Category: Weeds

Spring Weed Control

Thanks to our friends at Sod University and Todd Valley Farms for this contribution.

Spring Weed Control: The Effective Use of a Pre-Emergent Herbicide

There is a lot of false data and misinformation surrounding pre-emergent use on lawns.  Pre-emergents, when used properly, can be one of the most effective tools for keeping your yard healthy and weed free. It is important to understand how they work and  what their limitations are before you can truly harness the power of this tool. First, it is important to note the difference between pre-emergent and post-emergent herbicides. A pre-emergent, as its name suggests, prevents the weed from emerging in the first place—this is useful if you are expecting the same kind of weed to appear annually or to control weeds before they appear so that you can reduce labor spent outside hand-pulling them. A post-emergent herbicide kills weeds after they have already appeared—you’ve already spotted them growing in your lawn. Nick Radford of Todd Valley Farms Inc., who discusses the effective use of a pre-emergent as the season for spring pre-emergent applications grows closer.

Contrary to popular myth, pre-emergents do not prevent seeds from germinating. They attack seeds during the germination process. Pre-emergents work by blocking the plant from producing the protein that allows plant cells to divide during mitosis. This cell division is what we see as growth. The initial cell division happens inside the seed coat. If the seed does mature past this stage, the root development will have been damaged, causing the plant to die lacking the ability to properly find or process nutrition. The pre-emergent then also acts as a root pruner. This causes young vulnerable roots to turn inward and stunts their growth.

Photo Credit: www.geckopest.com

The other myth that I often hear is that if you aerate your lawn after applying a pre-emergent, it will make the pre-emergent ineffective. This is also not 100 percent true. It is not something that you should do as it does not help the effectiveness. However, if you must aerate after an application, it will not completely ruin the effects of the pre-emergent. Pre-emergents stay in your soil and create a barrier layer that seeds in this zone are affected by. The soil removed during the aeration process will break apart and fill back into the holes over time or you discard the dirt plugs letting the holes fill back in with remaining soil. In the case of the latter, you have wasted money on the pre-emergent that remained in the soil plugs you discarded.

Photo Credit: www.horizononline.com

Should I use a pre-emergent upon sod installation, seeding or plugging?

Use of a Pre-Emergent Upon Sod Installation or Seeding

There is no reason to use pre-emergent on newly laid sod. If you have taken all the proper steps prior to putting the sod down and thoroughly sprayed out all the pre-existing weeds, there should be few weeds that survive. Those that do survive are easily pulled by hand or controlled with a post-emergent later. It is important to know that the root pruning effect of the pre-emergent is damaging to sod. Some varieties of turfgrass are less susceptible to major damage, but it is not healthy for any variety. When you are seeding a lawn on the other hand, your common pre-emergents will kill the seed that you put down. It is never recommended to use Prodiamine, Dithiopyr, Isobexen or any derivative of these when seeding. It will destroy your lawn 100 percent of the time.

Use of a Pre-Emergent Upon Plugging

When you are plugging a lawn, it is highly recommended to use a pre-emergent. After spending a lot of time on experimenting with different pre-emergents on different types of plugs, I have not found one yet that damages the plugs. In fact, when you plug your lawn without pre-emergents, it takes two to three times longer for the yard to fill in!

I have read many, many university studies on pre-emergent herbicides and researched how pre-emergents work. Based on the studies and the data I found, this should not be the case. The root pruning properties and the effect it has on mitosis should prevent the plug from spreading or maybe living at all. I have a few theories for why this is not true for plugs. The best reason I can give is this: the stolons the plugs spread out obtain enough nutrients from the mother plant to sustain the root development through the layer of pre-emergent. The original plug is mature enough to not be affected by the pre-emergent. Whatever the reason, I have seen no damage to plugs using pre-emergent and the reduction of competition from weeds allows the plugs to fill in at an accelerated rate. Also, warm season grasses can have negative effects when post-emergent weed killers are applied in temperatures over 90 degrees Fahrenheit. For this reason as well, it is better to control the weeds before they become an issue.

When Should Pre-Emergents Be Applied?

Pre-emergents should be applied at least twice a year. They should be applied in the spring before the ground temperature reaches 55 degrees Fahrenheit. Then it should be applied again in the early fall after temperatures begin to come down. The exact dates for this differ depending on the climate zone you live in. It is my personal practice to make three applications a year: March 1st, June 1st and September 1st. A good tip is that it is better to apply it early rather than late. As previously stated, pre-emergents do not kill existing weeds—putting it down after weed seeds have germinated is not effective. Unless it is washed away by heavy rains, pre-emergents will remain dormant in your soil until the soil temperatures rise. So, applications made in the late fall may still be effective the following spring.

When you use it while planting grass plugs, you should put pre-emergent down immediately following the planting of the plugs. I recommend applying it to newly planted plugs every three months until the area has filled in completely. It should not be used if you have overseeded or intend to overseed within six to eight weeks (or sometimes longer depending on the pre-emergent used).

Which Pre-Emergent Should I Use?

There are many types of pre-emergents and many pre-emergents are the same with a different name. The two most common are Prodiamine and Dithiopyr (Dimension 2EW).  These are both good products and they both are easy to find and apply. It is important to know that no single pre-emergent works for all weed types. Prodiamine is less expensive and stays put in your soil longer. Dithiopyr is a little more expensive and can wash through your soil more easily, but it also has post-emergent properties that others do not have. It will kill young weeds up to the three-leaf stage of growth. This makes it a better choice if you are slightly late with your application. Most premixed over the counter pre-emergents have two or more varieties mixed to cover a broader spectrum of weeds. I personally like to use a combination of Prodiamine, Dithiopyr and a small percentage of Isoxaben (linked below). I have found this to be the most effective for the large variety of weeds I encounter.

Fall Weed Control – Now is the time.

Thanks for this from our friends at Sod Solutions.

The heat of summer is slowly coming to an end and the cool temperatures of fall are finally among us. When it comes to the beginning of fall, a lot of people may think that this signifies the end of lawn care. Although time spent outside on your lawn may be greatly reduced, the time that takes place between summer and fall is still important for preparing your lawn for winter and next spring. Applying a pre-emergent herbicide to prevent winter weeds is one of the best things you can do for your lawn during this time.

Certain annual weeds can continue to grow during the winter. These include poa annua, common chickweed, purple deadnettle, and henbit. Certain annual weeds typically emerge in the fall and winter and continue to grow actively in spring. After they flower in spring and disappear during the summer, they often return again in the fall or winter when seeds germinate.

What is a Pre-Emergent Herbicide?

Pre-emergent herbicides, as the name suggests, are a category of herbicides that prevents weeds from appearing in the first place. The difference between a pre-emergent and post-emergent herbicide is a pre-emergent herbicide should be applied before a weed grows while a post-emergent herbicide should be applied if you already have weeds in your lawn. Pre-emergent herbicides form a barrier in the soil that prevents weeds from sprouting or germinating as illustrated in the image below. It can be hard to get rid of weeds once they are already growing in the spring, so get ahead of the game by applying a pre-emergent herbicide in the fall and save yourself time and money—especially if you already know which weeds tend to come around in the spring every year.

Photo Credit: https://www.horizononline.com/when-to-apply-pre-emergent-herbicide/

Apply a Pre-Emergent in the Fall

The best time to apply a pre-emergent herbicide to your lawn is between the months of August and November for both warm and cool season grasses. Your soil temperature should be below 70 degrees and dropping. Be sure to follow up with a second application of a pre-emergent herbicide in the spring before temperatures start to warm up as well.

Selecting a Pre-Emergent Herbicide

When it comes to selecting a pre-emergent herbicide, choices can be daunting. Narrow down the selection process by looking for an herbicide that works on the type of weed you are seeing and for your type of grass. Most herbicides will say on the back of the product which grasses they can and shouldn’t be used on as well as which weeds they will kill. It is important that you choose a selective herbicide. A non-selective herbicide will kill all plants it comes in contact with—including your grass. A selective herbicide will kill only the weeds you want to rid your lawn of. Once you have simplified your choices of herbicides, the last thing to choose between may be a granule vs. a liquid herbicide. Liquid herbicides are usually mixed with water and then sprayed. Granular, or dry herbicides, are small pellets coated with herbicides that can be applied with a push spreader or a hand-held spreader. Either choice of granular or liquid herbicides will perform well on your lawn. The most important thing to look for is that it kills the weeds you have and works with your type of grass.

Maintenance – Weed Control

A weed is a wild plant growing where it is not wanted and in competition with other cultivated plants or grass.  Truth be told, almost all lawns have some weeds. What we are talking about here is weed control—not 100 percent weed elimination.

FOUR WAYS TO REDUCE WEEDS IN YOUR LAWN

1. MAINTAIN A LUSH, HEALTHY LAWN

In order to establish itself in your lawn, a weed needs the same three things your lawn requires: contact with the soil, water, and sunlight.

For this reason, weeds are more likely to sprout up in bare or thin spots of your lawn. Your best defense against weeds is to maintain a healthy, lush, dense canopy of grass that outcompetes a weed’s ability to establish itself. The thicker your lawn’s canopy, the less likely weeds will be capable of growing.

Lawns with open canopies such as St. Augustine grass, or those that are slow to recover from damage (centipede grass, some tall fescues, and bluegrass) expose themselves to weed establishment more than those with thicker canopies (zoysiagrass) or those with more rapid recovery from damage (bermudagrass).

2. CONSIDER MOWING YOUR OWN LAWN

If you pay the neighborhood boy to mow your lawn or hire a professional, keep in mind that your lawn is being mowed with the same equipment that just mowed another type of grass. Therefore, it is very likely dispensing small plantlets of another grass variety into your lawn.

For example, if you have a brand new zoysiagrass lawn and Johnny mows it right after mowing the bermudagrass lawn of Mrs. Smith, then you will probably have bermudagrass in your zoysiagrass before too long. This threat is primarily a concern in warm season lawns that are propagated vegetatively, meaning a fragment of the parent plant reproduces more plants.

3. FREQUENT MOWING & HAND PICKING

The great thing about mowing your lawn (assuming you have a walk behind mower) is that you get to walk every foot of your lawn pretty regularly, allowing you to keep a close eye on the status of any potential weeds.

Mowing a weed before it puts up a seed head will eliminate that weed’s ability to spread seeds and propagate the next generation, so mowing alone can be one form of weed control.

If your lawn has relatively few weeds, you should consider just hand picking them. Be sure to pull out the root if you can. It’s good exercise and its 100 percent organic.

4. USE HERBICIDES

Herbicides can be selective or non-selective. Selective herbicides kill some plants but not others. For example, a selective herbicide might kill dandelions, but it will do so without bringing damage to your lawn.

A non-selective herbicide kills all plants in comes in contact with. Unless you want to kill your lawn to replace it, you will only want to use selective herbicides that specifically state they will not kill your lawn type on the label.

Herbicides control weeds one of two ways: before they germinate or after. A pre-emergent herbicide is used preventatively to keep weeds from popping up in the first place. A post emergent herbicide is used after a weed has already established itself in your lawn.

A Word of Caution for Newly Sodded Lawns:

The sod from sod farms are treated on a regular schedule. If you happen to see a weed while laying the sod, its no big deal. Chances are it has already been treated and is dying but it doesn’t hurt to pull it out while its right there.

A pre-emergent contains a chemical that prevents a weed from putting down roots. As a root inhibitor, it can also negatively affect your newly sodded lawn since it too will be trying to put down roots.

If you successfully killed and removed your old lawn including all the weeds in it, your newly sodded lawn should have relatively few weeds. It is suggested that you hand pick weeds out of your newly sodded lawn for the first season.

Nutsedge

A word about one of the toughest weeds to get rid of and why it shows up in your newly sodded lawn. This discussion has been had many times and after consulting several sod farms, The nutsedge in your newly sodded lawn didn’t come in with the sod. Nutsedge is a plant that reproduces primarily by tubers. When the soil is disturbed either by tilling, digging or raking, you may bring dormant tubers toward the surface where conditions are right for them to grow. If your nutsedge is from tubers and not the nut, it is easier to get under control. Sledgehammer is a brand of herbicide that does very well controlling nutsedge.