Why Preventative Insecticides Often Fail to Boost Yields
Imagine a cornfield in mid-summer—lush green stalks swaying in the breeze, promising a bountiful harvest. What you can't see are the invisible chemical defenses coating each seed, intended to protect the crop from underground invaders. For decades, preventative insecticide treatments have become standard practice in corn production, with growers spending millions annually on these insurance policies against pest damage. But what if this widespread agricultural practice is often unnecessary—an expensive solution without a problem?
Recent research from the University of Maryland reveals a surprising truth: while neonicotinoid seed treatments and in-furrow pyrethroids do reduce seedling injury in both genetically engineered (Bt) and conventional corn hybrids, they consistently fail to increase yields across the Mid-Atlantic region.
This groundbreaking study challenges long-held assumptions about corn pest management and suggests that farmers could significantly reduce input costs while maintaining productivity—if we're willing to rethink our approach to protection 1 3 .
Modern corn production employs multiple layers of insect protection:
Preventative insecticides don't distinguish between friend and foe. Their non-target effects can disrupt agricultural ecosystems by:
The economic rationale for these treatments has been further undermined by regional pest suppression associated with widespread Bt crop adoption. Area-wide planting of Bt field corn has dramatically reduced populations of pests like European corn borer and corn earworm—benefiting even vegetable growers of peppers, green beans, and sweet corn through reduced damage and insecticide applications 7 .
From 2020 to 2022, University of Maryland researchers conducted a comprehensive field study across three research farms representing Maryland's diverse growing conditions: Keedysville (Western Maryland), Beltsville (Central Maryland), and Queenstown (Eastern Shore) 2 5 .
The team established a meticulous experimental design:
The research team documented not just final harvest numbers but multiple indicators of crop health and ecosystem impact:
The comprehensive study generated a wealth of data that challenges conventional wisdom about corn insect management.
| Hybrid Type | Treatment | Reduction in Insect Damage | Stand Improvement | Yield Increase |
|---|---|---|---|---|
| Bt Corn | Untreated Control | Baseline | Baseline | Baseline |
| Neonicotinoid (Poncho) | 62% reduction | 8% improvement | No significant increase | |
| Pyrethroid (Capture) | No significant reduction | No improvement | No significant increase | |
| Non-Bt Corn | Untreated Control | Baseline | Baseline | Baseline |
| Neonicotinoid (Poncho) | 66% reduction | No improvement | No significant increase | |
| Pyrethroid (Capture) | ~50% reduction | No improvement | No significant increase |
| Factor | Neonicotinoid Seed Treatment | In-Furrow Pyrethroid |
|---|---|---|
| Approximate Cost per Acre | $8-12 | $10-15 |
| Target Pests | Wireworms, white grubs, seedcorn maggots, some early-season foliar pests | Similar spectrum with slightly different efficacy |
| Yield Benefit in Study | None observed | None observed |
| Non-Target Impacts | Potential harm to slug predators, pollinators | Potential harm to natural enemies |
| Situational Value | Possibly valuable in fields with known soil pest history | Possibly valuable against specific pests |
| Overall ROI in Mid-Atlantic | Negative (cost without benefit) | Negative (cost without benefit) |
| Pest Type | Bt Corn (% plants damaged) | Non-Bt Corn (% plants damaged) | Economic Threshold |
|---|---|---|---|
| Armyworms | 0-5.4% | 0-22.9% | 35% damaged plants |
| Cutworms | 1-6.3% | 0.5-3.8% | 10% damaged plants |
| Soil Pests (combined) | <5% at most sites | <5% at most sites | Varies by specific pest |
| Slug Damage | Generally low except one site-year (42% damage) | Not established, but plants recovered | |
The most surprising finding emerged from the slug damage data: even when 42% of seedlings showed slug damage at one location in 2021, corn yields didn't suffer because plants outgrew the early injury—as long as their growing points remained intact. This resilience mirrors corn's ability to recover from hail damage 6 .
Field ecology research requires specialized approaches to measure complex interactions. Here are key tools and methods used in this study:
| Research Tool | Function | Significance in Study |
|---|---|---|
| Poncho 250® (clothianidin) | Neonicotinoid insecticide seed treatment | Evaluate efficacy against early-season pests |
| Capture LFR® (bifenthrin) | Pyrethroid insecticide for in-furrow application | Compare alternative delivery method and spectrum of control |
| Sentinel caterpillars | Pre-measured prey items placed in field | Quantify biological control services by measuring predation rates |
| Pitfall traps | Container traps sunk level with soil surface | Capture and quantify ground-dwelling predators (beetles, spiders) |
| Leaf damage assessment grids | Standardized measuring templates | Quantify area of leaf tissue consumed by pests |
| Pheromone traps | Species-specific attractants for moths | Monitor adult populations of key pest species (corn earworm, armyworms) |
The researchers also employed advanced statistical modeling to separate treatment effects from variables like weather patterns, soil conditions, and location-specific factors that might influence outcomes 2 .
The study's findings suggest that prophylactic insecticide applications represent unnecessary expenses for many Mid-Atlantic corn growers. With insecticide treatments costing $8-15 per acre without consistent yield benefits, eliminating these inputs could improve profitability—especially important when corn prices are low 5 .
The research supports a shift toward scouting-based decision making—monitoring fields for actual pest presence rather than assuming insurance treatments will pay off. Economic thresholds exist for many corn pests (e.g., treat when 35% of plants show armyworm damage or 10% show cutworm damage), and these were rarely approached in the study, even in completely untreated plots 6 .
Cutting unnecessary insecticide applications provides environmental benefits:
The study found that neither insecticide treatment significantly reduced predation rates on sentinel caterpillars—a positive sign that biological control remained functional—but previous research has documented negative impacts on natural enemies from these chemicals 6 .
While the study focused on the Mid-Atlantic, its findings may not apply equally everywhere. Research from the Mid-South (Arkansas, Louisiana, Mississippi, and Tennessee) has shown that neonicotinoid seed treatments provided significant yield benefits in 8 out of 14 years . This highlights the importance of region-specific recommendations rather than one-size-fits-all approaches.
The University of Maryland study adds to a growing body of evidence that preventative insecticides often provide insufficient economic return in many corn production systems, especially where pest pressure is typically low to moderate. While these treatments do reduce seedling injury—particularly neonicotinoid seed treatments—the conversion of healthier seedlings to higher yields proves elusive in the Mid-Atlantic region 1 3 6 .
The research advocates for a more nuanced approach that combines:
As agricultural sustainability becomes increasingly important—both economically and environmentally—this research helps pave the way toward more selective, sophisticated approaches to pest management that protect both profits and ecosystems.
The findings remind us that sometimes the best protection comes not from what we add to our fields, but from what we wisely choose to leave out.
This article was based on research conducted by the Hamby Lab at the University of Maryland and published in Pest Management Science 1 . For more information on sustainable agriculture research, visit the Department of Entomology at the University of Maryland.