Your Basic Weed Killer Options

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Herbicides are a very polarising topic amongst gardeners: it seems that we either love them unconditionally, or we have built up some sort of nightmarish fantasy

There are two types of weed killers: selective herbicides, which target certain types of plants, and non-selective herbicides that kill plants indiscriminately. This doesn’t mean that selective pesticides kill only weeds and leave plants that you want to live. Instead, certain plants will be affected by the chemical differently due to their genetic make-up; some will be able to tolerate it, and others will die.

The term “weed” is one of convenience that humans use to distinguish between desirable and undesirable plants. In reality, plants are all equal but play different roles in the ecosystem and have their own preferences, just like us.

Weeds can be very beneficial to the health of your garden by bringing in a greater diversity of beneficial microbiology and insects. They can improve soil structure, and many of them are edible. Before you decide to remove them, ask yourself first if you can learn to love them.

If you’ve decided they really do have to go, the first stop for non-selective herbicides is a product that uses glyphosate (like Monstanto’s Round-Up). Every gardener knows glypho, whether they use it or not. It is the most widely used herbicide globally and is an incredibly useful tool in a gardener’s belt.

Always measure your mixtures based on the label, and this goes for any herbicide, pesticide, fungicide or fertiliser that you use. Mixed at the correct rate, glypho will kill just about any herbaceous plant (that doesn’t have a bulb or rhizome), and many woody plants too.

How Do I Apply Glyphosate?

Glypho isn’t taken up in significant amounts through the roots or trunk without a fresh wound, so don’t worry if your spray touches the base of a desirable tree, it should affect a plant only if it touches the leaves. Any leaves sprayed that you don’t want to die should be immediately removed either with your fingers or a pair of cutters. Avoid getting glypho on the fresh wound you’ve just made, which is even worse than getting it on the leaves.

You can “carpet spray” any areas that you want to kill with a backpack or handheld spray pack, or paint onto leaves with a paint brush to be more discriminate in your killing. Check the weather forecast, because if you have rain forecasted later the same day as spraying it’s likely that the chemical will be washed off.

Some woody plants need extra attention, like drilling into the roots or cutting a large tree down and applying straight glypho to the stump. Be quick when applying chemical to the wound of a plant, because they will seal themselves off very quickly with a kind of defensive scab. You want to get your chemical into the vascular system, whether that’s through the stomata in the leaves or through a fresh wound.

How Long Does Glyphosate Take To Work?

Depending on a range of factors including the season, humidity and soil moisture, it takes anywhere from a few days to a few weeks to show signs of working, depending on how fast the vascular system is moving liquids around. Heat and recent rain speed the process up, whereas cold and dry weather slows it down. Signs that the poison has worked are wilting and yellowing of leaves, followed by total browning off and a collapse of herbaceous plants.

This is what weeds that have been sprayed by glyphosate 2-4 weeks ago look like. They’ve gone limp and their leaves are yellowing, and you could just whippersnip them now if you’d like. Photo via Plants Grow Here.

This is what weeds that have been sprayed by glyphosate 2-4 weeks ago look like. They’ve gone limp and their leaves are yellowing, and you could just whippersnip them now if you’d like. Photo via Plants Grow Here.

Is Glyphosate Safe?

Some say that glyphosate is unsafe for humans, however this is up for debate. There are ongoing court cases against Monsanto, the creator of the world’s most famous glyphosate product, Round-Up.

I’m not a doctor, so if you have serious concerns you should do further research or reach out to a medical professional for advice.

According to the American Council on Science and Health, short term exposure to glyphosate is less toxic than table salt.

Long-term exposure is what everybody is really worried about, however long-term studies on rats either show no risk or are inconclusive. The ACSH also state that the European Food Safety Authority looked at 21 studies with humans and found no evidence of danger, and the International Agency for Research on Cancer looked at 19 human trials and found only 3 studies that showed a weak link with non Hodgkin lymphoma.

It’s important to be realistic with our expectations when we talk about carcinogens. According to the World Health Organisation, red meat is also a carcinogen. Both red meat and glyphosate are in the same carcinogenic class 2A, “probably carcinogenic to humans”. So glypho may be harmful, but you’re not going to suddenly drop dead if you accidentally touch it with your bare skin.

Most of us really don’t want to give up using our beloved glypho if we don’t have to, because it’s such an awesome way to get rid of unwanted weeds without dedicating large amounts of time hand-weeding.

Non-Selective Heavy Duty Chemicals

For some woody weeds, like blackberry and ivy, glypho may or may not work. If you’ve waited a few weeks and your weeds still aren’t showing any signs of dying it may be time to bring in the big guns.

Most of the options for hard-to-kill weeds are way more toxic than glypho and should be used with caution including the use of rubber gloves, long sleeves, pants and a face mask.

Blackberries are delicious, but they’re no joke.    Image source

Blackberries are delicious, but they’re no joke. Image source

A “blackberry and tree” herbicide should be heavy-duty enough to get the job done, but then you still have to remove the thorned branches of the blackberry bush…

Selective Herbicides

There are a range of selective herbicides that can kill some weeds and not others. It would be impossible to list them all, but here are three of my favourites to use if I have to, even though I actually prefer not to use herbicides at all.

Dicamba is a selective herbicide that targets dicots and doesn’t hurt monocots. This is another great option for lawns but be careful because you don’t want to accidentally spray that on any shrubs or trees in the garden because they too are probably dicots!

Fusilade is a herbicide that kills grasses and leaves dicots. It’s very expensive but may be worth it when compared to the cost in man-hours to remove grasses from a line of hedges.

“Weed & Feed” is an option that works for selectively killing weeds in your lawn (if you’re into that). It kills most plants considered weeds, even certain clumping grasses while feeding the lawn with essential nutrients. Again, avoid spraying any plants except for lawn and plants you want to kill.

Natural Herbicides

There are more natural alternatives to glypho, but I’ve never found one as effective. One product that does seem to work okay as a non-selective killer is Slasher, though it is much more expensive than glypho and needs to be applied at a far higher rate of mixture.

For this reason, it isn’t economically viable for most commercial operations but may be worth it if you are just looking after your own property and are happy to splash out a bit extra.

Some people recommend vinegar, but I’ve never found it to work. It often just kills the leaves and stems but leaves the roots to sprout up another day.

Conclusion

These are simply some of your basic options when it comes to herbicides that you are likely to use as a gardener, however, this is by no means an exhaustive list.

It would be nice if there was a selective herbicide that targeted any plant we held in our imagination, but alas, no such product exists (unless you count your fingers which can pull weeds by the roots). We have to work with the biological systems that they have evolved, and the chemicals that nature produces, and humans adapt.

Always read the label. Seriously. You need to know if your chemical is going to affect wildlife, waterways or yourself. The last thing you want is to leave a trail of destruction on the ecosystem or your own body just for the sake of some silly war you have against a plant. Also, you need to know what rate to make up the mixture, and if a wetting agent needs to be added to make the chemical stick to and penetrate the plant.

Every chemical is going to have some impact on the soil and microbiological life in your garden, unfortunately. This is the price you pay for convenience. Pulling weeds by hand is the best way to avoid damaging the environment too much. Unless you have a large property and lack time, it’s usually best to just pull weeds by hand to save the beneficial critters we share the land with, or even better, learn to love them and allow weeds to flourish in your lawn.

Look at the intricate little clover inflorescence made up of individual pea flowers.   Image source

Look at the intricate little clover inflorescence made up of individual pea flowers. Image source

Have you ever asked yourself if you can just learn to love your weeds? Not only can they provide food and housing for beneficial organisms, but many are edible and delicious, such as clovers which even fertilise the soil with nitrogen.

Where To From Here?

Now that you know about your basic herbicide options, I recommend another blog I’ve written discussing what “weeds” actually are, and a defence for their existence. I think it’s a helpful accompaniment to this article to really understand weeds and their purpose. Alternatively, try one of the following articles instead.

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