By Grace Kinyanjui
Tuta absoluta is a serious insect pest of tomato. The caterpillars of Tuta absoluta feed on all parts of tomato plant including leaves, flowers, growing shoots and fruits. Damages on tomato fruits cause fruit rot and reduced crop quality. Currently, tomato growers are investing heavily on synthetic insecticides to control Tuta absoluta and other insect pests found on tomato. However, this practice is unsustainable because of increased costs of production and negative impact on human health and the environment.
Can Tuta absoluta be successfully controlled without synthetic insecticides?
Yes. Farmers can effectively control T. absoluta and other insect pests on tomato by adopting an ecologically-based pest management system. This is a holistic approach to reducing dependence on synthetic insecticides and serves as a major component of sustainable agricultural production.
Practices in ecologically-based pest management systems
In ecologically-based pest management systems, a healthy agro-ecosystem forms the first line of defense against T. absoluta attack. Tomato plants require fertile soils and thus, farmers are encouraged to build organically rich soils for better crop nutrition and sustainability. Healthy tomato plants are able to tolerate infestation and damage by T. absoluta. Natural soil fertility can be restored with manure, compost, cover crops and crop residues.
- Adoption of good agricultural practices aimed at preventing or reducing pest infestation.
These include use of clean tomato seeds, proper management of the nursery and transplanting of pest free seedlings. Also, crop rotation of tomato with distantly related crops such as cereals, legumes, leafy vegetables, fodder grasses and onions. Do not rotate with susceptible crops such as potatoes, eggplant, black nightshade or tobacco because they serve as alternative hosts of T. absoluta. A good crop rotation system prevents carry-over and buildup of the pest and also increases soil fertility. Adequate irrigation also prevents water stress, favours optimal growth of the plants and makes them less vulnerable to T. absoluta damage.
Farmers should avoid a monoculture of tomato because it creates a favourable environment for T. absoluta and other tomato pests to thrive. Instead, they are encouraged to embrace polyculture production system. An inclusion of insect repellant intercrops such as basil, garlic and onions can deter T. absoluta from tomato. Flowering plants such as sesame serve as good companion plants of tomato because they provide resources and habitat for the natural enemies.
- Regular monitoring of T. absoluta populations from the nursery stage up to the end of harvesting.
This provides the farmer with information on the onset of the pest attack, the levels of abundance and the effectiveness of any applied control measure. Monitoring can be done using pheromone traps or direct sampling of plants. The pheromone traps are usually loaded with male lures specific for T. absoluta to attract and kill the males. Farmers can also make water traps using basins filled with soapy water and then buy the pheromone lures from companies such as Kenya Biologics Ltd, Dudutech and Koppert Biological Systems. Routine scouting involves visual observation of tomato plants for the presence of adult moths, caterpillars, leaf mines, frass or tiny holes on fruits. High trap counts and visible damage symptoms inform the farmer the need to intervene using an ecologically acceptable approach.
Intervention measures
Possible intervention measures include mass trapping, cultural control, use of biological control agents and application of biopesticides.
- Mass trapping
In mass trapping, the farmer increases the number of traps in the farm to catch a high number of T. absoluta males and reduce the pest pressure. This measure is effective at the early stages of infestation prior to mating and laying of viable eggs by the females.
- Cultural practices
Cultural practices to curb the spread of infestation include the removal and burying of infested plant parts, removal of weeds and wild host plants that can enhance pest’s survival and burying of crop residues after harvest.
- Biological control agents
Biological control agents can suppress the population density of T. absoluta provided the farmers create favorable conditions. These are the natural enemies such as predators, parasitic wasps and insect pathogens. The abundance and species diversity of the existing natural enemies can be increased by diversified cropping systems and reduced use of synthetic pesticides. A foreign parasitic wasp from South America has also been introduced on Kenyan tomato by icipe to help in the fight against T. absoluta.
Commercial and homemade neem-based biopesticides are effective against the pest. Also, biopesticides containing an insect pathogenic bacterium, Bacillus thuringiensis (Bt) such as Baciguard®16WDG (Greenlife Crop protection Africa) can be applied to kill the caterpillars and reduce their damaging impact.
Grace Kinyanjui is a plant pathology expert at Embu University. Email: gracekinyanjui11@gmail.com