What Is a Weedicide?


Weedicide, also known as herbicide, is a type of chemical compound used to kill or control the growth of weeds. There are several types of weedicides available on the market, each with different modes of action and target plants. Here are some details on the most common types of weedicides, their function, and examples of each.

Contact Herbicides

Contact herbicides kill the part of the plant they come into contact with, usually the leaves or stems. They are typically used to control annual weeds or young plants but may not be effective against perennials or mature plants. These herbicides can be non-selective or selective, depending on the plant they are intended to kill.

Example: Dicamba and Paraquat

Systemic Herbicides

Systemic herbicides are absorbed by the plant and transported to all parts of the plant, including the roots and leaves. They are typically used for controlling weeds with deep roots or underground rhizomes. Systemic herbicides can be selective or non-selective, and they can be further categorized as either translocated or non-translocated.

Example: Glyphosate and Imazapic

Residual Herbicides

Residual herbicides provide long-term control of weeds by remaining active in the soil and preventing weed seeds from germinating. They can be selective or non-selective, and they can be classified based on their length of activity and the type of soil they are effective in.

Example: Atrazine and S-metolachlor

Selective Herbicides

Selective herbicides are designed to kill specific types of plants while leaving others unharmed. They are typically used for controlling weeds in lawns, gardens, and crops without damaging the desired plants. Selective herbicides can be further classified based on their target weed type and mode of action.

Example: 2,4-D and Triclopyr

Non-Selective Herbicides

Non-selective herbicides kill or damage all types of plants they come into contact with. They are typically used for controlling weeds in areas where no plants are desired, such as driveways, sidewalks, and fence lines.

Example: Glyphosate and Paraquat

Pre-Emergent Herbicides

Pre-emergent herbicides prevent weed seeds from germinating and growing by creating a barrier in the soil. They are typically used before the growing season to prevent weed growth.

Example: Dithiopyr and Pendimethalin

Post-Emergent Herbicides

Post-emergent herbicides are used to control weeds after they have already emerged from the soil. They can be selective or non-selective and can be further categorized based on their target weed type and mode of action.

Example: Clopyralid and Fluroxypyr

Organic Weedicide

Organic weedicides are alternatives to chemical weedicides that are derived from natural materials and substances. They are typically considered safer and more environmentally friendly than chemical weedicides because they are less harmful to humans, wildlife, and the environment. Here are some details on common organic weedicides and how they work −


Vinegar is a natural acid that can be used as an organic weedicide. It works by drying out the leaves and stems of the plants, causing them to wilt and die. Vinegar is typically used in a solution with water and dish soap to increase its effectiveness.

Corn Gluten Meal

Corn gluten meal is a natural byproduct of the corn milling process that has pre-emergent herbicidal properties. It works by preventing weed seeds from germinating and can be effective against annual weeds.


Salt is another natural substance that can be used as an organic weedicide. It works by dehydrating the plant and making it difficult for it to absorb water. Salt can be used as a spot treatment for weeds in cracks and crevices, but it should be used sparingly because it can also harm desirable plants and accumulate in the soil.

Citric Acid

Citric acid is a natural acid that can be used as an organic weedicide. It works by disrupting the cell membranes of the plant, causing it to wilt and die. Citric acid is typically used in a solution with water and dish soap to increase its effectiveness.

Essential Oils

Essential oils, such as clove oil and cinnamon oil, have herbicidal properties and can be used as organic weedicides. They work by disrupting the cell membranes of the plant and can be effective against both annual and perennial weeds.

Corn Gluten Hydrolysate

Corn gluten hydrolysate is a liquid form of corn gluten meal that is used as a post-emergent organic weedicide. It works by inhibiting the growth of the weed and can be effective against both annual and perennial weeds.

It is important to note that organic weedicides may not be as effective as chemical weedicides and may require multiple applications for optimal results. In addition, they should be used carefully to avoid damaging desirable plants and should be applied in accordance with label instructions. Overall, organic weedicides can be a safe and effective alternative to chemical weedicides for those who prefer a natural approach to weed control.

Mechanism of Action

The mechanism of action of weedicides varies depending on the type of chemical used. However, most weedicides work by disrupting essential metabolic processes in the plant, leading to its death. Here are some common mechanisms of action −

Photosynthesis Inhibitors

Photosynthesis inhibitors, such as triazines, inhibit the photosynthetic process in plants by preventing the absorption of light energy. Without energy from photosynthesis, the plant cannot produce food and eventually dies.

Cell Division Inhibitors

Cell division inhibitors, such as dinitroanilines, disrupt cell division in plants, which is essential for growth and reproduction. These chemicals prevent the formation of microtubules, which are essential for proper cell division, leading to abnormalities in growth and development.

Growth Regulators

Growth regulators, such as auxins, mimic or block natural plant hormones, disrupting normal growth and development. These chemicals can cause the plant to grow abnormally, leading to stunted growth, malformed leaves, and other deformities.

Respiration Inhibitors

Respiration inhibitors, such as bipyridyls, disrupt the process of respiration in plants, preventing them from producing energy. This causes the plant to become weak and eventually die.

Enzyme Inhibitors

Enzyme inhibitors, such as glyphosate, block the action of specific enzymes that are essential for plant growth and metabolism. Without these enzymes, the plant cannot perform essential metabolic processes, leading to its death.

Health and Environmental Effects

The use of weedicides can have both health and environmental effects. Here are some potential risks associated with the use of these chemicals −

Health Effects

Exposure to weedicides can cause a range of health effects in humans, including −

  • Skin irritation or rash.

  • Respiratory problems, including asthma and lung damage.

  • Headaches, dizziness, and nausea.

  • Eye irritation and damage.

  • Increased risk of certain cancers, such as non-Hodgkin lymphoma and leukemia.

Environmental Effects

Weedicides can also have negative impacts on the environment, including −

  • Soil Contamination: Weedicides can accumulate in the soil and persist for long periods, which can damage soil quality and reduce its ability to support plant growth.

  • Water Pollution: Weedicides can leach into groundwater and surface water, contaminating drinking water sources and harming aquatic life.

  • Non-target Species: Some weedicides can harm beneficial insects, birds, and mammals that may be essential to the local ecosystem.

  • Resistance: Overuse of weedicides can lead to the development of weed species that are resistant to these chemicals, making them harder to control in the future.

To minimize the potential health and environmental effects of weedicide use, it is important to use these chemicals responsibly and follow label instructions. Proper use includes wearing protective clothing, avoiding use in windy conditions, and ensuring that the weedicide is only applied to the target area.

In addition, it is important to properly dispose of any leftover chemicals and containers in accordance with local regulations. Finally, consider alternative methods of weed control, such as manual removal, mulching, and crop rotation, to reduce the need for chemical interventions.


In conclusion, weedicides are chemical substances used to control or kill unwanted plants, also known as weeds. They work by disrupting essential metabolic processes in plants, leading to their death. Different types of weedicides have different mechanisms of action, with some inhibiting photosynthesis, disrupting cell division, mimicking or blocking plant hormones or inhibiting specific enzymes.

Selective herbicides target specific plant species while sparing others, while contact herbicides act by direct contact with the plant's foliage, and systemic herbicides are absorbed by the plant and transported to other parts of the plant.

While weedicides can be an effective tool in weed control, it is important to use them judiciously and in accordance with the manufacturer's instructions to minimize their impact on the environment and non-target organisms.


Q1. How long does weedicide last?

Ans. The effectiveness of weedicide can vary depending on the type of product used and the environmental conditions. Some weedicides may provide long-lasting control, while others may need to be reapplied frequently to maintain their effectiveness.

Q2. Can weedicide be used on all types of plants?

Ans. No, weedicide should only be used on plants that are listed on the product label. Using weedicide on plants that are not listed can result in damage or death of the plant. Additionally, some types of weedicides are only effective on certain types of plants, so it's important to choose the right product for the job.

Q3. What are the alternatives to weedicide?

Ans. There are several alternatives to weedicide, including mechanical methods like hand weeding, hoeing, or mowing. Other options include mulching, cover cropping, and using natural weed suppressants like vinegar, corn gluten meal, or clove oil. It's important to choose the right method for the job based on the type of weeds, the location, and the resources available.

Updated on: 14-Apr-2023


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