Pre-emergent herbicides: what are they? | Greg Carrick, Garden City Plastics

What’s the one thing in any garden that, after all your best efforts, still causes major issues and major headaches? …. Weeds.

Simply put, a weed is a plant growing in the wrong spot. On their own, not hard to remove. As a group, time consuming and costly to manage whether it be a domestic situation or broader landscape area such as parks and sporting fields because they grow, seed and spread quickly.

In public spaces, weed-infested gardens and landscapes are unattractive and at worst create wastelands that the public avoid. On the flip side, well-managed landscapes are a haven for community activity. By doing all we can to enhance these spaces, we can play a significant role in enhancing the health of the local population.

So, what’s a solution?

Effective Herbicide use.

You can cover a wide area in a short time and control what’s there. This approach is the most commonly used with what’s defined as NonSelective Post-Emergent Herbicides. Some of the most common are:

• Round-Up (Glyphosate) - a Systemic herbicide meaning it is absorbed and runs through the veins of the weed and effectively stops the roots absorbing moisture.

• Basta (Glufosinate Ammonium) and Slasher (Pelargonic Acid) - contact herbicides which means they will generally kill the cells of the part of the plant that it hits.

Currently, post-emergent herbicides dominate management processes to controls all weeds and some grasses in one pass. The problem this poses is that once a weed has entered an area and established itself, greater resources are required to control its spread and reduce its impact.

Often, subsequent applications are required to get on top of the infestation once the weeds germinate again. This usually involves manual labour which is a time-consuming and costly option.

Then what’s a better solution?

Pre-emergent herbicides.

An innovative approach that effectively deals with weeds, while also reducing the associated costs, Pre-Emergent Herbicides are a way of treating weed free soil to prevent the weed seeds growing back for a period. They’ll inhibit the growth of small, germinated weeds and stop them before they become a visual issue.

Science shows this preventative approach can disrupt weed seed germination for up to 6 months.

The effectiveness of a Post-Emergent Herbicide can be amplified by an application with a Pre-Emergent Herbicide as the second method will cut the number of seeds that will attempt to germinate in future months.

Essentially, Pre-Emergents can be applied once per season, rather than needing to apply a post-emergent monthly or bi-monthly. This saves you significant time, labour and expense without compromising on the quality of your greenspace.

A number of Pre-Emergent Herbicides are available:

Barricade (Prodiamine) - can be applied directly over the plants in most situations by spraying over garden beds or turf, with no harm to what’s growing.

After spraying you can lightly water the Barricade into the soil or wait for a light rain event to wash it into soil where it binds with soil particles to create the barrier against weeds.

Round-Up would typically be used to reduce weeds, then followed with an application of Barricade that would significantly reduce the number of weeds germinating. Depending on the situation control is around 90%+.

The one application significantly reduces the need to return to the site on a monthly basis to conduct another application of the glyphosate. Sierraron 4G - a granular option distributed with an applicator/spreader over the area. Again watered in, the active ingredient binds strongly to the soil, minimising the potential for run-off or leaching. So long as soil is present Sierraron G goes to work after watering in and it eliminates most annual and perennial broadleaf weeds and grasses for up to 6 months.

Where are the best areas to use Pre-Emergent Herbicides?

• Garden Beds around plants

• Gravel driveways and paths.

• Fence lines, tennis courts, etc

• Around the base of trees in parks

• Driveways

You’ll know after using either the liquid or granule option where they are best suited in your specific situation and location.

In the spring as the ground heats up and weeds begin to germinate, the weeds will hit the preemergent barrier in the soil and die. Essentially, the pre-emergent is killing the weed while it is still underground, before it can fully grow and appear in your lawn area, garden bed or turf area. In summary, the use of a Pre-Emergent Herbicide can:

• Reduce the reliance on post-emergent sprays

• Reduce the visits to the garden for weed control in general

• Help maximise the growth of the plants you want to grow, not the one you don’t!!

After you have mastered the application of the Pre-Emergent Herbicides, your gardens will be less work, easier to maintain and better looking over the long term, delivering a beautiful landscape for all to enjoy.