Herbicides play a key role in modern agriculture, helping farmers control unwanted plants (weeds) that compete with crops for nutrients, water and space.
However, their use must be approached with care to safeguard people, crops and the environment. Weed Scientist Ncomiwe Maphalala shares key insights and guidelines for the responsible use of herbicides in Eswatini.
Purpose of herbicide use
The primary goal of herbicide application is to achieve effective weed management while minimising unintended harm.
According to Maphalala, herbicide decisions should:
- Consider the overall impact on non-target organisms, crops and the environment.
- Align with conservation and management goals for the specific site.
- Prioritise the health and safety of farmers, applicators and surrounding communities.
- Ensure that the herbicide does more good than harm.
What are herbicides?
Herbicides are chemical substances designed to control or eliminate unwanted plants. They work by targeting specific processes within weeds, either inhibiting growth or causing plant death. By reducing weed competition, herbicides enhance crop productivity and yield.
Classification of herbicides
Herbicides are classified based on their selectivity, timing, mode of action and residual effect. Understanding these categories helps farmers choose the right product for each situation.
1. Selective vs non-selective herbicides
Selective herbicides: Target specific weeds while leaving crops unharmed.
Examples: 2.4-D, Bladex Super, Dual Gold.
Non-selective herbicides: Kill all vegetation, including crops.
Examples: Glyphosate, Paraquat.
2. Pre-emergent vs post-emergent herbicides
Pre-emergent: Applied before weeds germinate to form a protective barrier.
Examples: Pendimethalin, Dual Gold, Atrazine.
Post-emergent: Used on actively growing weeds.
Examples: Bladex, Basagran, 2.4-D.
3. Contact vs systemic herbicides
Contact: Kill only the parts of the plant they touch; ideal for quick control.
Examples: Paraquat, Basagran.
Systemic: Absorbed and circulated throughout the plant to kill it entirely.
Examples: Glyphosate, Bladex, Alachlor.
4. Residual vs non-residual herbicides
Residual: Remain active in soil for long-term weed control.
Examples: Atrazine, Callisto, Imazapyr.
Non-Residual: Break down quickly after application, suitable for short-term control.
Examples: Pendimethalin, Dual Gold.
Factors to consider when choosing a herbicide
Selecting the right herbicide involves evaluating several key factors:
1. Type of weed: Identify whether weeds are broadleaf, grassy, annual or perennial to choose a compatible herbicide.
2. Mode of action: Understand how the herbicide works, whether it’s systemic, contact, pre-emergent or post-emergent.
3. Crop type: Ensure compatibility with the crop to avoid damage. Use selective herbicides for lawns and crops and non-selective ones for hard surfaces or before planting.
4. Environmental impact: Assess the herbicide’s potential effects on soil, water and nearby plants. Avoid products that could contaminate water sources or harm non-target vegetation.
5. Timing of application: Apply herbicides when weeds are actively growing and weather conditions are calm and dry to avoid drift or wash-off.
6. Health and safety: Always wear protective equipment such as gloves, masks and goggles. Observe re-entry intervals stated on product labels.
7. Herbicide resistance: Rotate herbicides with different modes of action and integrate other weed control methods to prevent resistance.
8. Cost and availability: Consider product price, accessibility and long-term cost-effectiveness before purchase.
Best practices for herbicide application
To maximise herbicide efficiency and safety:
- Read and follow label instructions carefully for dosage and safety. Look for key sections like product information, active ingredients, hazard statements, precautionary statements, application instructions and storage/disposal instructions.
- Wear protective gear to reduce exposure.
- Calibrate spraying equipment to ensure even coverage.
- Apply in suitable weather to prevent drift and environmental contamination.
- Avoid overuse, which can harm crops and soil health.
Advantages of using herbicides
Efficiency: Saves time and labour compared to manual weeding.
Cost-effective: Reduces crop loss due to weed competition.
Precision: Targets specific weeds without affecting crops.
Flexibility: Can be used pre- or post-emergence, offering control throughout the season.
Challenges and considerations
While herbicides are valuable tools, misuse can cause serious harm. Issues such as resistance development, environmental pollution and health risks have emerged from improper application.
Maphalala urges farmers to use herbicides responsibly, always adhering to label instructions and integrating sustainable weed management practices.
Herbicides, when used correctly, remain essential for effective weed management and improved agricultural productivity. Responsible application protects farmers, crops and the environment, ensuring long-term sustainability in Eswatini’s agricultural sector.
For more information and advice, contact Maphalala at maphalalancomiwe@gmail.com.
Leave a comment