Potatoes grown in Nyandarua County have raised eyebrows following a study by Egerton University researchers, who say unsafe pesticide practices are contaminating the crop and potentially endangering consumers.
The research, led by Egerton University’s Department of Dairy and Food Science and Technology, reveals that nearly 99% of farmers in the region use synthetic pesticides, with a high number of the growers disregarding manufacturer guidelines and safety recommendations.
The study detected multiple residues of pesticides in raw potato samples, including instances where chemical residue levels exceeded European Union (EU) and Codex maximum residue limits (MRLs).
The study also showed significant deviations from recommended pesticide use.
Why Nyandarua Potatoes Are Unsafe
Common active ingredients include mancozeb, metalaxyl, and cymoxanil in fungicides; α-cypermethrin, imidacloprid, and λ-cyhalothrin in insecticides; and glyphosate, 2,4-D, and atrazine in herbicides.
Only 12% of farmers follow manufacturers’ dosage guidelines, while 74.8% rely on agrochemical retailers and 13.2% on other farmers for advice.
“Potato tubers from farmers who adhered to manufacturer instructions for pesticide application had significantly lower residue levels,” the study noted, with no detectable residues of 2,4-D, atrazine, or metolachlor and lower glyphosate levels (0.44 μg/kg) compared to 4.63 μg/kg from agro-vet advice.
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Additionally, the researchers note that 60.8% of farmers spraying weekly, often regardless of pest or disease presence.
Harvest and Processing Methods
On the other hand, 36.8% of farmers harvest just three weeks after spraying, resulting in elevated residues compared to a five-to-six-week preharvest interval.
Processing methods like frying and boiling significantly reduced residues, with frying cutting azoxystrobin by 92.4% and boiling reducing metalaxyl by 91.3%.
However, fenitrothion and chlorpyrifos remained above safe limits even after frying, baking, or roasting.
“There is widespread noncompliance among potato farmers in Nyandarua County regarding manufacturer instructions,” the researchers concluded, urging expanded initiatives to promote good agricultural practices.
Potato value chain employs 2.5–3 million people, including farmers, traders, processors, and transporters. Potatoes are Kenya’s second-most important staple crop after maize.
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With demand outpacing supply, pressure is mounting on farmers to maximize yield, often at the expense of safety.
Potato Business in Nyandarua
Nyandarua County is Kenya’s leading potato-producing region, contributing 30–35% of the nation’s total potato yield.
Potatoes (Solanum tuberosum) are Kenya’s second-most important staple crop after maize, playing a critical role in food security and economic development.
Nyandarua produces approximately 550,000 tonnes of potatoes annually on 37,000 hectares, with an estimated market value of Ksh9 billion.
In 2023, the national potato sector was valued at Ksh74 billion, with Nyandarua’s contribution likely higher than earlier estimates due to inflation and increased production.
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