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HomeFood and Farming ScienceKeep off toxic pesticides from the succulent tomato and the leafy sukuma wiki

Keep off toxic pesticides from the succulent tomato and the leafy sukuma wiki

Most households in Kenya will not go a day without consuming tomatoes and sukuma wiki (kales). The two vegetables, which are popular in Kenya, are also a source of a livelihood to majority of farmers and mama mbogas. Indeed, women provide an estimated 60% of the agriculture labour force across the value chain.

The succulent tomatoes and the greeny leafy sukuma wiki are the major dietary source of the antioxidant lycopene, linked to many health benefits, including reduced risk of heart disease and cancer. They are also a great source of vitamin C, potassium, folate, and vitamin K. Besides this vegetable, considered one of the most nutritious foods per calorie and a superfood, it is also an excellent source of vitamins K, A, C and a source of plant-based calcium. 

However, when we consume these wonder vegetables we are not only taking up nutrients but also toxic chemicals. A recent study, by KOAN and ECOTrac Consulting sampled three markets in Kirinyaga and four markets in Machakos and the verdict was damning – we are consuming toxic laced vegetables. Only one sample out of 19 showed no pesticide levels at all. Some tomatoes showed levels of dimethoate, a pesticide not registered for vegetables and fruits in Kenya. Another 26% of the samples showed high levels of methamidophos, an active ingredient not registered for use in Kenya.

The above tests, which Groen Agro Control Laboratories in the Netherlands did, also highlighted worrying results. Residues of toxic pesticides, which are already withdrawn in Europe, such as carbendazim, acephate, methamidophos and profenofos, were still found in tomatoes and sukuma wiki. The chemicals are withdrawn in Europe based on chronic effects if consumed regularly, they not only could cause cancer (acephate, carbendazim, dimethoate) or certainly mutagenicity (methamidophos, carbendazim) or they show reproduction and development toxicity (carbendazim, dimethoate) or they can cause neurotoxicity (acephate, methamidophos, profenofos). 

This study is not the only one detecting high levels of toxic pesticides. Recent studies by Kenyatta University and Kenya Plant Health Inspectorate Service (KEPHIS) also showed high levels of carbendazim in tomatoes from Kirinyaga and in Nakuru showed high levels of methamidophos. 

Why do we find high residues on tomatoes and sukuma wiki?

Almost 98% of Kenyan farmers suffer from T. absoluta attacks in their tomato fields each season. Smallholder vegetable farmers typically rely on insecticides and spray between 6-10 times per season to manage this pest. As a result, T. absoluta is resisting pesticides, leading to production losses and increased input costs. Recently there has been a blame game going on where the government and the manufacturers of these chemicals have blamed farmers for wrong application of these toxic pesticides. 

However, why blame the farmer when we know there has been complaints of these chemicals not working anymore? A study by Centre for Agriculture and Bioscience International (CABI) in 2019 found out that only 27% of farmers report effectiveness of the current pest control methodology. 

According to CABI, to manage the pest, growers resort to use of broad-spectrum insecticides. However, this practice is unsustainable and likely to lead to widespread development of resistance, contamination of the fruits due to high pesticide residues, and human and environmental health hazards due to overreliance on chemical pesticides. 

Alternatives to pesticide use

Therefore, farmers should be empowered to grow holistically, building healthy soil to grow healthy plants following agroecological principles. Pesticide use should be decreased or even completely avoided. Alternative control methods are available and are proven to control T. absoluta efficiently.

For instance, CABI developed and implemented an Integrated Pest Management (IPM) approach involving the predatory mirid Macrolophus pygmaeus (MIRICAL) and the pheromone trap system (Tutasan and Pherodis). On the other hand, Biovision has developed an approach using the wasp Doligochenidea gelichiidivoris, which controls the leafminer by laying its eggs inside the pest’s caterpillars. The eggs eventually emerge as adult wasps thereby killing the larvae of the pest.

However, not many farmers are aware that natural predators are important and hence protected. Unless we educate our farmers on such alternatives, Kenya might end up like South America whose extensive use of synthetic insecticides led to the development of resistance to all classes of insecticides.

However, not all is gloom and the government should ban pesticides that are most toxic to humans. Such a move will protect Kenyans from these chemicals. The government should also prioritise monitoring and assessment of food residues and resources allocated to protect the long-term health of the population

Besides the above, the government needs to invest in extension services and ensure that there is a shift from an input intensive system of faring to a knowledge intensive agriculture. The two proposed solution if implemented could decrease the costs to the farmer, consumers and protect our environment.

By Silke Bollmohr.

Dr. Silke Bollmohr is a researcher, an ecotoxicologist and a permaculturist can be reached at

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