Everything You Need To Know About Pre-Emergent
Herbicides are used to control and kill weeds in your lawn and garden beds, and pre-emergent herbicides are designed specifically to target weeds before they even show up on your property. As the name suggests, pre-emergent prevents weeds from emerging, which is always the most effective form of weed control.
How Do Pre-Emergents Work?
While this type of weed control will not be effective against emerged weeds, pre-emergents will make sure no new weeds sprout in your yard by preventing seedlings from fully germinating. Pre-emergents do not directly attack seeds or prevent germination in the soil; rather, they create a protective herbicide barrier that sits atop the soil in your yard. As a young seedling tries to push up through the soil, it will hit this barrier and be unable to grow.
Seedlings that are not able to sprout and develop will not be able to develop a root system or absorb nutrients. With no access to nutrition or sunlight, the seedlings will be forced to go into dormancy, or they will simply die. Preventing new weeds from emerging also means you are preventing all those potential weeds from spreading hundreds of more seeds, making pre-emergent weed control a twofold remedy.
Types Of Pre-Emergents
Pre-emergents in liquid form are best for covering a larger area. Many people prefer the liquid types because they provide an even distribution at a fast rate. However, liquid pre-emergents will need to be mixed together, and the spray nozzles they require will have to be adjusted properly, or else you could end up damaging your desired vegetation.
These pre-emergents come in textured granules that can either be dispersed by a feeder or by hand. Granular pre-emergents are best suited for smaller areas, and they have the benefit of needing little-to-no mixing, unlike liquid forms. Granular types must be watered after application in order to break down the pellets and create an effective herbicide barrier.
What Is In Pre-Emergent?
If you see this chemical on a pre-emergent label, you will be well-equipped in the fight against crabgrass and dandelions. Prodiamine is also commonly used to eliminate invasive grasses.
This chemical is often used on larger fields of crops, but it can provide benefits for residential properties. Yellow foxtail and bindweed/morning glory are frequently targeted by this compound.
Like many other herbicides, pre-emergents with this chemical are highly effective against grassy weeds, like crabgrass and creeping bentgrass, as well as many vining weeds and plants.
When To Apply Pre-Emergent
- Spring – Crabgrass, goosegrass, spurge, and many more summer annuals germinate in spring in order to wreak havoc all summer long. To prevent these types of weeds, pre-emergent should be applied in early spring, typically sometime in March. Read more information about common weeds in Illinois here.
- Fall – Annual bluegrass, chickweed, speedwell, and many more weeds are considered winter annuals. These weeds germinate in fall and die in spring, but many will set seeds that go dormant in the soil over winter. Pre-emergent should be applied in late summer or early fall to prevent winter annuals (generally, before mid-September). Be sure to check out other ways to treat common Illinois lawn weeds.
- While Fertilizing – Pre-emergent herbicides are often blended together with fertilizers. Especially when applying an early spring fertilizer, including pre-emergent in the mixture will help ensure that your desired turfgrass is able to grow freely and absorb the maximum amount of nutrition. See our fertilization and weed control page for a deeper look into our programs.
- Before Weeds Are Visible – As previously stated, pre-emergent is only effective on weeds that have not broken through the soil. Applying pre-emergent to visible weeds will not kill them, and it will likely not even harm the weeds. Getting to a baby seedling before it emerges is the best way to control it.
- After Grass Has Grown – The pre-emergent herbicide you decide to use will not be able to differentiate between weed seeds and healthy grass seeds. For this reason, you should never apply pre-emergent directly before or after overseeding your lawn. Pre-emergent will prevent grass from emerging in the same way it prevents weeds. If you plan to lay down seed this fall, make sure you wait until the grass emerges before applying pre-emergent.
While many people enjoy the benefits of applying pre-emergent at the same time as fertilizer, you can always purchase pre-emergent separately. Make sure to check the labels of any fertilizers you purchase; the presence of pre-emergent will be clearly marked on the label.
Perennial and biennial weeds produce seeds that germinate virtually all year long. Pre-emergents will provide that chemical barrier to prevent these types of weeds from emerging, but new seedlings of perennials emerge so frequently that it is almost impossible to fully control them with pre-emergent treatments alone.
Generally speaking, pre-emergents are effective for 3-5 months. Environmental and other factors can alter this time frame, including excessive foot traffic on the lawn, heavy rainfall, or improper fertilization. For the longest-lasting results, wait until the ground temperature is around 55 degrees for summer weeds and 70 degrees for winter weeds, limit activity on the lawn, and make sure to water thoroughly and maintain your yard.
The most important thing to remember when it comes to the proper amount of pre-emergent is that full coverage is your goal. Neglecting even the tiniest area of your lawn or garden beds could easily lead to a weed invasion. A good rule of thumb is that 1,000 square feet will typically need between 1 and 2 gallons of pre-emergent mixture.
For a variety of reasons, you will need to reapply pre-emergent throughout the season. Weed seeds can be dormant in the soil for years, and some weeds can grow without the use of seeds at all, instead using small pieces of stems or roots from which they can regenerate. Weed control is a continuous job, but remaining vigilant and utilizing pre-emergents will keep your property as weed free as possible!