Invasives Blog

Tomato is one of the most important vegetables grown in Kenya and plays a critical role in income generation and creation of employment for both rural and urban populations, in addition to meeting food nutritional requirements.

Tuta absoluta – also known as tomato leafminer – is a native of South America (Peru) and is one of the most economically damaging tomato pests wherever it has invaded. It has become invasive in introduced ranges having escaped the biotic constraints, which keep their populations in check in their regions of origin. Infestation by this pest has the ability to cause yield losses of up to 100%.

Since it was first reported in Kenya in 2014, T. absoluta has become a serious threat to the sustainable production of tomato in Kenya with nearly 98% of tomato farmers affected. For a long time, chemical control (use of synthetic pesticides in pest management) has been the go-to option in the management of Tuta absoluta. This control strategy has several negative effects on the environment, natural enemies and other beneficial insects, human and livestock health, and largely, it has increased the cost of production by up to 10-fold. In Kenya, nearly 96% of farmers apply chemical pesticides to manage Tuta but only 27% report effectiveness. Different approaches and strategies have been developed and validated through trials in the open field and green houses for the management of T. absoluta.

Like other major exotic pests Tuta is/has adapted for wide dispersal and high rates of reproduction, becoming established with increasing frequencies on all continents and on many ecologically sensitive islands. Area wide pest management (AWPM) therefore provides an alternative and sustainable approach that can be used for the management of insect invaders.

Areawide pest management is defined as the “long-term planned campaign against a pest insect population in a relatively large predefined area with the objective of reducing the insect population to a non-economic status”. The concept of AWPM is to address the whole pest population including all places of refuge or foci of infestation from which recruits could come to re-establish damaging densities of the pest population in areas of concern.

A key feature of AWPM is that it is a long-term campaign over a large geographical area, and not a one season activity. It provides a more cost-effective and sustainable approach by proactively targeting entire pest populations. In this way, pest populations can be contained at low levels for longer periods and pest management methods can be integrated that are less reliant on synthetic pesticides and that better address ecological and environmental concerns.

Although some of the methods deployed in AWPM may be costly and in some instances may not be affordable by individual farmers, when this strategy is deployed by a community, the per capita investment is lower compared to other conventional methods, and benefits accrue to all.

Currently, the control of many highly mobile and very destructive insect pests is still carried out, for the most part, by individual producers who rely heavily on the use of insecticides. Although other control technologies are often incorporated into the producer’s integrated pest management (IPM) system, these technologies, too, are usually applied by producers independently of other producers, and without due consideration of surrounding host and non-host areas. Such uncoordinated farm-by-farm efforts often prove inefficient since they only suppress a proportion of the targeted pest population. Pests from nearby untreated areas remain unscathed and can re-enter the treated areas, the damage continues, and people have little choice but to apply the control measures again and again to protect their livelihoods.

CABI and Koppert Kenya with funding from the Netherlands Ministry of Agriculture, Nature and Food Quality (MinLNV) under the project, “Demonstrating biological approaches for sustainable management of tomato leaf miner in Kenya,” have joined forces to provide and demonstrate alternative biological approaches for sustainable management of tomato leaf miner. The project aims at working with small-holder tomato growers in the outskirts of Nairobi and Kajiado Counties, to try out innovative biological control approaches for the management of the tomato leaf miner, Tuta absoluta, experience the benefits, and provide lessons and evidence for furthering the uptake of reduced risk pest control products in Kenya.

To understand methods and approaches farmers are using to manage leaf miner, a cost benefit baseline study was conducted in November-December 2019. One of the areas of focus was finding out whether tomato farmers were aware of AWPM and if there were any community-based efforts/services for ensuring area-wide management of pests.

Although only a small number (9%) of farmers reported of be aware of AWPM concepts, the examples they gave were indeed a true reflection of AWPM practiced at community level. The farmers described synchronized pest management – scheduled spraying by communities, planting at the same time to ensure that crops are the same age, and jointly destroying the breeding areas.

But 4% reported to know of some activities related to AWPM in the study areas. Farmers at Isinya, Kajiado reported that T. absoluta is a mobile pest, hopping from one farm to another and since as a community they had not reached a situation where they synchronise planting, spraying same days while some farmers do not spray at all, leaf miner has remained a threat, resulting in their farms being re-infestedeven after spraying. To address this problem, the farmers said that during the growing season they spray their neighbours farm edges to ensure that pests do not migrate directly to their farms.

The institutionalization of AWPM would be a great milestone in ensuring buy-in among all stakeholders. Although not a new concept, AWPM has not been widely used in the management of the invasive pests like T. absoluta. To ensure complete institutionalization, there should be a structured approach in rolling out the technology where all stakeholders are brought on board. In the cost benefit analysis study, the team also sought to find out from the farmers how easy or not is it to institute the AWPM concepts and most farmers (59%) were emphatic that it is very possible.

Tuta absoluta damage

One farmer from Isinya, Kajiado said: “This is a very good concept. With the bioproducts, it can help farmers a great deal in dealing with the leaf miner menace. Effective control of the pest has not yet been attained because the pest easily migrates from neighbours’ farms.”

“Last season, I lost 12 acres of tomato to the pest and I am contemplating giving up tomato farming. But by working with neighbours, we can make sure it doesn’t migrate again from their farm to mine.” he continued.

Nevertheless, the majority of farmers (61%) believe that area wide pest management can work in the control of invasive pests and suggested that what needs to be done is increased awareness of the concept among farmers, community sensitization, making the right technology available to farmers at the right time, training of both the extension staff and lead farmers, and farmers agreeing to plant at the same time and scheduling application of control measures at the same time. By so doing, this will guarantee successful implementation of the AWPM concepts and would save farmers from the huge losses they incur every season as a result of pest infestation and failure of the applied chemicals to effectively control the pests.

Find out more

Project page: Demonstrating biological approaches for sustainable management of tomato leafminer in Kenya

Invasive Species Compendium: Tomato leafminer portal

CABI Evidence Note: Tomato leafminer (Tuta absoluta): impacts and coping strategies for Africa

Tomato farmers in Kenya willing to use integrated pest management and bioproducts to manage Tuta absoluta

How can tomato farming be improved in Kenya? Study finds producers face a ‘myriad of constraints’

All images ©CABI

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