Fall is an important time of year for weed control.
Laying down a pre-emergent herbicide at the right time can prevent cool-season weeds from developing over the winter.
But failure to act often means a weed-infested yard from February to April.
Not all pre-emergent herbicides work well against weeds that germinate in the fall. So it’s important to choose one that does.
So in this article, I’ll show you the best fall pre-emergent herbicides. And some of my favorite products that contain them.
Let’s dive in!
The Best Fall Pre-emergent Herbicides
Prodiamine
Prodiamine is one of the longest-lasting pre-emergent herbicides. And it also works out to be one of the most economical as you don’t need to use a lot to get good results.
You can use prodiamine for the pre-emergent control of approximately 30 broadleaf and grassy weed species. Including some of the most common cool-season annual weeds, such as chickweed and henbit. It’s also good at controlling Poa annua.
My Recommended Choice:
The Andersons Barricade Granular Weed Control On Amazon
Dithiopyr
You can use dithiopyr for pre-emergent control of a wide range of annual broadleaf weeds and grassy weeds, including Poa annua.
Professionals often use dithiopyr in commercial settings such as playgrounds, golf courses, roadsides, athletic fields, and industrial sites. But it’s also a top pre-emergent herbicide for established residential lawns.
My Recommended Choice:
Dimension Pre-Emergent Herbicide On Amazon
Isoxaben
Isoxaben is a great choice for controlling winter annual broadleaf weeds. But, it’s not as effective at preventing grassy weeds. So if you’re looking to control Poa annua, you should try a different pre-emergent herbicide.
My Recommended Choice:
Gallery Speciality Herbicide On Amazon
How To Select A Pre-emergent Herbicide For The Fall
There are many different types of pre-emergent herbicides available on the market. But not all of them work equally well on all weeds.
Before making a selection, it’s a good idea to identify the type of weeds that you’re trying to prevent. Then you can choose a product labeled for that use.
You also need to consider your grass type because some herbicides might cause harm. Again, check the label to ensure your product is suitable for your grass.
Once you’ve selected an appropriate product, the final thing to consider is whether you choose liquid or granular. To use a granular pre-emergent, you’ll need either a broadcast or drop spreader. To use a liquid pre-emergent herbicide, you’ll need the best herbicide sprayer.
Preventing Winter Annual Weeds
When temperatures cool in the fall, winter-annual weeds such as chickweed, Poa annua, common mallow, and henbit germinate. Lawns untreated with a pre-emergent herbicide run the risk of being infested with weeds from February to April of the following year.
For effective treatment, you need to know when to apply pre-emergent weed control.
Ideally, you should apply the pre-emergent herbicide to the soil a couple of weeks before germination occurs. Usually, this is some time from mid-August to mid-September.
To judge the right time to apply the pre-emergent herbicide, wait until the soil temperature drops to 70°F. Use a soil thermometer to keep track of the temperature change until the soil has cooled sufficiently.
Alternatively, you can wait until daytime temperatures are in the mid-70s for several days in a row.
It’s often a good idea to apply a second application of pre-emergent herbicide 4-8 weeks after the first one. This makes sure of full weed control until the spring. This second application is particularly important for controlling Poa annua, which has developed a degree of resistance to pre-emergent herbicides.
Can You Use A Pre-emergent To Control Perennial Weeds?
Unfortunately, you can’t use pre-emergent herbicides to kill existing perennial weeds. But you can use it to stop their spread by seed, preventing new plants from developing.
Perennial weeds grow back each year from an existing root system. Pre-emergent herbicides prevent weed seeds from developing after germination. But they don’t have a big affect on plants with established root systems. That’s why you can use a pre-emergent on your lawn without harming the grass.
To control perennial lawn weeds, you need to use a post-emergent weed killer. The fall is a good time to target perennial weeds. As the temperatures cool, the weeds store carbohydrates in their roots. A systemic post-emergent herbicide is easily carried along with the carbohydrates. When the roots die, the weeds can’t regrow.
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