Winning the Ground Game with Pre-Emergent Controls
In the landscape business, as in football, your ground game is the backbone of your offense. In the NFL, teams that boast a seamless offensive line, an explosive tailback and the finest downfield blocking money can buy still struggle to get the ball moving on the ground. In the landscape business, companies with a legion of field workers, gallons of chemical herbicide and razor’s edge equipment still can watch their customers’ emerald green lawns succumb to infestations of weeds.
To be successful, both businesses need someone who knows how and when to deploy each of his weapons —someone to construct and manage a well-adapted game plan for taking control of the ground. In football, they call that someone the offensive coordinator. In the landscape business they call him a contractor.
Weeds come at you from all angles, in all seasons—rain or shine, sleet or snow. They compete with grass for precious sunlight and soil nutrients, and they are resilient. Your goal is to control their advance. Improper weed control irks customers, damaging your professional reputation and leading to a potential loss of business. Fortunately, there are tried and true weapons in your offensive arsenal. Landscape professionals can and do win the ground game against weeds. All it takes is a little proper, prior planning.
Herbicides: your offensive line
The most effective way to curtail weeds is to block them before they’ve had a chance to sprout. Preemergent controls attack weeds while they’re still seeds—essentially eliminating unwanted plants before they begin to germinate. A typical pre-emergent control program incorporates chemical or organic herbicides that create a seal over the top soil. That seal acts as a weed-prevention barrier zone. When employed correctly and in a timely fashion, pre-emergent herbicides penetrate one to two inches of topsoil and prevent the weeds from reaching the surface.
Even while dormant, weed seeds remain viable in the ground for a very long time. “There have been lots of studies done where they’ve excavated seeds in the soil and they can still germinate,” says Mark Urbanowski, senior marketing specialist for Dow Agro-Sciences, Indianapolis, Indiana. “The seeds can stay underground for hundreds and hundreds of years.”
Faced with such a tenacious opponent, you can’t just apply a pre-emergent herbicide once and expect a pristine lawn to maintain its gleam in perpetuity. You need a calculated, annual or semi-annual approach to control.
Dollar-for-dollar, herbicides are the best weapon available in the pre-emergent ground game. For this reason, they remain the status quo in the industry. In the U.S., the chemicals pendimethalin, oryzalin, dithiopyr, prodiamine and siduron are the most common active herbicides used in pre-emergent controls.
When purchasing any turf treatment, be sure to peruse the label.
Chemical concentrations and product ingredients, even within a specific brand, have a tendency to change over time. Keep in mind that not all chemical herbicides are created equal; you need to take explicit care in deploying the appropriate chemical for your specific weed threat.
Weeds are commonly divided into four subgroups: grassy, broadleaf, summer and fall. The taxonomy of the weeds threatening your swath of turf weighs heavily on the relative efficacy of each herbicide, while seasonal distribution determines the timing and size of your application window.
Geography is another complicating factor. Soil temperature is the environmental signal for most weeds to begin sprouting. Due to variations in climate, different species of weed germinate at different times in different regions of the country. Pre-emergent application dates will vary, depending on the weed species common to your market.
When the time comes to formulate your pre-emergent game plan, intimate knowledge of the weeds that grow in your region and the seasons in which they germinate is an invaluable asset. With that knowledge in hand, you can purchase the appropriate herbicide for your project and turn your attention towards strategies for application.
Application: executing the playbook
Timing is everything. As the name implies, pre-emergent controls must be applied before the weeds begin to germinate to have any herbicidal effect. A common myth in the landscape business is that pre-emergent application should be timed to other events, such as the blooming of forsythias or daffodils. This misunderstanding results in thousands of wasted dollars every year and the unnecessary pollution of soils and nearby groundwater.
Jump the gun in the application of pre-emergent controls, and the herbicides are likely to take out more grass than weeds. Apply too late, and weed germination will neutralize any herbicidal effect. What you’re left with is a small window for effective application that opens but twice a year: once for fall weeds and once for summer weeds.
A good rule of thumb is to circle the dates March 15 and September 15 on your calendar, if you’re working in the colder climates. In the Sunbelt states and some areas in the West, you should circle January 30. Those are the dates that should anchor your analysis of when to apply pre-emergent herbicides. Remember that the key indicator in weed germination is soil temperature. You can’t just make this call by the numbers; you need to account for Mother Nature. In the event of an unusually mild spring, you may have to move your application date by a few days.
“Dates are fine, in general,” says Ken Klopp of LebanonTurf, Lebanon, Pennsylvania. “But climate conditions vary year by year, so it is important that applications of pre-emergent herbicide products be coordinated with soil temperatures and the type of weed, rather than just the date.”
For better precision, take the soil’s temperature. Summer weeds, in general, germinate once soil temperature reaches 50 degrees Fahrenheit. But there are no bright line rules in weed control, only general guidelines. Goosegrass, for example, germinates when soil temperatures reach 60 degrees Fahrenheit for three consecutive days. If you begin applying your pre-emergent controls when the soil reaches 50 degrees, and the ground temperature doesn’t crack 60 for another month, goosegrass is likely to emerge. For reasons like this one, you can’t overestimate the value of knowing exactly which weeds threaten your jobsites.
Once you’ve determined which weeds need to be controlled and when the treatment needs to begin, you can start mixing your herbicide. Pre-packaged pre-emergent products contain only trace amounts of active herbicide, making them an expensive and inefficient option for the landscape professional. A more economic approach is to purchase the chemicals in bulk and mix them with water until you achieve the appropriate spray concentration.
It is also important to note that pre-emergent controls must be watered into the ground after application. The watering process is integral to the formation of the weed-prevention barrier throughout the topsoil. Plan to water in your herbicide five to seven days prior to the anticipated weed germination date, so that the herbicidal barrier has time to settle.
After the barrier has settled, be careful not to take any action that runs the risk of penetrating the nascent shield. Aerating or otherwise puncturing the soil will create points of weakness in the weed-prevention zone. Aggressive and opportunistic weeds can detect these chinks in your armor and grow out through the aerated points.
The one bright spot in this morass of variable application dates and unpredictability is the relative consistency of problem locations. Savvy landscape professionals scout out their properties months beforehand, noting any weed-prone locations. If you identify the areas where weeds are likely to emerge, you can limit your application of herbicide to just those threatened plots and avoid saturating an entire yard.
Limiting the range of application is good business and good PR. even though the vast majority of chemical herbicides pose no health risk to animals or humans, some customers may still be skeptical of having their entire property saturated in weed killer. “There are negative preconceptions that go with chemical herbicides,” says Mike Sisti, marketing manager for Lebanon Seaboard Corporation, Lebanon, Pennsylvania.
“But that’s just not the case. When performed by a trained professional, they can really complement a smart ergonomic program.”
Sometimes these assurances won’t always be enough. Some of your clients won’t like the idea of using these chemicals. In addition, if you’re offering “green” service, chemical herbicides are out. For the organic-minded customer, there is another play.
Corn gluten meal: the organic option play
In 1985, Dr. Nick Christians, working out of Iowa State university, discovered that corn gluten meal displayed significant herbicidal effects when applied to otherwise un-treated turfgrass prior to weed emergence. Since Dr. Christians’ experiments in the ’80s, corn gluten meal (CGM) has become the primary option for organic pre-emergent weed control. A byproduct of corn used to feed livestock, CGM is 100percent nontoxic and a more effective pre-emergent control than standard mulch.
The nitrogen released by CGM is only effective against small-seeded annual and perennial weeds. It is commonly used in lawns, gardens and fields by private consumers. Landscape professionals tend to avoid CGM, due to its high cost, relative to chemical herbicides.
A good practice for your company might be to present the costs of the two weed control options side-by-side to your clients, and let them make the final decision. Property owners overly concerned with the spraying of chemicals on their lawns and gardens should be willing to pay the heftier fees for CGM.
You can apply CGM with a spreader or by hand in the early spring and fall. Overseeded lawns require CGM application at least six weeks before sowing or two weeks afterwards, so that the nitrogen released by the corn gluten doesn’t interfere with the growth of desired grasses.
Responsibility for the ground game ultimately falls on you. Know your opponents and tailor your game plan and you’ll be sure to walk away from the field with a win.