Exploring the complex relationship between chemical weed control and crop performance
Soybean, often called the "miracle crop," provides a crucial source of protein and oil worldwide, forming the foundation of countless food products and animal feeds. As one of the most extensively cultivated crops globally, its productivity impacts everything from food security to agricultural economies.
Soybean is a fundamental crop for global food security and agricultural economies, making its productivity crucial.
Herbicides affect soybeans in multidimensional ways beyond simple weed elimination, influencing physiological processes.
The relationship between herbicides and crops extends beyond weed control to directly influence photosynthesis, protein production, and reproductive development in soybeans.
Applied before weeds sprout, creating a chemical barrier at the soil surface that intercepts weed seedlings during germination.
Research shows pendimethalin tank-mixed with imazethapyr proved superior against weeds 1
Target already-established weeds, allowing assessment of weed pressure before treatment with visible problem-solution approach.
Harvest-aid herbicides applied too early can severely reduce soybean yield 2
Researchers investigated how sublethal rates of auxin mimic herbicides influence soybean reproduction and nutritional value for pollinators 3 . Applications at fractions of recommended field rates (as low as 1/100x) during early vegetative stages revealed significant impacts on reproductive development.
Dicamba and florpyrauxifen-benzyl at just 1/100x of the labeled rate reduced total reproductive organs by 31% and 27% respectively, and pollen grains per anther by 25% and 18% 3 . These changes translated directly into yield reductions of 24% and 11%.
| Herbicide | Application Rate | Flower/Pod Reduction | Pollen Reduction | Yield Impact |
|---|---|---|---|---|
| Dicamba | 1/100x labeled rate | 31% | 25% | 24% reduction |
| Florpyrauxifen-benzyl | 1/100x labeled rate | 27% | 18% | 11% reduction |
| 2,4-D | 1/100x labeled rate | No significant effect | No significant effect | No significant effect |
| Quinclorac | 1/100x labeled rate | No significant effect | No significant effect | No significant effect |
Herbicides influence chlorophyll content and photosynthetic efficiency, affecting overall plant growth and development 1 .
Dry matter partitioning between stems, leaves, and reproductive organs follows predictable patterns throughout growth stages 3 .
Herbicide applications can influence protein levels in seeds while generally not affecting oil content .
Cover crops and mulching practices influenced soybean protein and oil content more than reduced herbicide rates did, highlighting the importance of considering the entire production system 5 .
PPO-inhibiting herbicides like sulfentrazon, flumioxazin, and saflufenacil provide excellent weed control but can cause significant early-season soybean injury and stand loss 4 . This creates a challenging risk-reward calculation for farmers.
Weather conditions during and after emergence play the most significant role in determining the extent of crop injury. Fields with poor drainage or ponding risk show particularly high vulnerability to herbicide injury 4 .
| Herbicide/Treatment | Weed Control Efficacy | Crop Safety | Key Considerations |
|---|---|---|---|
| Pendimethalin + Imazethapyr | Superior | Good | More effective than pendimethalin alone 1 |
| Ethalfluralin | High | Good | Recommended at 2 L.ha⁻¹ for effective control |
| PPO-inhibitors | High | Causes early injury | Recovery by 28 days; no yield impact 4 |
| Dicamba (sublethal) | N/A | Poor | Reproductive development affected 3 |
Scientists evaluate how herbicides affect soybean seed viability and seedling development by tracking germination percentages and measuring hypocotyl and primary root lengths 2 .
Glyphosate applications at certain growth stages can reduce normal seedling percentages
Using specialized protocols like the Lowry method for protein measurement and Hilcox-Israelstam techniques for chlorophyll extraction 1 .
These measurements reveal how herbicides influence fundamental plant processes
Researchers apply herbicides at standardized growth stages (R3-R8) to determine crop sensitivity at different developmental phases 2 .
Soybean sensitivity decreases as plants mature
By regularly harvesting plant samples and separating them into stems, leaves, and reproductive structures 3 .
Documents how herbicides influence dry matter accumulation
| Research Method | What It Measures | Key Findings |
|---|---|---|
| Reproductive organ counting | Flower and pod production | Dicamba reduced reproductive organs by 31% at 1/100x rate 3 |
| Pollen grain counting | Pollen grains per anther | Florpyrauxifen-benzyl reduced pollen by 18% 3 |
| Dry matter partitioning | Biomass allocation to plant parts | No herbicide effect on partitioning patterns 3 |
| Seed germination tests | Seed viability and normal development | Glyphosate reduced normal seedlings at R5-R7 stages 2 |
The relationship between herbicides and soybeans extends far beyond simple weed control. These chemical tools interact with crop physiology in nuanced ways—influencing everything from photosynthetic efficiency and protein content to flower formation and pollen production.
The emerging picture reveals a sophisticated interplay where herbicide chemistry, application timing, environmental conditions, and genetic factors collectively determine outcomes. While herbicides remain essential for profitable soybean production, their optimal use requires understanding these complex interactions.