Majority Of Nyandarua Potato Farmers Misuse Pesticides – Study

Most potato farmers in Nyandarua County are applying pesticides without following recommended safety guidelines, a new study has revealed.

Only 11.85 percent of the farmers adhere to manufacturer instructions, while the rest depend on advice from agrochemical retailers or fellow farmers.

The revelations were made on Thursday during a session between the Senate Agriculture, Livestock and Fisheries Committee and researchers from Egerton University. The committee, chaired by Bungoma Senator Wafula Wakoli, convened to examine the extent and impact of pesticide misuse in Kenya’s potato sector.

Researchers Prof. Joseph Wafula Matofari, Dr. John Masani Nduko, and Millicent Kanario presented findings from their study titled “Influence of On-farm Pesticide Practices and Processing Methods on Pesticide Residue Levels in Potato Tubers”. The research was conducted in Nyandarua, Kenya’s top potato-growing county.

According to the study, 98.8 percent of smallholder farmers in the region use synthetic pesticides. However, many are unaware of proper application practices. The study found that farmers often mix various pesticide products—including fungicides, insecticides, and foliar fertilizers—and apply them frequently, in some cases on a weekly basis.

“This misuse has led to excessive pesticide residues in potato tubers,” said Prof. Matofari. He noted that traces of banned insecticides such as chlorpyrifos and fenitrothion were detected in the samples. These chemicals were found at levels above the maximum residue limits set by the European Union and Codex Alimentarius.

The research further linked high pesticide residue levels to early harvesting. Potatoes harvested just three weeks after spraying contained significantly higher chemical concentrations.

The study also assessed how household cooking methods affect residue levels. While boiling, frying, and steaming reduced most pesticide traces, some chemicals—especially chlorpyrifos—remained above international safety limits even after cooking.

The committee raised concerns over the findings and pointed to several underlying issues, including poor farmer training, limited access to agricultural extension services, and weak regulatory oversight.

Senator Wakoli called for urgent action to improve monitoring by the Pest Control Products Board and to boost public awareness on the safe use of pesticides in food production.