What Are Herbicides?

To understand herbicides, it’s important to first understand weed control. Weeds are unwanted plants that grow alongside crops. They compete with crops for water, nutrients, sunlight, and space. Weeds can also attract harmful insects and fungi, which damage crops and reduce yields.

A Brief History of Weed Control

Before herbicides became common, people controlled weeds through:

  • Hand weeding

  • Using cover crops

  • Changing soil pH or fertility

  • Applying sea salt, oils, or industrial by-products

During World War II, researchers developed modern herbicides that could kill weeds without harming crops. Since then, herbicides have become essential in modern agriculture and other industries that require vegetation control.

Use of Herbicides

Herbicides are mainly used in agriculture but also in industries like landscaping, railways, and construction to remove unwanted vegetation. Their benefits include:

  • Reducing competition for light, water, and nutrients

  • Improving crop yield and quality

  • Preventing equipment damage during harvesting

  • Reducing pest and disease risks

  • Preventing contamination of water sources

Farmers use herbicides at different crop stages. For example:

  • Before planting (to prepare weed-free soil)

  • After weeds appear (using selective herbicides that don’t harm crops)

How Herbicides Work

Herbicides control or kill weeds by disrupting their growth. They are effective in small amounts and work in two main ways:

1. Systemic (Translocated) Herbicides

  • Absorbed by leaves or roots

  • Move through the plant’s system

  • Kill the entire plant, including roots

2. Contact (Non-Systemic) Herbicides

  • Kill only the part of the plant they touch

  • Work quickly but may need multiple applications

  • Less effective on perennial (long-living) weeds

Types of Herbicides

Herbicides can be grouped in different ways depending on how they work and how they’re used:

A. Based on Specificity

  • Selective Herbicides
    Target specific weeds without harming crops (commonly used in agriculture)

  • Non-Selective Herbicides
    Kill all plants they touch (used in industrial areas or land clearing)

B. Based on Application Method

  • Soil-Applied Herbicides
    Applied to soil and absorbed by weed roots or shoots; need proper placement and moisture

  • Foliar-Applied Herbicides
    Sprayed directly on weed leaves and absorbed by surface tissues

C. Based on Timing of Application

  • Pre-Plant Herbicides
    Used before planting crops to clear existing weeds

  • Pre-Emergence Herbicides
    Applied before weed seedlings emerge from soil

  • Post-Emergence Herbicides
    Used after weeds have grown; may need multiple applications and are less effective in rain

Advantages of Herbicides

Herbicides offer many benefits over manual or mechanical weed control:

  • Can be used before weeds emerge
    Reduces competition during early crop development

  • Work in all crop types and arrangements
    Reach areas that machines can’t, like between rows or closely spaced plants

  • Effective on deep-rooted weeds
    Prevent regrowth that might happen after mechanical removal

  • Long-lasting effects
    Keep fields weed-free for extended periods

  • Kill weeds similar in appearance to crops
    Help identify and remove weeds that look like crops but are genetically different