How To Prevent Weeds In Your Lawn with a pre emergent herbicide

Written by Ian Thompson

Ian holds a Masters in Turf Management from Sydney University, has over 20 years experience working as a golf course Superintendent, turf manager, product formulation and development. We call him our resident Lawn genius.

Having weeds in your lawn is an unsightly affair, they compete for nutrients and water and they are very very good at it, some even grow faster than your lawn meaning you need to get out there and mow more often then you should be.

Weeds are very adaptable, not only do they compete with your plant but they also have some very cool (but annoying) features that make them hard to destroy. Weeds like Clover pull nitrogen out of the air to grow faster than your lawn, Oxalis has huge amount of bulbs allowing it to come back, again and again and again.

So being born from turf professionals we are very passionate about keeping our lawns weed free and the best way to do that is not to kill them but to prevent them ever stepping foot on our lawns.


Herbicides (the things that kill weeds)

Understanding the types of herbicides that exist is probably a good place to start. There are 3 distinct herbicide groups that you need to understand:

Total herbicides- These kill nearly everything they touch and some things they don’t these aren’t for your lawn.

Post-emergent herbicides- as the title suggest, these herbicides are for post (after) the weeds have emerged. This is just a broad title are there are even sub-groups among these.

Pre-emergent herbicides- again it’s as simple as pre (before) the weeds have emerged.


All these herbicides have their benefits, but here are some of the reasons we prefer to use pre-emergent vs post-emergent:

Weeds do not emerge from the soil

Weeds are not able to produce new seeds

With no weeds mowing is reduced

Reduced competition with lawn for nutrients and water

Improved, consistent surface for ball sports

Reduced risk of damage from the application of post emergent herbicides



So how does it work?

While Pre-emergent herbicides are a relatively new concept to many home owners, they have been around for a long time, in fact they were first discovered when a clothing dye was spilt outside a factory and weed suppressing properties were noticed, enter the Dinitroanalines group of pre-emergents, still in use today.


Different groups of pre-emergents work in different ways, one of the most commonly used pre-emergent in professional turf and our recommendation is Barricade. It works by persisting in the top portion of the soil for up to 6 months (so prevents for up to 6 months). Here it forms a barrier (a barricade if you will…) around the edges of the weed seed, so as the seed attempts to put down it’s first root the herbicide impedes the development. It strongly binds with organic matter in the soil so doesn’t disappear with normal rainfall.


Why do we recommend it over other products?

Prodiamine, the active is Barricade has been proven in the professional sector, so we know it works and works well. It lasts for up to 6 months, so it’s as simple as 2 applications. It is exempt from poison scheduling and as an added bonus it can be used for your ornamental gardens as well as your lawn.


How to use the product?

It is a professional product so it’s recommended that you read this in detail before making an application, if you have any questions please feel free to ask the Lawn Genius. At the end of the day it really is as simple as applying it to your lawn and watering in.


Applying the product

Measuring your lawn

Measuring your lawn to ensure the right amount of product is applied is a critical step. 

We do love a “Genius Tip” at The Lawn Shed, so don’t run out with your tape measure and try to do try to remember who that Pythagoras guy was. Google Earth is a great tool for measuring your lawn and garden areas (you will need Google Chrome or to download the app).

Simply zoom into your lawn, click on the ruler tool on the left and then click little dots around the edge of your lawn. Once you’ve gone all the way around double click the original dot and you’ve got your lawn size. The more you zoom in, the more accurate you can be.  


Choosing a rate

The label has a few different rates, because different types of weeds require more active ingredient to suppress the seeds growth.

For the lawn the label rates start at 10ml per 100m2 and run up to 40ml per 100m2 for more difficult to control weeds. In the garden these jump up a bit to 40-80ml per 100m2.

It’s as simple as identifying the weeds you want to prevent and selecting that rate.


Post application

Barricade is a herbicide that works in the soil so we need to get it off the leaf.  It requires watering in after application, now we recommend doing it straight after application but you do have 7 days to get this done.

The flow and pressure of water mains varies around the country, then you need to allow for different sprinkler types. So, we can’t give you a generic direction on watering for a certain amount of time. The recommended water amount is 6mm of irrigation not 6mls, so how do you measure this? Well, you could easily use an empty can (Tuna is one of our favourites) to measure the water being applied. Once the can has filled up with 6mm of water then it’s been watered in sufficiently.


So hopefully that has helped you with understanding what a pre-emergent is and the benefits you can see from applying them to your lawn. Now remember if you have any other questions, feel free to ask the Lawn Genius.



Frequently Asked Questions

How does a pre-emergent work?

They all work slightly differently, however Barricade herbicide forms a barrier around the weed seed, so as the seed attempts to put down it’s first root the herbicide impedes the development. It strongly binds with organic matter in the soil so doesn’t disappear with normal rainfall.


What is the best one for my lawn?

We recommend Barricade herbicide, being exempt from poison scheduling it’s more suitable for the home owner and their equipment. Prodiamine, the active is Barricade has been proven in the professional sector, so we know it works and works well. It lasts for 6 months, so it’s as simple as 2 applications.


What weeds does it prevent?

One of the advantages of Barricade herbicide is it is very effective against weeds that are hard to control from a post-emergent point of view. Weeds like Oxalis, paspalum, crabgrass, crowsfoo, wintergrass, summer grass and many others.


Can I apply it in my garden bed?

Yes, it can be applied to prevent weeds in your ornamental garden bed but it is recommended that it is applied below fresh mulch. It is not suitable for any gardens that contain edible plants.


What lawns can Barricade herbicide be applied to?

Barricade herbicide is suitable for most common home lawns including Kikuyu, Buffalo, common and hybrid couch varieties and Blue couch.


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