Research reveals that while preventative insecticides reduce seedling injury, they consistently fail to increase yields in both Bt and non-Bt corn systems.
In the endless green seas of Mid-Atlantic cornfields, an invisible battle rages beneath the soil and among the leaves.
For decades, farmers have armed their crops with multiple layers of protection—genetically engineered Bt corn, neonicotinoid seed treatments, and pyrethroid insecticides—all deployed preventatively against potential insect threats. But what if this overwhelming firepower is largely unnecessary?
Recent research from the University of Maryland reveals a surprising truth: while preventative insecticides do reduce some seedling injury, they consistently fail to increase yields in both Bt and non-Bt corn systems 1 . This groundbreaking discovery challenges decades of conventional agricultural practice and suggests we may be dramatically over-insecticiding our crops.
Preventative insecticides reduce pest injury but don't translate to increased corn yields, questioning their economic value in many farming scenarios.
Modern corn production employs an impressive arsenal of pest management tools, each with its own mechanism of action and target pests:
Genetically modified varieties containing genes from Bacillus thuringiensis that produce proteins toxic to specific insect pests 1 .
Chemicals like clothianidin applied as seed coatings, making the plant toxic to pests as it grows 7 .
Insecticides like bifenthrin applied directly into the planting furrow during seeding 7 .
These approaches are often used in combination, creating what entomologists call "redundant pest control"—multiple layers of protection targeting the same insect pests. While this might seem like a conservative, better-safe-than-sorry approach, it comes with significant costs both economic and environmental.
To evaluate the real-world value of these preventative treatments, researchers from the University of Maryland's Hamby Lab conducted a comprehensive three-year study (2020-2022) across three research farms in Maryland representing different growing regions 3 7 .
The findings from this extensive study revealed a fascinating disconnect between visual indicators of success (reduced pest injury) and actual economic outcomes (yield):
| Treatment | Bt Hybrid - Injury Reduction | Bt Hybrid - Stand Improvement | Non-Bt Hybrid - Injury Reduction | Non-Bt Hybrid - Stand Improvement |
|---|---|---|---|---|
| Neonicotinoid Seed Treatment | Significant | Significant | Significant | None |
| In-Furrow Pyrethroid | None | None | Significant | None |
| Untreated Control | Baseline | Baseline | Baseline | Baseline |
| Treatment | Bt Hybrid | Non-Bt Hybrid |
|---|---|---|
| Neonicotinoid Seed Treatment | No significant increase | No significant increase |
| In-Furrow Pyrethroid | No significant increase | No significant increase |
| Untreated Control | Baseline | Baseline |
Perhaps most surprisingly, even in the site-year with the most extensive insect injury, insecticide treatments failed to produce measurable yield gains 1 . This suggests that corn plants possess a remarkable ability to compensate for early-season damage without impacting final productivity.
| Pest Category | Frequency of Economic Damage | Most Common Species |
|---|---|---|
| Soil Pests (wireworms, grubs) | Low (1 of 9 site-years) | Not specified |
| Lepidopteran Pests (cutworms, armyworms) | Low (2 of 9 site-years) | Black cutworm, armyworm |
| Slugs | Moderate (3 of 9 site-years) | Various slug species |
| Above-ground Chewing Insects | Low (1 of 9 site-years) | Flea beetles, Japanese beetles |
The research also examined whether insecticides might disrupt natural pest control mechanisms by harming beneficial insects. Surprisingly, they found that insecticide treatments did not affect predation on slugs or increase slug damage over the course of the study 7 . This contrasts with findings from soybean systems where neonicotinoids had previously been shown to disrupt biological control of slugs.
The implications of this research extend far beyond farm economics. Preventative insecticides, particularly neonicotinoids, have come under increasing scrutiny due to their potential effects on:
Numerous studies have linked neonicotinoids to declines in bee populations and other beneficial insects 6 .
These systemic insecticides can persist in soil and water, potentially disrupting soil microbial communities and nutrient cycling.
The broad-spectrum activity of these chemicals can harm beneficial insects that provide natural pest control services.
"Implementing efficient economically and environmentally sustainable corn pest management requires a thorough understanding of the contributions of each component of the pest control system" — Dr. Kelly Hamby, principal investigator 1
Her team's work demonstrates that in many cases, the environmental costs of preventative insecticides may be incurred without any compensatory yield benefits.
The overuse of preventative insecticides isn't just potentially wasteful—it may actually undermine their long-term effectiveness. Insect resistance to both Bt traits and chemical insecticides is a growing concern in agricultural entomology .
In Minnesota, resistance to Bt proteins has been documented in western corn rootworm populations across multiple counties .
Resistance to crop rotation has emerged in both western and northern corn rootworm variants, complicating management strategies that have been reliable for decades.
The practice of stacking multiple pest control technologies—Bt traits plus seed treatments plus in-furrow insecticides—may actually accelerate resistance development by creating intense selection pressure that favors resistant insect variants. This arms race often ends badly for farmers, as pests evolve to overcome even the most sophisticated defenses.
Based on their findings, the researchers recommend a more nuanced approach to corn pest management:
Monitor fields for actual pest presence and economic injury levels before treatment 2 .
Implement treatments only when pest populations exceed economic thresholds 2 .
Protect beneficial insects by reducing broad-spectrum insecticide use 7 .
Implement cultural controls like crop rotation and planting date adjustments .
| Research Tool | Function | Application in This Study |
|---|---|---|
| Poncho 250 | Neonicotinoid seed treatment (clothianidin) | Systemic protection against early-season pests |
| Capture LFR | Pyrethroid insecticide (bifenthrin) | In-furrow application for soil and seedling pests |
| Pheromone Traps | Species-specific insect monitoring | Tracking migratory pest populations |
| Latin Square Design | Statistical experimental layout | Minimizing spatial variability in field trials |
This approach aligns with the principles of Integrated Pest Management (IPM), which emphasizes using multiple complementary strategies rather than relying solely on chemical controls.
The University of Maryland study challenges long-standing practices in corn production and highlights the complex relationship between pest injury and crop yield.
While our instinct might be to protect crops at all costs, the research suggests that we may be overprotecting them—incurring unnecessary expenses and environmental impacts without improving the bottom line.
As agricultural systems face increasing pressure to become more sustainable, studies like this provide valuable guidance for balancing productivity with environmental stewardship. The path forward appears to lie not in layering on more insecticides, but in developing more sophisticated, tailored approaches that respond to actual pest threats rather than theoretical ones.
The silent shield of preventative insecticides, it turns out, may be too much of a good thing. Sometimes, the best protection is knowing when to hold back and let natural systems do their work.
Consult your local extension service or visit the University of Maryland Department of Entomology website for information on sustainable pest management practices.
References will be listed here.