Assessment of organophosphate insecticide application practices among smallholder tomato growers in central Kenya

Introduction

Tomato (Solanum lycopersicum L.) ranks among the most economically significant vegetable crops in Kenya, providing livelihoods to thousands of smallholder farming households across the country. The crop is cultivated extensively in central Kenya, where favorable agro-climatic conditions support year-round production. However, tomato cultivation is constrained by several biotic stresses, including infestations by aphids (Aphis gossypii Glover), whiteflies (Bemisia tabaci Gennadius), tomato leafminers (Tuta absoluta Meyrick), and various Lepidopteran pests that substantially reduce yields if left unmanaged. In response to these pest pressures, smallholder farmers have become increasingly reliant on synthetic chemical insecticides as their primary pest management strategy. Among the various insecticide classes available, organophosphates have historically dominated the market in East Africa due to their broad-spectrum activity, relatively low cost, and widespread availability through local agrochemical supply chains. Products containing chlorpyrifos, dimethoate, and profenofos are routinely stocked by agrochemical dealers in rural townships and trading centers throughout central Kenya. Despite the extensive use of organophosphate insecticides in smallholder tomato production systems, several concerns have emerged regarding their application practices. Previous investigations in neighboring countries have documented widespread misuse of pesticides, including over-application, inadequate protective equipment usage, improper storage, and failure to observe pre-harvest intervals. These practices not only compromise the health of farming communities but also contribute to environmental contamination and the development of pesticide resistance in target pest populations. The information sources that farmers rely upon for pest management decisions represent another critical dimension of insecticide usage patterns. While government extension services are designed to provide science-based recommendations, the limited reach of extension officers in rural areas has created an information vacuum that is often filled by commercial agrochemical dealers whose advice may be influenced by profit motives rather than technical appropriateness. Understanding the specific insecticide application patterns at the local level is essential for designing evidence-based interventions that can improve pest management outcomes while minimizing health and environmental risks. Although several broad-scale surveys have examined pesticide use in East Africa, localized investigations focusing specifically on organophosphate usage patterns among tomato growers in central Kenya remain scarce. This research was therefore undertaken with the following objectives: (1) to characterize the insecticide usage patterns among smallholder tomato growers, (2) to evaluate the extent of personal protective equipment usage during insecticide application, (3) to identify the primary information sources influencing insecticide selection decisions, and (4) to examine the relationship between farming experiences and spray frequency. The role of agrochemical dealers in shaping farmer decision-making regarding insecticide selection has gained increasing attention in the agricultural extension literature. In many sub-Saharan African countries, agrochemical dealers serve as the de facto primary source of pest management advice for smallholder farmers, often surpassing government extension services in terms of accessibility and frequency of contact. This reliance on commercial sources for technical guidance raises important questions about the quality and objectivity of the information transmitted to farmers, particularly regarding appropriate application rates, pre-harvest intervals, and the selection of insecticide classes suited to specific pest-crop combinations. The extent to which dealer-driven information dissemination influences organophosphate usage patterns among Kenyan tomato growers has not been systematically investigated, and this gap in the evidence base constrains the ability of policymakers to design effective interventions that promote safer and more efficient insecticide use practices.

Material and Methods

Material

The research was carried out in three sub-counties of Kiambu County in central Kenya, namely Gatundu South, Thika Town, and Ruiru, during the period from March 2025 to February 2026. These locations were purposively selected based on their prominence in smallholder tomato production and the documented high levels of insecticide use among farmers in the region. The study area lies between latitudes 1.0°S and 1.2°S and longitudes 36.8°E and 37.1°E, at elevations ranging from 1,400 to 1,700 meters above sea level.

Methods

A cross-sectional survey design was adopted for this research. A total of 240 smallholder tomato farmers were selected using a multi-stage sampling procedure. In the first stage, three sub-counties were purposively selected. In the second stage, four wards were randomly selected from each sub-county. Finally, 20 farmers were randomly selected from each ward using farmer registration lists maintained by local agricultural offices. Data were collected using a pre-tested structured questionnaire administered through face-to-face interviews. The questionnaire captured information on sociodemographic characteristics, insecticide types and brands used, application frequency and dosage, personal protective equipment usage, sources of pest management information, and pesticide handling practices. Additionally, direct field observations were conducted on 60 randomly selected farms to validate the self-reported data. The collected data were coded and entered into IBM SPSS Statistics version 28 for analysis. Descriptive statistics including frequencies, percentages, and means were computed for all categorical and continuous variables. Chisquare tests were used to assess associations between categorical variables such as education level and PPE usage. Pearson correlation analysis was employed to examine the relationship between farming experience and spray frequency. Statistical significance was set at p<0.05 for all analyses.

Results

The demographic analysis revealed that the majority of respondents were male (62.5%), aged between 36 and 50 years (45.8%), and had attained secondary education (42.1%). The average farming experience was 12.4 years (SD = 6.8), and the mean farm size under tomato cultivation was 0.8 hectares (SD = 0.4).

Discussion

The predominance of organophosphate insecticides among smallholder tomato growers in central Kenya aligns with findings from earlier investigations conducted across East Africa. The high prevalence of organophosphate usage can be attributed to several factors, including their broadspectrum efficacy against multiple pest species, relatively affordable pricing, and established presence in local agrochemical markets. Similar patterns of organophosphate dominance have been documented in vegetable production systems in Ethiopia, Tanzania, and Uganda, suggesting a regional trend driven by comparable market dynamics and farmer preferences. The finding that agrochemical dealers serve as the primary information source for insecticide selection decisions raises important concerns about the quality and objectivity of pest management advice reaching smallholder farmers. Dealer recommendations may be shaped by commercial considerations such as profit margins and product availability rather than by the technical appropriateness of the insecticide for the specific pest problem. This observation is consistent with previous research conducted in West Africa, where dealer influence on pesticide selection was associated with increased rates of product misuse and over-application. The moderate positive correlation between farming experience and spray frequency suggests that long-term exposure to pest-related crop losses may reinforce a calendar-based rather than threshold-based spraying approach. More experienced farmers, having encountered repeated pest outbreaks over many seasons, may adopt a preventive spraying strategy that prioritizes frequent applications regardless of actual pest pressure levels. This behavioral pattern contrasts with the principles of integrated pest management, which advocates for insecticide application only when pest populations exceed established economic thresholds.

Ethical Considerations

This research was conducted in accordance with the ethical guidelines of Nairobi Institute of Agricultural Sciences's Institutional Ethics Review Committee. Informed consent was obtained from all participating farmers before data collection. Participation was voluntary, and respondents were assured of the confidentiality of their individual responses. No personal identifying information was included in the dataset used for analysis.

Limitations

Several limitations should be acknowledged when interpreting the findings of this research. The reliance on self-reported data may have introduced recall bias, as farmers might not accurately remember all insecticide products used or application frequencies over the survey period. Although field observations were conducted on a subset of farms to cross-validate reported practices, these observations covered only a single time point and may not capture the full range of seasonal variation in spraying behavior. The research was confined to three sub-counties within Kiambu County, and therefore the findings may not be directly generalizable to tomato production systems in other agro-ecological zones of Kenya.

Acknowledgement

AcknowledgementsThe authors express gratitude to the Kiambu County Department of Agriculture for facilitating access to farmer registration records. Appreciation is extended to the field research assistants who supported data collection activities. The cooperation of all participating tomato farmers in the three sub-counties is sincerely acknowledged.

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