measures to mitigate the damage caused by this pest. As the potato leaf miner continues to challenge South Africa’s potato industry, ongoing research and adaptation of pest management strategies will be essential to safeguard this vital agricultural sector. – Hiresh Ramanand, stewardship specialist, CropLife SA
For more information, email the author at hiresh@croplife.co.za.