Types of Herbicides: Uses, Benefits, and How They Work

Herbicides are chemicals used to control or eliminate unwanted plants (weeds) that compete with crops, gardens, and lawns for nutrients, water, and sunlight. These substances are essential in modern agriculture, as they help maintain healthy crops and improve yields. Herbicides can be categorized based on their chemical composition, mode of action, and selectivity. Understanding the types of herbicides, their uses, benefits, and how they work can provide insights into their role in agriculture and gardening.

1. Selective Herbicides

Selective herbicides target specific weeds without harming the desired crops. These herbicides are formulated to act on certain plant species while being safe for others. For example, certain herbicides may only affect broadleaf weeds and leave grasses unharmed, or vice versa. Selective herbicides are crucial in agricultural fields where crops like wheat, corn, and soybeans are grown alongside weeds that need to be controlled. By preventing weeds from competing with crops, these herbicides help in maximizing crop yields.

Examples: MCPA, Dichlorprop, Triclopyr

Uses: Selective herbicides are widely used in cereal, soybean, and vegetable crops.

Benefits: They reduce competition between crops and weeds, promoting healthier crop growth and increased yields.

How They Work: Selective herbicides often disrupt specific biochemical pathways in the target plants, such as inhibiting protein synthesis or photosynthesis, while leaving the crops unaffected due to differences in the plants' metabolic processes.

2. Non-Selective Herbicides

Non-selective herbicides kill or damage all plants they come into contact with, making them effective in clearing entire areas of vegetation. These herbicides are commonly used to clear fields, industrial sites, roadsides, and even for managing invasive plant species.

Examples: Diquat, Paraquat, Glufosinate

Uses: Non-selective herbicides are often used in land preparation, weed control in orchards, and to manage weeds in non-crop areas like railroads or highways.

Benefits: They are highly effective for clearing large areas of unwanted vegetation and controlling invasive species.

How They Work: Non-selective herbicides typically work by interfering with the plant's ability to produce food through photosynthesis or causing rapid cell death, affecting both the weeds and any surrounding plants they come in contact with.

3. Pre-Emergence Herbicides

Pre-emergence herbicides are applied before the weed seeds have germinated, forming a barrier that prevents weed growth. These herbicides are particularly useful in controlling annual weeds in crops, lawns, and gardens.

Examples: Acetochlor, Alachlor, Metolachlor, Pendimethalin

Uses: Commonly used for controlling weeds in crops like maize, soybeans, and cotton, as well as in turf management.

Benefits: By preventing weeds from emerging, these herbicides reduce the need for later post-emergence treatments and minimize the competition between weeds and crops.

How They Work: Pre-emergence herbicides typically inhibit seedling development by affecting root formation or seedling growth as soon as the weed seeds germinate.

4. Post-Emergence Herbicides

Post-emergence herbicides are applied after weeds have emerged and are actively growing. These herbicides are typically more effective against established weeds and can be used selectively or non-selectively, depending on the formulation.

Examples: Glyphosate, Glufosinate, 2,4-D, and Dicamba

Uses: Post-emergence herbicides are used in crop fields, lawns, gardens, and in areas where mature weeds need to be controlled.

Benefits: They are effective at targeting and eliminating mature, established weeds without affecting crops.

How They Work: These herbicides often interfere with the plant’s metabolic functions, such as protein synthesis or growth regulation, leading to the death of the weed. Some post-emergence herbicides are absorbed through the foliage, while others may be absorbed through the roots.

5. Systemic Herbicides

Systemic herbicides are absorbed by plants and transported through the plant's vascular system to affect the entire plant. These herbicides are effective in controlling both the roots and the shoots of the weeds, often resulting in complete elimination of the plant.

Examples: Dicamba, Picloram, Amitrole, 2,4 D and Glyphosate

Uses: Systemic herbicides are commonly used for controlling perennial weeds, woody plants, and invasive species.

Benefits: They provide long-lasting control, often with a single application, and are highly effective against deep-rooted weeds.

How They Work: After being absorbed, systemic herbicides move throughout the plant, disrupting various processes such as energy production, growth regulation, or cell division, leading to the plant's death.

6. Non-Systemic Herbicides

Non-systemic herbicides, also known as contact herbicides, act upon the parts of the plant they directly contact. While they are often fast-acting, providing quick results, they may not offer long-term control. These herbicides are suitable for spot treatments and are commonly employed in situations where rapid control of annual weeds is necessary.

Examples: Paraquat, Diquat

Uses: Non-systemic herbicides are highly effective for controlling annual weeds. They are ideal for vegetation control in non-crop areas like driveways and gravel paths, and perfect for spot treatments, targeting isolated weed patches without harming surrounding plants or larger garden areas.

Benefits: One of the main advantages of non-systemic herbicides is their speed. As they target the plant’s outer cells, they often produce rapid visual effects, killing or damaging the foliage within a short period

How They Work: When applied to a plant, non-systemic herbicides affect only the sprayed areas. This means they typically kill or damage the foliage, but not the roots or internal plant systems. The plant may yellow, wither, or burn within hours or a few days.

Conclusion

Herbicides play a critical role in modern agriculture and land management by preventing weed growth, reducing competition for resources, and improving crop productivity. Whether selective or non-selective, pre-emergence or post-emergence, and systemic or contact, herbicides work in different ways to suit specific needs. While their benefits in controlling weeds are clear, it is essential to use herbicides judiciously to avoid negative environmental impacts, such as soil degradation, water contamination, and harm to non-target species. Proper application and adherence to guidelines are key to ensuring that herbicides are used safely and effectively.