As a homeowner or gardener, you’ve likely encountered the nuisance of weeds invading your lawn, flowerbeds, or vegetable garden. While manually pulling weeds is an option, it’s back-breaking work that rarely eliminates the problem long-term. That’s where weed killers come in handy – but how exactly do these chemical products get rid of weeds? Understanding the science behind different weed killing methods can help you choose the most effective options and use them properly.
Main Types of Weed Killers
Weed killers also called herbicides are classified in different ways based on how they work
Selective vs. Non-Selective
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Selective herbicides target specific weeds but leave desirable grass and plants unharmed Common in agriculture
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Non-selective herbicides indiscriminately kill all plant life they contact. Used to clear areas of any vegetation.
Contact vs. Systemic
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Contact herbicides kill only the parts of the weed they directly touch. Effective on annual weeds.
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Systemic herbicides are absorbed by the plant and translocate to roots and shoots. Best for perennials.
Pre-Emergent vs. Post-Emergent
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Pre-emergent herbicides create a barrier to prevent weed seeds from germinating. Won’t affect existing weeds.
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Post-emergent herbicides target weeds after they’ve already germinated and emerged.
How Contact Weed Killers Work
Contact weed killers like diquat and glufosinate work by immediately penetrating the leaves and plant tissues they touch. Within hours, the chemicals disrupt cellular functions, causing rapid dehydration and plant death.
Advantages of contact herbicides:
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Fast acting – visible effects in hours or days
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Minimal soil residual activity – breakdown quickly
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Useful for burndown of annual weeds before planting crops
Limitations include short-lived effects, requiring repeat applications. Contact weed killers also provide no root kill of perennials.
How Systemic Weed Killers Work
Systemic herbicides like glyphosate (Roundup) are absorbed by the leaves and transported through the plant’s vascular system down to the roots.
The chemicals accumulate in actively growing tissues and disrupt enzyme function, resulting in slow death over days or weeks.
Benefits of systemic weed killers:
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Provide root kill of tough perennials like dandelions
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Maintain weed control for weeks or months
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Can be applied to specific weeds vs. entire area
Drawbacks are slower action than contact weed killers and potential leaching into soil. Systemics may also kill or injure desirable plants inadvertently contacted.
How Pre-Emergent Weed Killers Work
Pre-emergent herbicides like dithiopyr create an invisible chemical barrier that prevents weed seeds in soil from germinating and emerging.
They work by inhibiting processes vital for plant growth. Weed seeds may sprout initially but then wither away.
Advantages of pre-emergent weed killers:
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Proactively stop weeds from infesting an area
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Reduce need for post-emergent weed control later
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Useful in vegetable gardens, flower beds, under trees
Limitations are they don’t impact existing weeds. Reapplication is needed every few months as the barrier breaks down. Care must be taken with timing and placement to avoid impacting intended plants.
How to Use Weed Killers Effectively
Now that you understand how various weed killers work, some tips for effective use:
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Accurately identify weed types to select the best control method.
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For systemic weed control, apply when weeds are actively growing. Avoid mowing prior.
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Time pre-emergent weed killer application for early in the growing season.
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Spot treat individual weeds rather than blanket spraying entire areas.
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Use selective herbicides like 2,4-D near desirable grass and garden plants.
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Combine different types of weed killers for comprehensive control.
Learning the science behind weed killers will ensure you choose the right ones for your situation and use them in the optimal manner. A strategic weed control plan will keep your landscape looking great all season long.
Organic or contact herbicides? Choose the right spraying for weed killers!
Organic herbicides that act on the leaves and stems of the plants to be treated are the best. The effects of spraying appear after just one week. On the other hand, herbicides that are absorbed by weed roots are not as recommended. The first effects take about 2 weeks to see. Furthermore, these chemicals stay in the soil for a very long time, making it almost impossible to clean them up. This can unfortunately have a negative impact on future cultivation at this location.
Call herbicides only kill the parts of the weed that are touching each other when they are sprayed. These agents are very effective if the spraying is thoroughly covered with weeds. If that is the case, weed killing can happen very quickly and last a much longer time. You can learn more about how long weed killer lasts here.
Weed killers break down when they come in contact with soil, so you need to be more precise when you spray them and use better sprayers. These sprayers are also not as accurate and long-lasting as system herbicides. Another good thing about them is that you can see the first effects just a few hours after spraying. Learn more about how weed killer works here.
Our weed killer is also used to destroy unwanted plants on sidewalks, driveways, or paths. It controls individual plants with great precision.
The need to optimize agricultural yields has always driven humans to use chemicals. The use of herbicides has very quickly become established in current crop and garden practices. In the case of a single, widespread application, plants develop resistance to the herbicide over time. This is resulting in a loss of efficacy of the herbicide as it’s an accustoming phenomenon.
How Roundup Kills Weeds (And How Weeds are Fighting Back)
FAQ
How does a weed killer know not to kill grass?
How long does it take for the weed killer to work?
How do most weed killers work?
What happens after you spray weed killer?
How do weed killers work?
To do this, system weed kills are sprayed on the living weed. Then, the herbicide moves throughout the weed internally and travels to the root level, eventually killing it. A selective weed killer may be the best choice if you want to kill weeds that live among greenery you want to maintain..
How do residual weedkillers work?
Residual weedkillers work by creating a weedkilling barrier in the ground that prevents weed seeds germinating. This prevents the weeds from getting established in the first place. They are held on the surface for several months and so control weed growth for a long time.
How do selective weedkillers work?
Selective weedkillers work by stimulating growth in the weed that cannot be sustained. In effect, the weed actually ‘grows itself to death’. They take some time to work – possibly up to 4 to 6 weeks – slower when it is cold, quicker in good growing conditions, warm, moist soil and when weeds are growing actively.
How do non-selective weed killers work?
This works by targeting specific types of weeds, such as dandelions, without harming the grass around the weeds. If you are looking to start from scratch, non-selective weed killers are herbicides that kill or severely damage everything it comes into contact with, unlike contact weed killers.
How long does it take weedkillers to work?
Repetitive doses may need to be applied to fully kill the weed population. Usually, contact herbicides are classified as non-selective. Contact weedkillers work on contact with the leaves of the plant. They start to work as soon as they are applied to the plant. After as little as 10 minutes, some treatments are impervious to rain.
How do herbicides kill weeds?
Systemic herbicides enter the plant through the roots and leaves, and move throughout the inside of the plant. Contact herbicides kill lawn weeds from the outside in. They attack the exposed parts of the plant, killing the weed by reducing its ability to feed itself through photosynthesis.