How Malathion and Sevin Affect Your Soil and Salad Greens
Scientific insights into the double-edged effects of common pesticides on garden rocket and soil health
Imagine this: you've discovered hungry insects devouring your prized garden rocket (also known as arugula). You reach for a pesticide to save your crop, but could that same solution be secretly affecting your plant's health and your soil's future fertility? This isn't just a theoretical question—scientific research reveals that pesticides can have surprising, double-edged effects on the very plants we're trying to protect 2 .
Recent studies conducted at the Sudan University of Science and Technology have examined this exact scenario, investigating how two common pesticides—Malathion and Sevin—affect not just destructive pests but also the growth of garden rocket and the soil it grows in 2 7 .
The findings reveal a complex relationship that every home gardener and commercial grower should understand. While we might assume these chemicals simply eliminate pests then disappear, the reality is far more interesting—they can actually change how plants grow and alter soil chemistry in ways both beneficial and concerning.
Before we dig into the research, let's understand our main subjects: Malathion and Sevin.
Malathion is an organophosphate insecticide that works by attacking the nervous systems of insects. It's been used for decades against a wide range of pests from mosquitoes to agricultural insects. Malathion doesn't just disappear after application—it can persist in soil and potentially affect soil organisms .
Sevin (with the active ingredient carbaryl) belongs to the carbamate family, which also targets insect nervous systems. It's a popular choice for home gardeners and farmers alike against pests on vegetables, fruits, and ornamentals. While effective, its residual effects on plants and soil have been less understood—until now.
Both pesticides work through similar mechanisms, but as we'll see, their impacts on plants and soil can differ significantly.
| Characteristic | Malathion | Sevin |
|---|---|---|
| Chemical Class | Organophosphate | Carbamate |
| Mode of Action | Nervous system disruptor | Nervous system disruptor |
| Common Uses | Mosquitoes, agricultural pests | Vegetables, fruits, ornamentals |
| Soil Persistence | Moderate | Moderate to High |
| Recommended Dose (Study) | 450kg/ha | 450kg/ha |
To understand how these pesticides really affect our gardens, researchers designed a careful experiment using garden rocket (Eruca sativa L.), a popular peppery green enjoyed in salads worldwide 2 .
The researchers followed a systematic approach:
The study was conducted at the College of Agricultural Studies farm, using identical growing conditions for all garden rocket plants to ensure fair comparisons.
The plants were divided into different groups receiving Malathion, Sevin, or no pesticide (control group).
Researchers tracked plant height, leaf count, leaf area, fresh weight, and soil nitrogen content over time.
No pesticide treatment
Recommended dose: 450kg/ha
Recommended dose: 450kg/ha
The findings revealed significant differences between the treated and untreated plants, with some outcomes defying common assumptions about these chemicals.
| Treatment | Plant Height (cm) | Number of Leaves | Leaf Area (cm²) | Fresh Weight (g) |
|---|---|---|---|---|
| Control (No Pesticide) | 45.35 | 14 | 13.71 | 40.30 |
| Malathion (Recommended Dose) | ~48* | 21 | 11.00 | ~43* |
| Sevin (Recommended Dose) | 52.10 | 21 | 12.00 | ~47* |
*Note: Exact weight values for some treatments were not provided in the research paper, but the study reported Sevin gave "positively affected" weight compared to control 2 .
The data reveals a striking pattern: both pesticides actually enhanced certain growth aspects compared to untreated plants. Sevin in particular produced the tallest plants at 52.1 cm—significantly taller than the control group's 45.35 cm. Both pesticides resulted in more leaves (21 versus 14 in controls), though leaf area showed more complex effects.
The effects weren't limited to what happened above ground. The soil itself underwent chemical changes, particularly in nitrogen content 2 . Both pesticides significantly increased the total nitrogen percentage in the soil, though the study didn't find significant changes to soil pH or salinity levels.
This nitrogen boost might explain some of the growth enhancements observed, as nitrogen is a crucial nutrient for plant development, especially for leafy greens like garden rocket that require ample nitrogen for vigorous leaf production 4 .
Why would pesticides affect soil nitrogen? The researchers didn't definitively answer this question, but there are several scientific possibilities:
Pesticides might affect nitrogen-fixing bacteria or other microorganisms involved in the nitrogen cycle, potentially changing how nitrogen is processed and made available to plants 5 .
The chemicals might influence how plants absorb and utilize nitrogen from the soil.
With fewer pests attacking them, plants might be able to utilize soil nutrients more efficiently.
This unexpected effect on soil nitrogen demonstrates how chemical interventions can ripple through the entire plant-soil system in ways we're only beginning to understand.
Conducting rigorous research on pesticides and soil requires specific tools and methodologies. Here are key components from the scientific toolkit:
| Research Material | Primary Function | Specific Application in Pesticide-Soil Studies |
|---|---|---|
| Soil Sampling Tools | Collect representative soil samples | Obtain consistent samples from treatment and control plots for comparative analysis |
| pH Testing Equipment | Measure soil acidity/alkalinity | Determine whether pesticides alter soil pH balance 1 |
| Soil Test Extractants | Assess nutrient availability | Evaluate how pesticides affect nutrient availability to plants 6 |
| Colorimetric Test Kits | Quantify specific nutrients | Measure changes in nitrogen, phosphorus, potassium levels post-pesticide application |
| Digital Calipers | Precise physical measurements | Document plant height, leaf dimensions with high accuracy |
| Analytical Balances | Measure biomass changes | Detect subtle differences in plant weight due to pesticide treatments |
The implications of this research extend far beyond garden rocket. Similar studies have examined these pesticides on other crops:
Showed comparable patterns, with Sevin at recommended doses increasing plant height and weight 5 .
Confirmed the trend, again showing Sevin enhancing growth parameters at proper application rates 7 .
Demonstrated that while recommended doses might benefit plants, excessive concentrations can dramatically reduce growth 5 .
This last point is crucial—the same study that found benefits at recommended doses showed that higher pesticide concentrations could be detrimental, reducing plant height by nearly 50% and fresh weight by 67% in carrots compared to controls 5 .
These findings point toward what we might call the Precision Principle in pesticide use: outcomes depend critically on exact dosage, specific pesticide chemistry, plant species, and growing conditions.
While this research shows that pesticides can be used effectively, the findings also highlight why many gardeners and farmers are exploring integrated pest management approaches that reduce chemical reliance 8 . These include:
The future of sustainable gardening and farming lies in understanding these complex interactions and working with, rather than against, natural systems while using science-informed interventions when truly needed.
The relationship between pesticides, plants, and soil is far more complex than we often assume. The research on Malathion and Sevin reveals that these chemicals don't just disappear after killing pests—they enter into a dynamic relationship with our plants and soil, with effects that can surprise us.
As we've seen, pesticides at recommended doses can sometimes enhance growth, likely through subtle effects on soil chemistry and plant processes. But this doesn't mean we should view them as growth promoters—rather, it underscores how much we still have to learn about the complex chemistry happening beneath our feet and in our plants.
The most important lesson for gardeners might be this: understand the tools you use, respect their power, and always remember that in gardening and agriculture, the simplest solutions—healthy soil, appropriate plant selection, and close observation—often prove most effective in the long run.
The next time you spot insects on your garden rocket, you'll have a more nuanced understanding of the potential impacts of your intervention—not just on the pests, but on your plants and soil as well.