Introduction

Herbicides are essential tools in modern agriculture, but their unintended impact on pollination is a growing concern. Recent research by Dummer et al. (2025) has revealed that glyphosate and 2,4-D, two commonly used herbicides, can severely impair olive pollen germination, raising serious questions about their effects on fruit set and overall productivity in olive groves.

How Herbicides Affect Olive Pollen Germination

Key Research Findings (Dummer et al., 2025):

• Glyphosate and 2,4-D significantly reduce pollen viability at even low concentrations.
• A low dose of glyphosate (0.19 g L⁻¹) reduced pollen germination by 44% in Arbequina and 38.2% in Koroneiki olives.
• Higher doses (1.92 g L⁻¹ glyphosate and all tested doses of 2,4-D) caused 100% pollen inviability, meaning no germination occurred.
• Herbicide drift during flowering could lead to lower fruit set, reducing olive yields.

These findings highlight a previously overlooked risk: routine herbicide use in or near olive groves may disrupt pollination and lower production.

Mechanisms of Herbicide Damage to Pollen

Glyphosate: Disrupting Essential Pathways

Glyphosate inhibits 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), a key enzyme in the shikimic acid pathway, which is essential for the production of aromatic amino acids (Duke, 2021).

• Without these amino acids, pollen loses viability, leading to reduced germination rates.
• Glyphosate is widely used in olive orchards for weed control (Peragón & Amores-Escobar, 2018), increasing the risk of exposure to pollen during the critical flowering period.

2,4-D: Mimicking and Disrupting Plant Hormones

2,4-D is a synthetic auxin that mimics indoleacetic acid (IAA), a natural plant hormone. While auxins regulate normal plant growth, excessive exposure to synthetic auxins disrupts plant cell function (Grossmann, 2010).

• Even at low doses (0.16 g L⁻¹ and 1.61 g L⁻¹), 2,4-D completely inhibited olive pollen germination (Dummer et al., 2025).
• 2,4-D causes membrane damage, abnormal pollen tube growth, and cellular toxicity, preventing successful fertilisation.

Implications for Olive Growers

1. Herbicide Drift Poses a Real Threat

Herbicide drift- where chemicals move beyond their intended target – occurs frequently in agricultural areas, especially when spraying is done during blooming seasons (Bish et al., 2021).

• Many crops, including soybeans and wheat, are treated with herbicides in spring—coinciding with olive tree flowering (Aguilera et al., 2015).
• Even low doses of airborne glyphosate or 2,4-D residues can reduce pollen germination, lowering potential fruit set.

2. Reduced Pollination = Lower Yields

Successful pollination is crucial for olive fruit development. If pollen viability is reduced by 44% or more, as observed in this study, fruit set could drop significantly, impacting overall olive production.

• The effects of herbicide exposure may not be immediately visible, leading to unexpected yield reductions over time.

3. Olive Varieties May Differ in Sensitivity

The study focused on Arbequina and Koroneiki – two widely grown olive cultivars. However, different cultivars may exhibit varying levels of sensitivity to herbicides. Further research is needed to determine if certain olive varieties are more resistant than others.

Best Practices for Olive Growers

Given these findings, olive producers should take proactive steps to protect pollination and productivity:

• Avoid herbicide applications during flowering. Plan spraying schedules to minimise exposure during peak bloom.
• Monitor herbicide drift risk. Be aware of nearby agricultural spraying activity, especially during spring pollination.
• Use precision herbicide application techniques. Avoid broadcast spraying- instead, use targeted or spot applications to reduce unintended exposure.
• Consider alternative weed management methods such as mulching, mechanical weeding, or cover crops to reduce reliance on herbicides.
• Conduct regular field assessments to monitor pollen viability in herbicide-exposed areas. If poor fruit set is observed, assess whether herbicide drift could be a factor.

Conclusion

The study by Dummer et al. (2025) provides clear evidence that glyphosate and 2,4-D negatively impact olive pollen germination, even at very low doses. Since pollen viability directly affects fruit set and yield, herbicide exposure during flowering could be a major risk to productivity.

While herbicides are essential for weed control, olive growers must implement careful management strategies to minimise risks to pollination and fruit development. Further field research is needed to assess real-world impacts beyond laboratory conditions.

Reference

Dummer, L. S., da Silva, F. L., Posso, D. A., & Mello-Farias, P. (2025). Reduction of olive pollen germination when exposed to herbicides in vitro. Semina: Ciênc. Agrár. Londrina, 46(2), 631-638. DOI: 10.5433/1679-0359.2025v46n2p631.

See more: Olive Harvesting