South American tomato leaf miner, Tuta absoluta (Meyrick), has been reported in a tomato farm for the first time in Nepal and the presence has been confirmed in five districts, Kathmandu, Lalitpur, Bhaktapur, Kavrepalanchowk and Dhading district. Studies carried out by the Nepal Agricultural Research Council (NARC) in May and June this year have identified and confirmed the presence of the pest in 14 locations in the five districts mentioned above. The highest infestation was identified in two districts, Ugrachandi Nala-2 and Panchakhal of Kavrepalanchowk district.
T. absoluta is an invasive devastating pest of tomato plant originated in South America, Peru, that can infest and damage vast areas of cultivated fields of tomato production as well as other solanaceous crop plants for example, potatoes (Solanum tuberosum L.), eggplant (Solanum melongena L.) and chili peppers (Capsicum annuum L.). Several studies revealed that this pest can infest both protected and open fields and can spread rapidly resulting in significant reduction on the yield and quality of the crop. It is estimated that yield losses caused by the pest can be up to 100% if not controlled adequately and on time. In Europe, North Africa and the Middle East where the pest was introduced, a significant economic damage has been reported.
Typical symptoms of infestation identified in Nepal are dark coloured blotch mines on both sides of the leaves, and leaf folding caused by the larvae of the insect. The damage caused by the pest can occur throughout the entire growing cycle of the crop affecting not only the leaves but also buds, stem and fruit. Heavy infestations result in the death of the whole plant and consequently the entire field.
According to NARC’s distribution map of T. absoluta in Nepal, the pest is spreading very fast from Kathmandu valley into surrounding areas. This pest imposes a serious threat to the sustainability of tomato farmers as this is considered as one of the most demanding regions for tomato in Nepal.
Control of T. absoluta is known to be very difficult as effectiveness of chemical and biological control are limited due to rapid development of resistance to common insecticide and high costs associated with biological control. However, cultural practices such as crop rotation, solarisation, and the elimination of symptomatic leaves and destruction of infested tomato plants can be used to help control this pest.
Furthermore, chemical control using insecticides, usually pyrethrin, carbaryl and deltamethrin has been applied in South America to control the pest since it was discovered but with low to moderate effect due to insecticide resistance of the larvae.
Also, biological control and sex pheromone traps are used to control the pest and as a detection method, respectively. Biocontrol agents for tomato leaf miner are commercially available in North Africa and Europe and have been widely used as a control method.
As the control methods of the pest are limited, information about prevention and detection at early stages is an important way to help farmers reduce the impact caused by tomato leaf miner. CABI in Nepal through the Plantwise program is helping tomato farmers by disseminating information about methods of detection and prevention using different resources, factsheets and social media. Following reports of the new pest within the country, the Plant Protection Directorate, who run the national Plantwise program, conducted discussions and an interactive quiz with the 1,250 members of their ‘Plant Doctors Nepal’ Facebook page: https://www.facebook.com/photo.php?fbid=1563765687253664&set=pcb.1563766453920254&type=3&theater. Cultural and biological methods of controlling the pest can be found on the Plantwise Green List: http://www.plantwise.org/FullTextPDF/2014/20147801309.pdf and further information can be found here: http://www.plantwise.org/knowledgebank/datasheet.aspx?dsid=49260