In order to understand how weedkillers work, we first need to understand what a weed is. There are many types of weed and the type you have will determine the weedkiller you choose to get rid of them.
Weeds are the bane of many gardeners’ existence These unwanted plants can quickly take over your nicely manicured lawn or lovingly tended flower beds Getting on top of weeds early is key to maintaining a beautiful outdoor space. But pulling or digging up weeds by hand is exhausting work. That’s where weed killers come in handy. But how exactly do these chemicals get rid of pesky weeds? Let’s take a deeper look at understanding weed control products.
What Defines a Weed?
Before exploring weed killers, it helps to understand what classifies a plant as a weed. The dictionary defines a weed as “a wild plant growing where it is not wanted.” Basically, any plant that pops up where you don’t want it is technically a weed.
Some common garden weeds include
- Dandelions
- Crabgrass
- Creeping Charlie
- Bindweed
- Thistle
- Chickweed
- Oxalis
- Clover
These plants spread aggressively, choking out desired plants in flower beds or invading lawn grass. Their fast growth and tenacious roots make them difficult to control.
Why Use Chemical Weed Killers?
Physically removing weeds through digging, hoeing or hand pulling provides only temporary relief. Weeds like dandelions will quickly regrow from any root fragments left behind. And dealing with extensive weed problems through physical labor alone isn’t practical.
That’s where weed killers offer a useful solution. These chemical products are specifically designed to target common garden weeds. When applied correctly, weed killers provide efficient, long-lasting weed control with much less work compared to manual removal.
How Do Weed Killers Work?
Weed killers contain active ingredients that disrupt normal plant growth. The chemicals interfere with biological processes necessary for plant survival.
Here are some common ways weed killing products damage plants:
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Disrupting cell membranes: Certain ingredients, like pelargonic acid, destroy the wax covering on plant leaves and stems. This allows the plant tissue to dry out.
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Inhibiting photosynthesis: Chemicals like glyphosate block the shikimate pathway, preventing plants from producing proteins needed for growth.
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Mimicking plant hormones: Synthetic auxins cause abnormal, uncontrolled growth leading to the plant’s death.
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Inhibiting amino acid production: Acetolactate synthase inhibitors block amino acid synthesis, starving the plant.
The exact mechanism depends on the active ingredient(s) in the weed killer product. But the end result is the same – plant death.
When to Apply Weed Killers
Timing is important when using chemical weed control. Here are some guidelines on when to apply weed killers:
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Spring or early summer – When weeds are young and actively growing.
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Early fall – To control perennials by hitting them when they transport nutrients to roots before winter dormancy. Avoid late fall application.
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Two days after mowing – Mowing stresses grass so wait 48 hours before applying weed killers.
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Calm weather – Wind can spread chemicals to wanted plants.
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Morning or evening – Avoid midday heat which causes rapid drying and reduces absorption.
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Before rain – Watering in helps with soil penetration.
Following label instructions carefully, including proper timing, is key to getting the best results from weed killing products.
Types of Weed Killers
There are several major categories of weed killers, each with pros and cons:
Selective Weed Killers
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What they do: Kill broadleaf weeds but not harm grasses.
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Common uses: Lawn weed control.
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Examples: 2,4-D, dicamba, MCPP.
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How they work: Synthetic auxins cause susceptible weeds to grow uncontrollably until they die.
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Notes: It takes about 3 weeks to see full effects. Avoid use when temps will exceed 85°F.
Non-Selective Weed Killers
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What they do: Kill all types of plants they contact.
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Common uses: Driveways, patios, gravel paths.
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Examples: Glyphosate, glufosinate, pelargonic acid.
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How they work: Various modes of action depending on active ingredient. Disrupt biological processes.
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Notes: Avoid contact with wanted plants. Fast acting but no residual control.
Pre-Emergent Weed Killers
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What they do: Prevent germination of weed seeds.
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Common uses: Bare ground, driveways, gravel paths.
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Examples: Pendimethalin, prodiamine.
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How they work: Form a barrier that blocks weed seed germination.
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Notes: Apply before weeds sprout. Last 6-8 weeks. Don’t use in planting beds.
Post-Emergent Weed Killers
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What they do: Kill weeds after they’ve sprouted.
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Common uses: Lawns, planting beds.
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Examples: 2,4-D, quinclorac, dicamba.
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How they work: Absorbed through leaves and disrupt growth processes.
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Notes: Most effective on young, actively growing weeds.
How to Apply Weed Killers
There are several techniques for applying weed killers:
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Spot treatment: Spray individual weeds using a handheld or backpack sprayer. Less waste compared to broadcast spraying large areas.
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Broadcast spraying: Use a tank sprayer or spreader sprayer to cover extensive weed infestations. More wasteful so only do spot treatments where possible.
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Wiper applicators: Chemical-soaked sponges or ropes allow targeted application to weeds while avoiding surrounding plants. Useful in ornamental beds.
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Adding to water: Some products are designed to mix into watering cans or sprayers. Good for small jobs.
Always carefully follow label directions for the individual product you’re using. Wear protective clothing to limit exposure when handling weed killing chemicals.
Effective Weed Control Starts with Understanding Weed Killers
While the active ingredients and modes of action differ between products, all chemical weed killers are designed with one goal in mind – destroying unwanted plants. Their efficiency makes them a useful part of an integrated weed management plan.
Understanding the different types of weed killers along with proper application techniques and timing empowers you to harness the power of these chemicals. A thoughtful weed control strategy that combines targeted herbicide use, manual removal, and prevention through mulching and planting densely will help you keep your landscape lush and weed-free.
What is a weed?
The dictionary says that a weed is ‘A wild (not deliberately cultivated) plant growing where it is not wanted.’ By this definition, virtually any plant that’s growing where we don’t want it to grow is a weed.
But it’s those unwanted plants that invade and threaten to take over your paths, patios, flower beds, borders and lawns that are the real problem. If you need any help identifying plants that are commonly thought of as weeds, we have recently written an article showing the characteristics for identifying weeds.
Weeds can be very frustrating and extremely difficult to remove, especially without them reappearing. With traditional methods of weed removal proving to be very arduous work in some circumstances there needed to be a more effective alternative.
Weedkillers are chemical-based liquids that are specifically engineered to target different types of weed in the best way possible. Whatever the weeding job that you are trying to tackle, there is a weedkiller that is matched to that job and will do exactly what you need.
When to use weedkillers
Weeds can generally be killed at any time of the year. But the best time to use weedkillers is when they are growing strongly (usually in the Spring and Autumn) because they absorb weedkiller more quickly. This is particularly the case with Systemic and Selective weedkillers which rely on activity within the plant for their effectiveness. Apply liquid weedkillers in calm conditions to minimise the drift of the solution onto wanted plants. Application to the leaves results in weedkiller moving up to the growing points and down to the root tips.
Location of the weed is also important. For example, if a weed is growing in the middle of the lawn then you should use a selective weedkiller, and if it is growing between patios or pavings then a residual weedkiller would be more appropriate.
In situations when you are looking to clear a patch of land and plant up quickly it is possible to use a glyphosate-based weedkiller which would allow you place new plants after only 24 hours without causing the new plants any harm.
How Roundup Kills Weeds (And How Weeds are Fighting Back)
FAQ
How does a weed killer know what to kill?
Selective weed killers contains auxins, which are absorbed by the weeds than the desired plants; making the weeds to grow abnormally or die out; ahead of beneficial plants.
How long does it take for weed killer to work?
Most weed killers start working within a few days, but complete weed death can take anywhere from a week to several weeks, depending on the type of herbicide, the type of weed, and environmental conditions. Contact herbicides, which kill on contact, can show results within hours to a few days.
What happens after you spray weed killer?
When the weeds have been sprayed, it can take a couple of days for the chemicals to be drawn down into the root of the plant. There are a few different variables that affect how long you should wait before attempting to pull up the weeds: How strong was the weedkiller? Weaker formulas take longer to work.
How does weed killer kill weeds but not grass?
Weed killers, also known as herbicides, can selectively target weeds while leaving grass unharmed because they exploit differences in plant biology. These differences can be in metabolism, growth patterns, or specific enzymes.