Farmers in Africa are putting consumers at risk by using unlicensed pesticides to fight leaf miner (Tuta absoluta) in tomatoes.

“Excessive residues in tomatoes may lead to chronic diseases such as cancer, as well as contribute to the development of neurodegenerative diseases such as Parkinson’s and Alzheimer’s diseases,” warned scientists from the International Centre of Insect Physiology and Ecology (Icipe) at the launch of safer management of the pest in parts of Kenya.

The scientists say they are also worried about the abundance and ease of access to internationally banned pesticide sprays, which pose serious health risks to tomato farmers, consumers and the environment.

Scientists involved in different studies on the leaf miner pest warned of the long-term health effects of pesticide use in Africa. Most farmers spray the pesticide directly on ripening tomatoes and don’t observe pre-harvest intervals.

According to scientists from Centre for Agriculture and Bioscience International-CABI, a human health risk assessment done in Ghana showed high cancer risk for adults and children due to the presence of chlorpyrifos, an organophosphate pesticide.

The study by CABI in Kenya and Zambia identified six active ingredients in use in both countries, which are considered highly toxic (WHO Class 1b) and some are banned or restricted.

“Farmers in Kenya were found to be using Beta-cyfluthrin while those in Zambia are using Monocrotophos. This is a major concern because in countries where such products are still used application is only recommended for non-food products,” said Ivan Rwomushana, senior scientist, Invasive Species Management.

“Farmers are using these products on tomato illegally. The use of such products on cultivated foods, such as tomato, should be discouraged,” said the team in a technical paper, adding, “There is a need to assess the current situation in African countries where high pesticide use against this pest is prevalent.”

Another concern is that farmers use the pesticides without adhering to the appropriate safety precautions. At least 34.8 percent of farmers in Kenya and 38.3 percent in Zambia did not use any personal protective equipment, according to the CABI survey.

About 30.6 percent of the farmers surveyed in Kenya and 24.8 percent in Zambia reported itching of the skin, which is a frequent side effect, after using the chemicals, while nearly 31.5 percent of farmers in Zambia reported headaches. Other side effects included stomach ache and dizziness.

Now, scientists are urging for the use of integrated pest management (IPM) practises to deal with tomato leaf miner, also called pinworm. These IPM practises will reduce damage caused by pesticides, increase yield and quality of tomatoes, protect the environment and safeguard human health — through reduced use of synthetic chemicals. Farmers in Africa currently depend on synthetic chemicals for the control of the pest.

“Once tomato fruits are formed, it is advisable to eliminate pesticide usage at all costs,” said Shepard Ndlela, Icipe’s co-ordinator of the Tuta Absoluta control project, adding, “Only green label-soft insecticides should be applied when absolutely necessary.”

The leaf miner (a pest that develops into a moth), is most destructive at the larvae or caterpillar stage, and has gained notoriety as the most devastating tomato pest in Africa. First reported in Chile, the pest spread to other regions between the 1960s and 1980s. It was first recorded outside neo-tropical America in Spain in 2006, from where it spread to other countries, including sub-Saharan Africa, first in North Africa — Tunisia and Morocco — in 2008.

The pest is reported in 41 of Africa’s 54 countries. In East Africa, the pest was first reported in Kenya and Tanzania in 2014, then Rwanda and Uganda in 2015 and 2016 respectively. It is now a serious threat to the sustainable production of tomatoes in the region with some farmers reporting 100 per cent loss of their crop.

In Ethiopia, the yield loss due to the pest was reported by one study to be in the range of 60.08 to 82.31 percent while in Sudan, it was between 80 to 100 percent. In Zambia, about 90 percent of crop damage has been reported while in Tanzania, the mean plant damage inflicted by the pest in all tomato fields was reported to be between 90 and 100 percent.

It is estimated that Africa produces 37.8 million tonnes of tomatoes annually. But the study in 2018 showed that between 99 percent and 97.9 percent of farmers reported pinworms as a problem in their tomato fields in Kenya and Zambia, respectively.

The mean seasonal production loss due to the pest, based on farmers’ own estimates, was at least 114,000 tonnes for Kenya and 10,700 tonnes for Zambia. This translates into $59.3 million, and $8.7 million in economic losses for Kenya and Zambia, respectively.

Beyond the increase in synthetic insecticide applications, the impact of infestation has included increasing tomato prices due to the cost of crop protection, bans on the trade of tomato including seedlings, and seasonal scarcity around the continent.

Use of synthetic pesticides has been the go-to option in the management of pinworms, increasing the cost of production as much as tenfold.