When weeds invade your yard, it can be difficult to get rid of them. You can spray the weeds until they’re gone. But if they’ve already spread their seeds, they’ll reappear next year in even greater numbers.
To reduce the amount of work each year, it’s a good idea to use a pre-emergent herbicide. This stops the weed seeds from developing and sprouting.
Choosing the right chemical for your weed problem is a large part of the battle. So I’ve prepared this pre-emergent herbicide list to give you further guidance.
Let’s take a closer look.
Are you looking to prevent annual grassy weeds such as barnyard grass, crabgrass, and foxtail?
But do you still want other cool-season lawn plants to grow?
If so, siduron is the pre-emergent to get. But it’s not for use on bermuda grass or some types of bentgrass. And it’s not effective on broadleaf weeds such as dandelions.
Trifluralin is a general use pre-emergent herbicide that you can use to prevent broadleaf weeds and grassy weeds. It’s often used by homeowners in garden beds. As well as in agriculture to keep weeds away from vegetables, soybeans, fruits, cotton, and nut crops. But it’s not good for use on lawns.
You’ll find trifluralin in the well-known brand ‘Preen’.
Benefin is a good choice for controlling annual grasses, clover, and alfalfa. As well as some vegetables, such as wild lettuce. But it’s not a good choice for controlling broadleaf weeds.
One drawback of benefin is that it breaks down quickly. And sometimes you need to apply a second treatment a few months later to get the job done. You can also get benefin together with trifluralin so that you can prevent a wider range of weeds.
Isoxaben is good for controlling annual broadleaf weeds such as bittercress, henbit, and chickweed. It’s also good against common perennial weeds such as white clover, dandelions, and plantain. But this pre-emergent herbicide is not very effective at preventing grassy weeds. So if you’re looking for a crabgrass killer, look elsewhere.
Be aware that you’ll have to wait at least two months after applying isoxaben before you can reseed your lawn.
Dithiopyr is good for controlling summer annual grasses. It’s also good for preventing grassy weeds such as crabgrass and goosegrass from growing in your lawn. And if you don’t apply the pre-emergent early enough to stop the seeds from sprouting, you can also use dithiopyr for early post-emergent control of crabgrass.
It also works against a range of broadleaf weeds, but it’s not as effective against them. And you’ll often have to use a higher concentration to get the job done.
Dithiopyr is found in the popular ‘Dimension’ brand.
Pendimethalin is good for controlling annual grasses, grassy weeds such as crabgrass, and broadleaf weeds.
But the long wait time of 4 months or more makes it a bad choice if you want to reseed your lawn soon.
Pendimethalin is often used in agriculture where it’s used to control weeds in fields growing tobacco, potatoes, soybean, cotton, and corn. You can use it both as a pre-emergent herbicide and early post-emergent weed killer.
You can use prodiamine to control around 30 different types of grassy and broadleaf weeds. Including common lawn weeds such as plantain and dandelions. And the difficult crabgrass and annual bluegrass (Poa annua), well-known for their prolific seed production.
You’ll find prodiamine in the popular Andersons barricade granular pre-emergent herbicide.
The Benefits of Pre-Emergent Herbicides
Many gardeners have the experience of killing weeds with a post-emergent herbicide one year, and then watching in horror as the weeds return in the next growing season.
To stop this continuous cycle of annual weeds reappearing, despite your best efforts to kill them, you need to use a pre-emergent herbicide. This works by creating a chemical barrier in the soil that prevents germinated weed seeds from fully developing.
The best time to apply the pre-emergent depends on the weed type you want to prevent. Use them in the spring for summer annual weeds. And again in the fall for winter annual weeds.
The most obvious benefit is that it saves you a lot of time and effort in the future. By applying pre-emergent herbicide at the right times of the year, you can minimize the number of weeds that appear in your garden. Leaving you with occasional spot treatment to keep your yard weed-free.
By repeating the treatment each year you also reduce the number of applications needed in subsequent years. Not only will it prevent weeds from growing to maturity and dispersing seed. But the viable seeds left in the soil will also decrease over time. So the job gets easier with each passing year.
What month do you put down pre-emergent?
To prevent summer annual weeds you need to put down pre-emergent in the spring, usually in March or April. To prevent winter annual weeds you need to apply the pre-emergent herbicide sometime between late summer and early fall. For the best results, make the application a couple of weeks before the weed seeds germinate.
Will heavy rain wash away pre-emergent?
Pre-emergent herbicides need water for activation and to soak into the soil. So it’s a good idea to apply them before rainfall. But heavy rain can wash away the pre-emergent or dilute it and reduce its effectiveness.
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