When to use pre emergent weed control?

Contents

When To Apply Pre-Emergent Herbicide

Pre-emergent herbicide is an important tool in an effective weed management program, but properly timing the application can be tricky. In this article, we’ll look at key principles in developing a weed control strategy, what pre-emergent herbicide can and cannot accomplish within a management program, and when to apply pre-emergent to different classifications of weeds.

Developing a Weed Control Strategy

When you’re developing a weed control strategy for a property, an important detail to impress upon your customer is that it’s not possible to completely eliminate weeds with a single application or cultural practice. There is no silver bullet that kills all weeds and an effective program adjusts to the needs of the property on a seasonal or annual basis.

All weeds have a survival strategy and cannot be completely eliminated because they have different life cycles and methods of reproduction. Seeds can lay dormant for years before they germinate, surviving drought, fire, and herbicide applications. Even if you were to completely clear a property of seeds, seed and vegetative propagules can easily be transported to the property by wind, water, animals or human activity.
As you’re developing or adjusting your weed control strategy, it’s important to ask yourself the following questions:

  • What weeds do you want to control?

  • Is the goal to prevent these weeds, to eradicate them, or both?

  • Are there cultural practices that could help reduce the presence of the weeds?

  • What are the life cycles of the weeds, and when is the proper timing for a pre-emergent herbicide application?

  • What desired plants are on the property, and are the herbicides you’re considering safe/labeled for those plants?

How Pre-Emergent Herbicide Works

To get a better idea of how pre-emergent works, let’s look at 3 key principles of pre-emergent weed control.

Principle #1: Pre-emergent herbicides are designed to control germinating weed seeds.

As its name suggests, pre-emergent is targeted towards weeds that have not yet emerged from the soil. To get the best results and to avoid wasting time and labor cost down the road, the weeds shouldn’t be visible above ground at the time of application.

Important: Pre-emergent is not designed to control existing weeds or weed seeds.

The weed will only be killed when it begins to sprout from the seed and hits the herbicide barrier. It is possible for seeds to remain dormant and not be harmed by the pre-emergent herbicide application. This is why weed control is a constant process. There will always be seeds under the surface and a portion will germinate each season. Annual applications must be made to significantly reduce large infestations.

Remember, pre-emergent herbicide can affect desirable plants. That includes turf. Caution must be taken if you’re applying pre-emergent and seeding the turf in the same season. Seed first, then apply pre-emergent at least 6 weeks later to allow for lawn establishment. Or seed at least 3 months after the pre-emergent has been applied.

Principle #2: Pre-emergent must be mixed correctly and applied evenly over the target area for best results.

Pre-emergent herbicides need to be mixed correctly for the spray solution to be at the appropriate strength. Take the time to read the manufacturer’s recommendations and don’t forget to calibrate your sprayer!

Thorough coverage is key. Think of pre-emergents like a blanket – you need to cover an entire area through which the weed seeds cannot germinate. Spot spraying achieves nothing, as there is plenty of open space for weeds to come through. Manufacturer instructions will indicate how much product to use “per 1000 square feet” or “per acre”, which determines how much herbicide to use for each gallon of water. Note that it usually takes 1 to 2 gallons of spray solution to cover 1000 square feet.

Principle #3: Pre-emergent herbicide must be watered in.

Watering in activates the herbicide, creating a barrier just below the surface. Most products call for 0.5 inches of irrigation or rain within 21 days after application.

If you’re working with a non-irrigated area or a drip zone, apply the pre-emergent just before rain is anticipated.

Applying Pre-Emergent to Different Classifications of Weeds

To know when to apply pre-emergent herbicide, it is important to know how weeds are classified, namely by their life cycles.

Weed Classification: Summer Annuals

Most well-known example: Crabgrass (Crabgrass Germination Map below)
Other examples: Lambsquarters, Mallow, Pigweed, Spurge
Life Cycle: 1 year – Germinate in spring. They flower, produce seed, then die in fall.
Pre-emergent timing: Early spring (late winter for Southern & Coastal U.S.)

Weed Classification: Winter Annuals

Most well-known example: Annual Bluegrass (Poa Annua)
Other examples: Shotweed, Chickweed, Mustards.
Life Cycle: 1 year – Germinate in fall. Flower and produce seed quickly, then die in spring.
Pre-emergent timing: Late summer/early fall (rule of thumb is by September 15th)

Need help choosing the right pre-emergent herbicide for your Spring application?
Contact your local Horizon store. We’re happy to help!

Free Landscape Maintenance Guide

Prevention is the Best Medicine

An expanse of green, unblemished turf is a splendid thing to behold. The average person taking in such a scene may not realize just how much work goes into creating that gleaming emerald carpet.

When a landscape professional looks at that lawn, however, he sees the pounds of fertilizer that were spread, the irrigation that was carefully scheduled, the mowing that was done to just the right height, the aerating and the dethatching that allowed sun and air to get to each blade of glass, the insecticide that killed the grubs that nibble grass roots, and finally, the herbicides that were used to prevent or remove the weeds.

Weeds, like party crashers, may show up uninvited, and never alone, but with a gaggle of their annoying friends in tow. When they appear, they’re like the girl whose hair, dress and makeup are perfect, but when prom night comes, finds a big, red zit on the tip of her nose. Then, it’s a last-minute scramble to cover up the eyesore.

It would have been better to prevent the pimple from forming in the first place, but as every teenager knows, that’s hardly an exact science.

We’re luckier when it comes to weeds; they’re fairly predictable. We know when they’re going to show up, more or less. Then we can hit them with herbicides, in granular or liquid form.

There are two ways to attack weeds: before they appear (pre-emergently); and after they appear (post-emergently). Which plan of attack works best depends on which species you’re dealing with, your weather and other factors. But in general terms, pre- tends to be better than post-.

“Annual weeds that grow each year from seed are easier to prevent with pre-emergents than perennial weeds that grow back from roots,” says Ashton Ritchie, a lawn and garden expert at the Scotts Miracle-Gro Co., Marysville, Ohio.

Commonly occuring spring-germinating annual summer weeds include crabgrass, foxtail, barnyard grass, spurge and oxalis. They mature during warm weather, produce their seeds and then die with the first frost.

Poa annua, smooth chickweed and henbit are common winter annual weeds that germinate in early fall and mature during cool weather, producing seed in the spring, and then dying out during the hot summer weather.

Both grassy and broadleaf weeds are a problem for Kevin Herrmann, general manager of Fairway Green Inc., in Raleigh, North Carolina. “We have a big issue with a broadleaf called chamberbitter. It’s a weed that came out of Florida about 15 years ago, probably from pine straw. It’s just running rampant. We have a relatively new one that’s been around for the past eight to 12 years, called doveweed. And of course, there’s always Poa annua and crabgrass to deal with, too.”

In Tumwater, Washington, it’s a different weed that struggles for dominance over landscapes. “By far, the worst one we deal with is horsetail,” says Chris McCallum, landscape maintenance director at Controlled Rain LLC.

“It’s one of the oldest plants known to man, and it grows like asparagus, by stolons. The roots are so long that you can’t get a good contact herbicide to translocate (travel through the plant’s phloem) long enough to kill it. You may burn the root back, but you won’t get total kill.”

The tough-to-control weed has been known to grow right through asphalt. And because of the way it propagates, disturbing a site through excavation or rototilling causes it to spread like wildfire; every cut root segment becomes a new plant. McCallum says that, compared with horsetail, controlling crabgrass is “child’s play.”

The only pre-emergent herbicide he’s found to be effective on horsetail is dichlobenil. But it can be rough on the other plants in the landscape, especially in beds. “You have to apply this stuff sparingly,” says McCallum.

When should you start?

What’s the earliest you should start laying down pre-emergent controls? That depends on where you live. In the northern climates, such as the Midwest and Northeast, many companies start in early winter, just before the snow covers the ground.

Mike Friederichs, president and co-owner of Pro Landscape Maintenance LLC, Waconia, Minnesota, prefers to wait until early spring. “We always target April 1 as our start date,” he says. “That’s weather-dependent, of course. There have been years where we’re still plowing snow in April. But generally, we’re looking at a six- to eight-week application period starting on that date, wrapping it up by mid- to late May.”

Mostly, Friederichs battles crabgrass, and his chemical of choice is a granular formulation of dithiopyr. It’s also effective on goosegrass, Poa annua, bittercress, oxalis, chickweed, henbit and spurge.

“We use it because it’s a pre-emergent with post-emergent qualities as well,” says Friederichs. “It works up to the second or third tiller (a shoot that springs from the root or bottom of the original stalk) stage.

“Being that it’s a granular product, we’re able to apply it early, and have a long residual. If things start running late, we’re still able to get control. That’s important because it’s very hard to fight crabgrass once it reaches middle- to late-stage development.”

“The type of pre-emergent we use breaks down microbially,” says Mark Wise of Kiefer Landscaping Inc., Durham, North Carolina.

“Once the temperature gets around 57 degrees, it actually prunes the roots and kills the plants as they start to grow. A lot of people think it keeps weeds from germinating, but that’s not the case.”

Herrmann does his first application in mid-January. “We do splitouts (split applications). Because people tend to mow fescue too short, not giving it enough competition against the crabgrass, we’ve gone to three applications of pre-emergent, with the second around March 15, applying the same amount as the first one. The third will be at a much lower rate, around the first of August.”

“The best efficacy we’ve seen is in split application,” confirms Willie Pennington, a sales representative for BASF, the multinational chemical company hose U.S. headquarters is in Florham Park, New Jersey. “It works much better than one single application.”

Pendimethalin is supposed to be applied at a rate of 3 pounds per acre, but a weed scientist will tell you it is preferential to apply 1.5 pounds initially, followed by another 3.5 pounds four to six weeks later. “You’ll see much better control of Poa annua and crabgrass than you’ll get with a single application,” he adds.

The special case of crabgrass

The conventional wisdom is that crabgrass must be tackled pre-emergently, or not at all. Herrmann disagrees with that notion. “There are some new formulations that do an okay job with it on a post-emergent basis, as long as you catch it pretty early. If it gets to a mature, multileaf stage, it becomes very difficult to control.”

That’s true of some of the other broadleaf and other grassy weeds, too, according to Herrmann. When it starts getting really hot, the waxy cuticle layer on the leaf tissue builds up and makes penetrating it with a post-emergent herbicide difficult.

“Summer annuals like crabgrass germinate like waves hitting a beach,” says Ritchie. The first crabgrass will sprout next to a sidewalk, or on a south slope, where the soil first warms to 55 degrees in the early spring. The next wave to germinate will be where the lawn is thinner; the sunlight and warmth helps the seed get started. The last crabgrass plant will sprout in early to midsummer in newly exposed soil.

To do the best job preventing crabgrass, your pre-emergent should have been spread by the time all the yellow blossoms fall off the forsythia bushes, the lilacs begin blooming, or you’re starting to see dandelion puffballs.

Most pre-emergent herbicides will kill crabgrass seedlings a few days after sprouting when they are still at the two-leaf stage. There are post-emergents containing quinclorac that will kill young crabgrass and other broadleaf weeds after they grow.

Resistance and adaptation

It’d be nice if we could just keep spraying weeds with the same herbicides, year after year. Unfortunately, it doesn’t work that way. Most of the weeds will be killed by the chemical, but a few won’t. Their descendants will be resistant to that particular herbicide, and eventually, the dominant culture. So to kill them, you’ve got to change your plan of attack.

That’s where ‘mode of action’ comes into play, the means by which the chemical kills the weed. For example, dithiopyr acts as a root growth and cell division inhibitor, while pendimethalin inhibits both root and shoot growth, preventing plant cell division and elongation.

Dichlobenil is a cell division inhibitor, prodiamine inhibits plant cell growth, and mesotrione interferes with an enzyme that protects chlorophyll from decomposition by sunlight.

There is a way to break up the resistance/adaptation cycle. If you use an herbicide with one particular mode of action this season, use one with a different mode of action next year.

“If the weeds get to the point where they’re truly resistant to anything you’re using, I’d use glyphosate to clean up and start over,” says Pennington.

Are you sure it’s resistance?

Sometimes, you may think you’re encountering resistance when you’re really dealing with another problem. There are some other possibilities to consider, especially when it comes to crabgrass, where resistance isn’t all that common.

Friederichs has used a dithiopyr-based herbicide on crabgrass for 14 seasons in a row and hasn’t noticed any resistance developing. “Any issues we’ve had were environmental. It could have been the soil composition, or the weather; one year, it was 80 degrees on St. Patrick’s Day. At times, we’ve had very wet springs, with lots of rain, where the herbicide simply washed through the effective zone or became diluted.”

If a granular pre-emergent is spread too lightly, or areas are missed, prevention will not last as long as expected. Coverage can be more hit-or-miss with a large-granule formulation than with smaller-granule types.

If the product was put down too late, you may see weeds popping up near a sidewalk or on a south slope where the soil warmed faster, and the seeds started to sprout before the application of the herbicide.

Was the soil disturbed after you applied the chemical? That just spreads the seeds, especially of crabgrass, and then they’re off to the races. Was the pre-emergent properly watered in? It’ll be less effective unless the lawn gets a ¼- to ½-inch of water within two to three days of application. Grass that’s mowed too short, or thinned by drought, insect or fungus attack could let crabgrass germinate if the preventer is no longer active.

Make sure which weed you’re really dealing with, and that it’s not a look-alike. For instance, dallisgrass and nimblewill are often mistaken for crabgrass, but are much more difficult to prevent.

Some premium organic landscape services will hand-pull weeds. That’s labor-intensive and probably not permanently effective. If any part of the root is still in the ground, the weed will come back. That’s especially true of weeds that propagate via rhizomes or stolons. You might pull the head off, but it’ll grow another.

Hand-pulling isn’t economically feasible in most cases, anyway. As Wise puts it, “Paying eight guys for a whole day of pulling weeds costs a lot more than paying one guy with a spreader and a $150 bag of pre-emergent.”

Weed control in landscape beds is a bit different. Much depends on what types of plants are in the beds. If the bed contains permanent, small ornamental plants, vines, hostas, perennials, and even some trees and shrubs, you can use sprayable or granular pre-emergents.

But use caution if it contains annual plants, flowers or woody ornamentals. Tender plants with shallow root systems can be damaged by herbicides. In Friederichs’ opinion, the best weed control in a landscape bed is prevention. He prefers laying down a thick layer of hardwood mulch, such as cypress chips, every year.

Overseeding

When it comes to preventing weeds in turf, a lot of professionals rely on overseeding, which is really nothing more than spreading grass seed over an existing lawn, to fill in sparse patches. It’s a technique that can be worth many pounds of herbicide. The healthy grass simply outcompetes the weeds.

Cool-season grasses such as tall fescue, fine fescue, perennial and annual ryegrass, and sometimes, bluegrass, are the main candidates for overseeding. It’s not generally done over grasses that spread via runners unless they’re damaged or diseased. One exception is Bermuda grass. It’s occasionally overseeded in the fall with a cool-season variety.

The war against weeds will never be entirely won. But, police actions can keep their incursions in check. Pre-emergents, locked and loaded, are some of the best weapons we have against them. Aim them wisely.

The author is senior editor of Irrigation & Green Industry and can be reached at [email protected]

Five Things You Need to Know About Pre-Emergent Weed Control

What is the purpose of Pre-Emergent Weed Control?

Pre-emergent weed control is designed to prevent a variety of weeds before they appear. This is achieved by applying a protective layer of pre-emergent herbicide to your lawn, preventing the weeds from penetrating the soil barrier.

When Should I Apply Pre-Emergent Weed Control?

Throughout areas of the southeastern United States, like Raleigh, NC, it is important to apply pre-emergent weed control during the right time of year. If the herbicide is not applied prior to germination, it is not effective. This means the protective barrier MUST be applied before weeds have the opportunity to germinate.
At Canopy, we like to apply the first round of pre-emergent before “the dogwoods start blooming”. It can be weather dependent, but typically the best time to apply a pre-emergent weed control treatment in the southeast is during the months of February and March.
After March, you will be less likely to see good results from a pre-emergent weed treatment. The exception here of course, would be if it had been a particularly cold season, leaving seeds dormant longer.

How Long Does Pre-Emergent Weed Control Last?

‍Every product is a bit different. Typically, you can expect one treatment to last 3-5 months. However, Canopy recommends applying a split application approximately one month apart to maximize effectiveness.
It is also important to select a good product. If you are planning to try and treat your lawn yourself, always be sure to read the labels, so you understand how long the manufacturer suggests their product lasts. A professional landscaper will be able to answer this question for you.

What Types of Weeds Does Pre-Emergent Weed Control Treat?

Pre-emergent weed control is effective prior to germination on most all summer annual weed varieties. This includes common weeds like crabgrass.

Can Pre-Emergent Weed Control Harm My Lawn?

Pre-emergent weed control is not harmful to your lawn. If you plan to plant new seeds for ornamental plants to compliment your landscape, or new grass seed to your lawn, treatment should not be applied to those areas prior to germination.
Canopy’s professional landscape teams will take the time to answer any questions that you may have about herbicide treatments, the best time to apply them and what areas you should avoid.

Lawn Solutions Oxafert – Pre-Emergent herbicide and fertiliser

A revolutionary and unique domestic product that acts as a PRE-EMERGENT herbicide and a fertiliser.

Applied correctly, the pre-emergent herbicide component will kill stubborn annual weeds before they appear, whilst the fertiliser component will provide the necessary nutrients to keep your lawn looking greener and healthier all year-round.

The idea of using a pre-emergent herbicide is to target weed seeds before they take hold by forming a barrier at soil level that affects the germination of any new seedlings. The new combination fertiliser and pre-emergent product provides an ideal mechanism to take the herbicide to just under the soil and the fertiliser helps give a quick boost to your lawn. Controlling both broadleaf and annual grass-type weeds, the pre-emergent herbicide works by stopping any new seedings in their tracks – yet won’t inhibit any root growth of your established turf. The herbicide active ingredient has a residual effect for around three months, so is ideal to apply seasonally to coincide with the different weed types throughout the year.

It’s a lawn care practice that will take some time to get used to as there won’t be any results in applying to already weedy lawns – it will only prevent any new ones from forming. So, it’s a use beforehand type of remedy and if you’ve got a lawn full of weeds now then try and use a control now to get them under control and then look at applying the pre-emergent on a regular basis to keep them under control. Keep in mind however, that keeping a good performing lawn in good condition through regular maintenance and fertilisation will help keep weeds at bay and is a better option than trying to control weeds by spraying all the time. Lawn Solutions OxaFert Herbicide & Fertiliser is a pre-emergent herbicide for control of many annual grasses and broad-leaf weeds in warm season turf.

For more information on Oxafert take a look at the Lawn Store

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What Are Pre-Emergent Herbicides: Tips On Using Pre-Emergents

Even the most vigilant gardener will have a weed or two in the lawn. Herbicides are useful in the battle against annual, perennial and biennial weeds, but you have to know when to use them and which ones are most effective against a particular weed problem.

Pre-emergence weed killers are used on established lawns as part of an annual effort to combat plant pests. What are pre-emergent herbicides? These chemical compositions are used before weeds take hold to kill off infant root systems and keep them from growing. Learn how pre-emergent herbicides work so you can decide if they are the right method for you.

What are Pre-Emergent Herbicides?

Pre-emergence weed killers are used before you see the weeds to prevent them from showing up in the garden or lawn. This doesn’t mean the chemicals interfere with germination but rather they stop the formation of new root cells in baby weed plants.

Without weeds, the seedlings cannot continue to feed and grow and they just die back. This whole process happens at the soil level under the blades and thatch of the grass so you

don’t ever have to see the sprouted weeds. Timing, weather and the type of weeds that are problematic in the garden will dictate the exact formula and application for using pre-emergents.

How Pre-Emergents Work

The chemicals in pre-emergent weed killers are not effective on vegetative buds that sprout from existing roots or rhizomes. They also cannot be used on a prepared grass seed bed because their root stunting action in young plants will also affect sprouting grass.

Established plants have nothing to fear, as their root system is already developed and the plant is hearty and healthy. Pre-emergent info indicates that it is the sensitive root tissue of newly germinated seedlings which is killed off, resulting in complete plant death.

Perennial weeds develop thick persistent adult roots that re-sprout in spring, which makes them difficult to control with a pre-emergent formula. Annual weeds are in two classes: winter and summer annuals. The timing of a pre-emergence weed killer for each must match the germination period for the variety of weed. Biennial weeds, like dandelions, are not controlled by a pre-emergent because they produce seed that germinates nearly year around.

Pre-Emergent Info for Applications

As with most plant chemicals, the weather and type of weeds will affect the application method. When using pre-emergents for winter annuals, apply in fall because that is when the seeds germinate. Summer annuals germinate in spring and that is the correct time to apply a pre-emergent. If you are unsure what type of weed is the most troublesome, it is a safe bet that a springtime application will control the majority of the pests.

Pre-emergent weed killers require water to activate them and carry the chemical down to the root systems of newly sprouted weeds. Never apply an herbicide spray when there is a wind to prevent injury to other plants. The ambient temperature must be above freezing and the soil should be workable. Consult the manufacturers label for the varieties of weeds the product is effective against and the method and timing of application.

Weed Prevention using Pre-Emergent Herbicides

Pre-emergent herbicides, sometimes referred to as crabgrass preventers, are effective ways to prevent an undesired weed problem before it starts. This article explains pre-emergent herbicides, and when to apply them.

Pre-emergent herbicides are chemicals that prevent undesired weeds in your lawn. They do not prevent the germination of the seed, but help control it so that it will not sprout. Due to the way these herbicides work, application timing is the most important aspect of weed prevention success. If the weed has already sprouted and is visible, pre-emergent herbicides will not solve the weed problem. For a summary of pre-emergent active ingredients, go to Pre-emergent Herbicides

There are a few exceptions because some chemicals include active ingredients that work as both post (after the weed sprouts) and pre-emergent herbicides such as Dithiopyr.

Top Dithiopyr Product Recommendations


Hi-Yield Weed and Grass Stopper

Dimension 2EW

Dithiopyr 40 WSB

When to Apply Pre-Emergent Herbicides?

Early Spring and Fall are the most effective times to apply pre-emergent herbicides. They can be applied throughout the year, and will still prevent new weeds that sprout, however most weeds sprout during spring and fall. Spring applications target different weed species than Fall applications, so it is very important to know the type of weed you are trying to prevent for best results. See below for help identifying your target weeds.

Spring Herbicide Application

Spring pre-emergent herbicide applications are used to prevent summer annual weeds. Summer annual weeds are both grassy and broadleaf types. For best results apply herbicides when the soil temperature is around 55 degrees or above for at least 36 to 72 hours (ideally this will be two weeks before seed germination). The majority of the USA experiences these soil temperatures from March to April. Consult your local county extension service to get up to date soil temperatures in your area. Here is a map that gives a good idea of when to apply in the part of the country you live in.

Using granules or liquid formulations are the two primary manners to apply herbicides. If you use granular pre-emergent herbicide it is very important to water the chemical into the ground because the active ingredient needs to penetrate the soil. The herbicide is trapped by the granule until it is activated by water. This is also true with liquid pre-emergent products because grass and other plants may trap the active ingredient keeping it from reaching the soil during the initial application.

Common Annual Summer Grassy Weeds


(Crabgrass Pictures-NY State IPM Program)

  • Crabgrass
  • Goosegrass
  • Barnyardgrass
  • Sandbur
  • Foxtail

Common Annual Summer Broadleaf Weed

  • Yellow Woodsorrel


    Picture: (bio.brandieis.edu)

  • Clover
  • Carpetweed
  • Black Medic
  • Spurge
  • Knotweed
  • Ragweed

Spring Pre-Emergent Product Recommendations


Surflan Pro
XL-2G Quali-Pro T/I

Fall Herbicide Application

Fall pre-emergent applications are designed to prevent winter annual weeds. These weeds germinate during the fall months. Similar to spring applications, timing is very important to successfully prevent winter annual weeds from taking over your lawn. The best time to apply fall pre-emergent herbicides is late summer to early fall depending on your geographic location.

Annual Bluegrass (Poa Annua) is one of the most common winter annual weeds. Annual Bluegrass is a hardy weed, and may require multiple applications over consecutive seasons to achieve an acceptable level of control. Fall weeds being to germinate when soil temperatures starts to dip below 70 degrees (soil temperatures about 50 degrees). The best time to apply is the when the daytime highs drop to the mid-70s for about three to five days in a row.

Since a pre-emergent application will not last through the following summer, make a pre-emergent application late spring or early summer (see Spring Herbicide Applicaiton map).

Other common winter annual weeds include:

  • Prickley Lettuce

    Picture: Flickr, Richards
  • Henbit
  • Common Chickweed
  • Deadnettle

Fall Pre-Emergent Product Recommendations

Prodiamine 65 WDG Dithiopyr 40 WSB

Vegetable Garden Weed Control

Judging from the number of Hortline calls concerning weed control, 1993 must have been the year of the weed. Gardeners have several options when it comes to controlling weeds in the vegetable garden. The oldest method of weed control comes with cultivation, either hand hoeing or through the use of a rototiller. Cultivation works well for annual weeds such as crabgrass or purslane. However, with perennial weeds, cultivation may initially create a larger problem. Cultivation breaks perennial weeds and their root systems into smaller pieces which grow into entire plants. Frequent cultivation is often needed to control perennial weeds. Be sure to remove as many weed parts as you can so the weeds are not allowed to reroot and grow. A second disadvantage of cultivation is that many vegetables have shallow root systems. Frequent cultivation can damage their roots and reduce potential yields. Use care when cultivating around such plants as squash, cucumbers, melons and tomatoes.

Mulches, both organic and synthetic, can be quite effective in reducing or eliminating annual weeds. Synthetic mulches, such as black plastic, are also effective for controlling perennial weeds. Unfortunately, most perennial weeds have enough food reserves to push through a layer of organic mulch. Mulches prevent light from reaching the soil surface and inhibit weed seed germination and growth. Mulches also conserve moisture, prevent erosion, and reduce soil compaction. Organic mulches also keep soil temperatures from rising to high levels. Apply organic mulches, such as grass clipping, straw, or shredded leaves, after the soil has had a chance to warm in the spring. Warm season crops require warm soils for good growth. Another advantage of organic mulches is they return valuable organic matter to the soil as well as small amounts of nutrients.

A final method of weed control involves the use of herbicides. Both pre-emergence and post-emergence herbicides are available for use in the garden. Pre-emergence herbicides are an effective way to control annual grasses and some annual broadleaf weeds. Pre- emergence herbicides work in different ways to prevent the seedling from emerging through the soil surface. Two pre-emergence herbicides are commonly used in the home garden, Dacthal (DCPA) and Treflan or Preen (trifluralin). Both control a number of weeds and can be used with many garden vegetables and flowers. It is important to remember that neither one can be used with every garden plant. Be sure to read the label for a list of vegetables and the proper vegetable plant stage for herbicide application. If your particular vegetable is not on the label, the product can not be used. Another type of herbicide commonly used in the vegetable garden is the non-selective herbicide, glyphosate (Roundup or Kleenup). Glyphosate can be used in the garden prior to planting several garden vegetables. After 7 days, the seeds, rooted cuttings, or transplants of many garden vegetables can be planted. The biggest exception is tomatoes. Tomato transplants cannot be planted for 30 days; however, seeds may be planted 7 days after the use of glyphosate. Again, the label lists the plants and proper waiting intervals for planting.

The 1994 gardening season looks like a year for retaliation after a gardening season lost in 1993. Through the combined use of the weed control methods listed above, I hope this summer will be enjoyable instead of back breaking.

This article originally appeared in the April 27, 1994 issue, p. 53.

Weed Control

Weeds (plants growing out of place) are a serious garden problem. They rob vegetable plants of sunlight, water, and nutrients. They also provide hiding places for insects and serve as a source of vegetable diseases.

Weeds can kill a gardener’s enthusiasm, which can cause them to abandon the garden in midsummer. It is important to control weeds while they are small and before they get out of control.

Since any plant growing out of place can be considered a weed, a sweet corn plant (from a carelessly dropped seed) growing in a row of bush snap beans is technically a weed; but the most common garden weeds are crabgrass, yellow and purple nutsedge, morningglories, bermudagrass, and pigweed.

Most weeds can be controlled and kept from becoming serious problems in the garden. Methods of control include hand-pulling, cultivation, mulching, and use of chemicals.

Hand-Pulling

Hand-pulling is not an effective way to control weeds in a large garden, but it can be effective under certain circumstances. Hand-pull weeds that appear in the row with vegetable plants, as well as those that grow in the planting holes of a plastic mulch.

Weeds that grow between closely spaced rows of vegetables in wide rows, raised beds, or small gardens also may require hand-pulling. Weeds growing in containers used for vegetables should be hand-pulled. Extremely small weeds are difficult to pull by hand, but do not wait until the weeds get so large that pulling them destroys adjacent vegetable plants. Thinning seedlings spaced too closely together and hand-weeding frequently can be done at the same time.

Cultivation

Cultivation is the most widely used method of garden weed control. It is not a one-time chore, for with each rain, irrigation, and stirring of the soil, weed seedlings emerge.

A variety of hand and power equipment is used for cultivation, but the most commonly used tools are the hoe and garden tiller.

A sharpened hoe blade is an excellent tool for cutting the roots of weeds. The severed plants dry in the sun and die.

A garden tiller and other soil-disturbing tools, the hoe included, are used to disturb the soil around the weed plant’s roots. On a hot day, the weeds die when their roots dry and the plants are unable to get water. Small weeds die more quickly than large weeds, so cultivation should be frequent enough to prevent weed seedlings from becoming established. Cultivation should also be shallow so you do not disturb or injure vegetable plant roots.

Deep cultivation, in addition to destroying weeds, injures vegetable plant roots and brings more weed seeds to the surface, where they germinate. “Hoe blight,” the wilting and death of vegetable plants after cultivation, often results from careless cultivation.

Take a perennial weed, such as bermudagrass, out of the garden following cultivation because pieces of the plant that have no roots can form roots and make the bermudagrass problem worse.

Mulching

Mulching is an effective way to control garden weeds. Natural and plastic mulches properly applied to weed-free garden soil prevent most weeds from becoming established in the mulched area. Bermudagrass and nutsedge are difficult to control completely with mulches. Weeds that appear in the planting holes of plastic mulch should be pulled by hand.

Herbicides

Commercial vegetable growers have a fairly wide choice of chemical weed killers (herbicides) to prevent or control weed problems. Gardeners, however, have a much smaller choice of herbicides.

Don’t expect to control all weeds in a garden of mixed vegetables with one herbicide. First, no single herbicide controls all weeds. Secondly, some vegetables are also sensitive to the herbicide, and if the wrong herbicide is used, the vegetable is injured along with the weeds.

Herbicides applied to the soil before vegetables are planted and before weeds have emerged are called preemergence herbicides. Some preemergence herbicides can be applied immediately after the vegetable seeds or plants are planted but before the weed seeds germinate. Postemergence herbicides are applied after weeds have emerged.

Herbicides used in the garden may be in the form of granules, wettable powders, or liquids. The equipment needed for application depends on the formulation used. Use a pump-up pressure sprayer for applying liquids and wettable powders. Since most garden sprayers are equipped with a cone-type nozzle, use a 50-mesh screen and a 8003 E or equivalent fan nozzle attached to the sprayer for applying herbicides.

Chemical herbicides used in the vegetable garden can be washed from the sprayer, but some of those used on the lawn cannot. Therefore, a wise gardener will keep two sprayers: one for lawn herbicides and the other for garden herbicides. When spraying herbicides approved for application over the tops of vegetable plants, do not use a sprayer that has been used with lawn herbicides.

Before using a herbicide in your garden, read the product label for a listing of vegetables it can be used on, the recommended rate of application, and the method of application. Never use a product that is not labeled, and do not exceed the recommended rate.

Dacthal—Several brand names are available. Dacthal can be used on a wide variety of vegetable plants. Applied correctly, Dacthal gives good control of most grasses and a few broadleaf weeds. This herbicide controls weeds as their seeds germinate. Therefore, before applying Dacthal, remove existing weed plants.

Trifluralin—Several brand names are available. Trifluralin is a preemergence herbicide used to control grass problems in the garden. Some planning of the garden to group trifluralin-labeled vegetables in one area is helpful when you use this herbicide. To obtain good weed control, mix trifluralin with garden soil. Cultivate soil to eliminate clods. Broadcast the recommended amount of either the granules or the liquid formulation. Granules are easier for most gardeners to use. After application, mix the herbicide in the top 2 inches of the soil. Two very shallow cultivations provide good mixing with the soil. Trifluralin is labeled for use before planting seeds of several vegetables and before setting transplants of others. Read the package label for a list of approved vegetables.

Poast is a postemergence herbicide that selectively controls grass weeds in several vegetables. Apply Poast to most grasses before plants reach 8 inches high. One application controls most annual grasses, but several applications may be required to control perennial grasses like bermudagrass. Mix a crop oil concentrate in the spray solution before application. Read the Poast label for specific instructions and approved vegetable crops.

Glyphosate—Formulations of this popular nonselective, postemergence herbicide are approved for limited use in the vegetable garden site. Most applications are for eliminating existing weed problems before vegetable seedling emergence and before vegetable plants are in the garden. Read the label for specific application instructions and limitations.

Nozzle Parts

The best pre-emergent weed control practices focus entirely on prevention. If the weeds never grow, they can’t spread to new areas of your lawn. For that kind of program to work, the treatments must be applied before the seeds of weeds germinate.

Saying Goodbye to Summer Weeds

One of the most aggressive summer weeds in Georgia is crabgrass. It will put even the best pre-emergent weed control products to the test. Once it arrives, it quickly eats up half of your yard. That’s especially frustrating for homeowners who thought they were properly treating their lawns to prevent it from sprouting.

The problem is that many of the best pre-emergent weed control products are mislabeled for the weeds you’re trying to fight. While many sprout at 52 degrees, crabgrass germinates at 50. Therefore, the time to apply your pre-emergent treatment may be weeks earlier than you realize. Those in the Cummings area should be safe applying treatments in early March. However, many in the southern part of the state would have missed the ball by then.

Winter Weed Control: When to Apply the Best Pre-Emergent Weed Control Products

Chickweed, bluegrass and other common winter weeds germinate in early fall. You should apply your pre-emergent formulas in early to mid-September. You want to do this before you aerate your lawn or apply the last fertilizer of the season. You’ll also want to keep your pre-emergent formula separate from any lime you might be adding to your yard’s soil.

Professional Pre-emergent Schedules

As much as you may love your lawn, chances are you don’t want to go through the rigor of applying treatments every weekend or even once a month. If you did, sourcing the best products would be next to impossible without professional credentials. As part of the consumer market, you’re forced to settle for products that are safe to use, moderately effective, and generally easy to apply with traditional yard working tools. The same isn’t said for professionals.

Pros have a wider range of products available—as well as the tools and training to put them to best use. You may even find your lawn care provider has a different schedule for pre-emergent maintenance. Some clients become concerned that they don’t need as many treatments as they’re receiving, and they worry unduly over health or budget concerns. They forget that the treatments available to consumers are quite different from what is used by industry pros.

For instance, you may only do two applications a year using a slow-release formula, which also fertilizes your lawn. A professional may begin treatments in winter, applying pre-emergents for crabgrass twice before the temperature rises high enough for seeds to germinate. The next treatment may be aimed at controlling broadleaf weeds or crawlers that stay dormant until temperatures rise. In fall two pre-emergent treatments are typically needed for winter grass weeds and other common invasive growers.

These types of treatments allow for fighting weeds as they really develop and grow, without the need for convenience built into so many consumer products.

Now that we’re into early spring, it’s tree and shrub trimming time. Just don’t forget about the best pre-emergent weed control methods. If you’d rather leave this task to the pros, just Think Green! Call us at (678) 648-2556 today.

Developing Your Spring Fertilization Program

This photo shows a yard with one side treated with pre-emergent herbicides and the other side untreated.
Photo: Bayer

When it comes to applying pre-emergent herbicides, customers can sometimes be split on whether or not this service is necessary or even helpful.

To help shed some light on the subject, experts in the green and chemical care industry have weighed in on how pre-emergent herbicides work, why they are helpful, the equipment required to apply them, when to apply and which myths have merit and which are way off base.

How they work

For starters, let’s talk about how pre-emergent herbicides actually work. There are many different types of pre-emergent herbicides, and they can vary in carriers and chemical formulations.

They are applied to the soil either as a spray in the form of a liquid or spread as a granular. Once these herbicides are irrigated properly into the soil, a chemical barrier is formed, which controls the weeds as they germinate.

“With pre-emergent herbicides, you’re typically going to make a broadcast application to control weed seedlings after they germinate but prior to emergence – when the seedling puts out a shoot and root,” said Laurence Mudge, Bayer Green Solutions team manager. “Pre-emergent herbicides then offer residual control as seeds germinate throughout the season, effectively stopping the weed from ever ‘emerging’ from the soil.”

Are they profitable?

While this answer could vary from business to business, Kevin Roper, account manager with Landscape Workshop, LLC, has found pre-emergents to be extremely useful in his practice.

“Our company offers this service as part of our regular maintenance service,” Roper said. “Having effective weed control on a property not only looks great from a customer’s standpoint but also saves countless labor hours of hand pulling weeds and can reduce (the) frequency of mowings and string-trimmings needed.”

If your company doesn’t offer this service yet but has seriously considered it, there are a few things to consider before jumping in.

Roper highly encourages other landscapers to take into consideration the upfront costs of the products you’ll be using and the application methods you’ll be using. It’s also smart to be well acquainted with the types of weeds prevalent in your area so you are able to pinpoint the exact products you’ll need to fight them.

“Properly researching the chemical labels, asking suppliers and talking to extension services will help you decide,” Roper said. “Also, make sure that you have met the applicator licensing requirements prior to making any applications.”

When it comes to required equipment, Roper suggests the use of either a truck or trailer capable of holding a spray tank, engine, pump, hose reel and hose if liquid is your best option.

“There are some really nice 200 gallon, fully assembled units available that slide into a full-size pickup truck,” Roper said. “We have one of these that we often use. Having the spray unit all contained inside a bed of a pickup truck allows ease of access to most properties.”

Mudge recommends the use of a broadcast sprayer when servicing larger areas and the use of a backpack sprayer for smaller areas. When using granular products, Mudge says landscapers have the option of choosing a type that’s either impregnated on a fertilizer or a non-fertilizer formula. When this is the case, Mudge recommends the use of a push spreader, handheld sprayer or, for larger areas, a tractor-mounted applicator.

Liquid versus granular

Whether dealing with liquid or granular formulations, Mudge says that herbicide distribution is extremely important.

“Liquid applications by default deliver better herbicide distribution,” Mudge said. “Granular formulations, particularly on fertilizer, can vary in particle size, the spread rate (or amount of product per acre) and the particle distribution. With some fertilizer products, you’ll get fairly large particles and low spread rates that can actually allow weeds to germinate in between them. But there are some granular products…that have much smaller particles for improved distribution.”

Mudge adds that another big difference between liquid and granular pre-emergents is that more water will be required when using granular formulations, as it takes more water to get the herbicide off the granule and down into the soil.

For Roper, liquid formulations have proven to provide the most uniformed coverage for his customers, however, he does understand that liquids aren’t always an option for some areas.

“Some properties may have courtyards or areas that are not accessible by a spray hose,” Roper said. “If that’s the case, applying a granular product with a push spreader may be a better choice. Also, if you are offering a weed control service for shrubbery bed spaces, granular applications are a much faster method of delivery. Working in and around trees and shrubs with a hose can be a challenge. Hand or belly crank spreaders allow you to quickly apply granular products to beds.”

When to apply and what to charge

The next pressing questions surrounding pre-emergents are when do they need to be applied and how much should I charge for this service?

Mudge and Roper both recommend applying pre-emergents twice a year, once in the late winter/early spring going into summer and again in the fall.

“These times are critical to target (and) avoid seasonal seeds from germinating,” Roper said. “So, start offering your potential customers your service in the summer and winter. Turf weed control usually requires multiple applications throughout the year to achieve the best finished product. It is best to sell this service as a timed program to have the consistent weed-free look that customers are wanting.”

Roper adds that you can also customize the program based on the type of turf that will be treated and the needs of your customer by suggesting insecticide, fertilizer or fungicide applications.

As far as pricing is concerned, Roper says for his company the prices are set by the size of the area, such as acres or square feet. Roper also suggests calculating how long it takes your applicator to set an area consistently to generate labor costs.

“Also, the difficulty of the job may be a factor,” he adds. “A perfectly square acre will be much faster to treat than an acre of turf that is divided up in parking lot turf islands at a busy mall.”

Common myths

When it comes to myths associated with pre-emergent herbicides, some of the most common are:

  • If you don’t have weeds, you don’t need to use pre-emergent herbicides
  • If your lawn is thick, you don’t need to use them
  • Soil aeration can break down the barrier and cause more weeds to grow
  • There’s no reason to treat an entire area; spot treatment will suffice
  • All pre-emergent herbicides are created equal
  • Herbicide applications alone are all you need

Starting from the top of the list, Mudge and Roper share their insights to help determine which of these are fact and which are fiction.

Even if your customers don’t have weeds right this minute, that doesn’t mean they won’t have them in the future. Therefore, the first myth is false, according to both experts.

“If you don’t currently have weeds, chances are, you will,” Roper said. “Seeds invade properties from many sources. Wind, encroaching neighboring areas, mowers and even wildlife can promote undesired weed growth in your turf. You really should invest in weed control before a problem arises.”

If your customers have a lawn that is covered in thick grass, they may be tempted to decline this service based on the second common myth. While thick lawns may help hold weeds off longer than thinner ones, it won’t keep them gone forever. This myth, therefore, is also false according to the experts.

“A healthy lawn tends to help with reduction in weeds and helps pre-emergent herbicides work better,” Mudge said. “A lot of weed control is plant competition. Just because you have a thick lawn doesn’t mean you won’t have weeds – so in many cases, you’ll still want to use a pre-emergent herbicide, though you may be able to get by with a lower rate.”

When talking about soil aeration disturbing the weed barrier and causing more weeds to grow, Roper says it’s sort of a yes and no deal. Because the aeration pulls the plugs up, the soil underneath each plug is then left with no chemical protection. This leaves areas in place but not exposed to potential problems, and Roper suggests aerating the turf before any application to keep the barrier undisturbed.

“You’d think that aeration might break down the weed barrier and cause a problem, but research shows its effects are minimal,” Mudge said. “You technically are breaking the barrier – but you’re not affecting it much if any. The benefits of aeration far outweigh the potential loss of weed control.”

For lush, weed-free lawns like this, landscapers have to be proactive and apply pre-emergent herbicides.
Photo: Dow AgroSciences

When customers only see weeds appearing in one specific area of their landscape, they may be tempted to ask you to only spot treat with herbicides. The problem with this, according to Roper, is that the areas left untreated will still risk a potential outbreak of weeds.

“Full coverage will achieve the best results,” Roper said. “It is only a matter of time until weeds will start growing in untreated areas.”

Regardless of what customers may think, all pre-emergents are not created equal. Mudge says that all pre-emergents will have different strengths and weaknesses in regard to what they can and can’t control and how long they will last. Mudge encourages landscapers to know exactly what weeds they’ll be working with to ensure they are able to find the best herbicide option.

The final common myth we’ll touch on is that herbicides alone are really all you need. According to Mudge, herbicides are indeed an invaluable tool when it comes to weed control, but they work best when paired with a sound agronomic approach.

“You can’t just rely on herbicides and forget about agronomy,” Mudge said. “That turf has to be happy, so soil fertility is critical. A lawn with a bad soil pH is never going to grow well and will always have weed issues. At the right pH, you’ll have fewer issues with insects, disease and more. Crop and soil science is a fundamental part of effective plant management.”

In summary, Roper encourages landscapers to always read the labels to know exactly what your product can do; cheapest isn’t always the best if it doesn’t end up working to prevent the weeds in the area.

“If you apply a non-effective product and weeds explode in a customer’s yard, you just wasted not only the cost of that product, the labor involved, but also the cost of a return trip to correct the issue,” Roper said.

Pre-Emergent, Post-Emergent, and Weed & Feed: What’s the difference?

Weeds can haunt even the most meticulously maintained lawn. Luckily, the list of herbicides available for homeowners is extensive. However, that doesn’t mean it’s easy to decipher the difference in products. We’re here to help you differentiate between pre- and post-emergent herbicides and simplify your weed control.

An Herbicide Discussion

Watch the video below to see Super-Sod’s own Shannon Hathaway discuss pre-emergent and post-emergent herbicides in her class titled “Proper Care of Warm Season Lawns.” Shannon answers questions from her pupils and gives recommendations for tackling weeds such as nutsedge and clover.

Pre-Emergent Herbicides

Pre-emergents attack weed seeds before they have a chance to germinate. This means you interrupt the growing process before weeds even become visible. With pre-emergent, you are taking preventative measures.

When to apply pre-emergent herbicides: Pre-emergents are applied in the winter before green-up and in the fall to prevent weed seeds from germinating. However, they’ll be a waste of money after your weeds have already appeared. In a typical year in the Southeast, apply pre-emergent between February 15 and March 1 for summer weed prevention and again between late September and early October for winter weed prevention.

Forsythia is the signal: Want a visual reminder of the best time to apply pre-emergent in winter? Forsythia, a shrub with yellow flowers, is a natural indicator for pre-emergent applications. When you see forsythia beginning to bloom, you know it’s time to tackle weed prevention for the spring.

Treatment Options: Visit your local Super-Sod store to discover the right products to protect your lawn from weeds. For those not near Super-Sod, some products we like are 0-0-7 with Stonewall and Hi Yield. Always check the pre-emergent label to guarantee your grass type is listed and you treat your lawn properly.

Post-Emergent Herbicides

Post-emergent herbicides are instrumental in knocking out those pesky weeds once they’ve surfaced for the spring.

When to apply post-emergent herbicides: When weeds start popping up around your lawn, start searching for post-emergent products for the spring and summer.

How to identify weeds:To identify the type of weed you have, take a picture or a sample and show it to your local Extension agent who can help you identify the culprit. If you would rather turn to technology, you can download the ID Weeds app, available for free download on both Apple and Android devices. This helps you identify the weed by selecting plant characteristics to narrow down the species. To identify weeds common to your stateor geographic region, check out Preen’s Weed ID website or PBI Gordon Corp’s WeedAlert.com. These sites provide herbicide product recommendations, but be sure to shop around and call your local Super-Sod to ensure you purchase an herbicide that’s approved for your grass type.

Treatment options: To treat your lawn, drop by your local Super-Sod for products that will eliminate the weed(s). If you’re not near a Super-Sod, visit a garden center to select a post-emergent herbicide. Wherever you pick up your post-emergent, be sure to read the label carefully and follow instructions. Check the label to confirm the herbicide is safe to use on the type of lawn you have!

Weed and Feed: Herbicide and Fertilizer

We’ve discussed pre-emergents and post-emergents, but we haven’t touched on the elusive “weed and feed” that is so popular for fighting off weeds and helping your lawn simultaneously. Weed and feed products are those that contain both fertilizer and herbicide for your lawn.

Is weed and feed a pre-emergent or a post-emergent? Weed and feed can contain either pre- or post-emergent herbicides. It’s important to read the label to determine which kind your weed and feed contains. If your weed and feed contains pre-emergent herbicides it will likely have “prevent” or “preventative” on the label. This means you should apply it to your lawn in winter or fall, as explained above in the pre-emergent section.

Weed and Feed on Warm Season Lawns (Bermuda, Zoysia, Centipede): If applying a weed and feed to a warm season lawn in the winter or fall, be sure the weed and feed formula you use does not contain any nitrogen. Applying nitrogen to your Bermuda, Zoysia, or Centipede before your lawn has completely greened up or at the end of the growing season while it’s entering dormancy will damage your grass. To check this, make sure the first number in your fertilizer formula is zero (i.e., 0-0-7).

Weed and Feed on Cool Season Lawns (Tall Fescue): It is okay to apply a weed and feed with Nitrogen to tall fescue in spring and fall. Avoid nitrogen on Tall Fescue from June through August.

Staying on Schedule

Now that you know the difference in herbicides, you can keep up with your fertilizer and weed control schedules by finding your grass variety on our Lawn Maintenance Guides and following the recommendations.

If you would like reminders each month about weed control and other lawn maintenance practices, join our Monthly Lawn Tips email list.

Topics: herbicide, How-To, weed control, weed management

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