PESTICIDES AND FERTILIZERS: Productive Preemergents

Its flat, broad blue-green leaves are a blemish against the supple turfgrass, like a pimple on a beauty queen’s face.
 
A complaint is placed with the lawn care operator: “How could this happen in my lawn when I paid for a preemergent herbicide program?”
 
It’s an all too common question, LCOs say. Crabgrass and other broadleaf pests are opportunistic, waiting for the right combination of light, moisture and soil temperature to spring forth and wreak havoc. Preemergent herbicides are designed to stop weed growth before it begins, so a spring preemergent program is the most effective way to combat these weeds. However, broadleaf interlopers will still appear. It’s just a fact. Knowing the reasons behind why these weeds flare up and passing this information along to lawn care clients set realistic expectations about a preemergent herbicide program.

TOTAL ERADICATION. The most common client misconception LCOs face is the belief that one application means no more weeds, ever.
 
“They expect it to work on every weed known to man when the preemergent primarily targets crabgrass, some broadleaf and a few grasses,” says Dave DeLuca, president of DeLuca Brothers in Terryville, Conn.
 
“I run into this topic every single spring,” adds Richard Carter, proprietor of My Lawn Guy, Andover, Mass. “I am always happy to sit down with a customer and set the record straight.”
 
Despite some misleading advertising offering the “weed-free lawn,” LCOs need to establish expectations with clients that no product provides total control, says Mark Urbanowski, senior product manager at Dow AgroSciences in Indianapolis. Rather, the realistic outlook for “acceptable” control that an LCO should convey to the client is anywhere from 85 percent to 98 percent weed control, he says.
 
“It’s critical for applicators and end users to understand that no preemergent product gives 100 percent control,” Urbanowski says. “It just doesn’t happen. But by studying labels and local research, LCOs can do a lot to deliver the best control possible.”
 
An acceptable level of control is possible if an LCO is vigilant about his application timing and rate and informs the client on proper maintenance.
 
Timing is critical, LCOs say. Preemergent products should be applied before the soil temperature reaches between 53 to 58 degees F at the four-inch depth, the threshold for crabgrass germination. Waiting for the forsythia to bloom, one of many common myths, is irrelevant because it doesn’t account for soil temperature.
 
“In our region, many customers think the product needs to be applied before April 15,” says Patrick Bucklin, owner of Atlantic Turf Care in Falmouth, Maine. “We try to explain that the product lasts for 90 to 120 days and if applied too early the control will run out prematurely.”
 
Application rate is another key for a successful preemergent program. Product labels offer a wide range of rates that address various geographic and environmental differences, and it’s important for an LCO to understand the rate he should use for the best weed control in his region.
 
Proper mowing practices following a preemergent application also improve weed control, says Harold Enger, director of training and franchise support at Spring-Green Lawn Care in Naperville, Ill. “If you mow at a higher setting from spring through summer the client will have less of a problem with crabgrass,” he says. “Mowing high keeps the sun from heating up the seeds and getting them to germinate.” Enger adds Northern turfgrass should be kept at a high of between 2 ½ to 3 inches in height, and Southern turfgrass from 2 ½ inches and as high as 3 ½ inches for tall fescue.

WASHED AWAY. Another misconception is that rain following an application washes away the preemergent agent, says Brad Johnson, president of Lawn America in Tulsa, Okla. “Rain will actually help in most cases as preemergents need to be watered into the soil within a few days,” he says. “If the homeowner doesn’t water the product, many common preemergents will breakdown from sunlight and loose some of their effectiveness. So the sooner we can get the products watered into the soil the better.”
 
The oil-based material needs water to spread, Enger says. It’s important during a dry spring for LCOs to advise clients to water following a preemergent application and that there is little to no risk it will wash away.
 
“Once the product is washed in it’s pretty much rain fast,” says Ben Cicora, business manager for herbicides at Bayer Environmental Science, Raleigh, N.C. “It’s designed to stay put.”

RAKING. DeLuca had weed breakthrough on seven of 10 lawns in a neighborhood he serviced one year. He learned later the problem wasn’t product failure or LCO error, rather the culprit was misguided maintenance. “It turned out that two weeks after I did my applications the lawns were power raked,” he says. “Pretty much obliterated the barrier.”
 
Vigorous soil disturbance will break down the preemergent barrier. “A light hand raking will not disturb the preemergent barrier,” Enger says. “But running a power rake will destroy it.”

BREAK THROUGH. A thick, well fertilized, properly maintained lawn will have less of a problem with crabgrass. However, many lawns are far from perfect. Broadleaf seeds will find opportunities to germinate along  high-traffic areas, patchy bare spots and stretches along curbs, driveways and sidewalks damaged by winter rock salt use.
 
Many LCOs hit the outbreak with a reliable postemergent product. “We only apply this when there has been crabgrass that has germinated and a customer has called about it,” says David Williams, president of Williams Lawn Care in Lancaster, N.Y. “We don’t charge for crabgrass control failures. In any case I try not to shift the blame but rather explain the reason for the failure and then tell the client I will fix it. I’ll use a postemergent product and then check it in a week.” 

Ultimately, a preemergent program is one phase of a season-long regimen for a healthy lawn, says Ken Reis, owner of Turf & Shrub Management in South Dartmouth, Mass. “Think of the service as one leg of a three-legged stool,” he says. “Any sturdy three-legged stool will support you if you sit on it. But if one of those legs fails, you can no longer sit on the stool. The preemergent program is one leg of that stool, with mowing as another and watering as the third.”