PESTICIDES/FERTILIZERS: Postemergent Refresher Course

To the average homeowner, a weed is a weed, and if it’s in their yard, it must be killed fast. But lawn care operators (LCOs) know that weeds must be controlled during the times when they’re actively growing in order for the herbicide to move through the plant.

“The most important thing in order to kill a weed with postemergent products, is that it needs to be growing actively,” says Kyle Miller, senior technical specialist, BASF Turf & Ornamental, Richmond, Va. “You want to make sure you’re not putting the herbicide on too early in the spring when it’s not growing yet and can’t move the product very effectively. The same thing is true later in the summer months when plants may be experiencing heat or drought stress. Herbicides may not be particularly effective at these times.”

Mike Pender agrees, noting the importance of getting to the weeds before their “old and tough.” Of course, this may require some extra education for customers who want weeds gone as soon as possible. “Communication is key with customers,” says the owner of Classic Gardens, Birmingham, Ala. “We try to explain to customers that if they have weeds, it’s probably taken a few years for their lawns to become infested and that if they give us the next 12 to 18 months, we can get that turned around for them, but thinking it will take 30 to 90 days is unrealistic.”

Instead, most lawn care companies make a number of visits to their clients’ properties annually, treating for weeds each time. For northern climates, six to eight visits over the course of a year is normal, while Pender works year-round, visiting clients 12 times a year. Regardless of the location, making multiple visits allows LCOs the chance to control multiple types of weeds that may crop up in a given lawn during the course of a season. “We’re going after different weeds at different times of the year,” explains Rob Palmer, owner, Weed Pro, Sheffield Village, Ohio. “Depending on the time of year and the weeds that we’re dealing with, we’ll tank mix different herbicides to get the right control.”

Being in a cooler climate, Palmer and most other LCOs have to consider an important cue that will let them know when weeds are actively growing – soil temperature. “Some people use outside temperature as an indicator for when to apply postemergent products, but that’s not always accurate,” says Doug Obermann, turf and ornamental product manager for PBI/Gordon, Kansas City, Mo. “It may be 70 degrees outside, but the weeds aren’t growing because the soil is still cold. In those conditions, postemergents won’t be as effective.”

The University of Illinois Extension Service offers some typical weed germination timing by soil temperature, including crabgrass – seven to 10 consecutive days of soil temperatures between 55 and 60 degrees Fahrenheit; goosegrass – soil temperatures above 65 degrees Fahrenheit for several weeks; and yellow foxtail – soil temperatures of 68 to 92 degrees Fahrenheit.

DON’T DOUSE. Once LCOs know their target weeds are growing, it’s time to attack – but don’t go overboard, professionals say. “Especially with spot treatments, there’s a tendency to soak the weed with herbicide, but you really just need a little bit to do the job,” says Harold Enger, assistant director of franchise support, Spring-Green, Plainfield, Ill. “There’s a perception that if a little is good, a lot is better, but putting too much herbicide down will force the weed to go into shock right away and stop absorbing anything. You may even see the grass around it die, but the weed stay alive.”

For spot spraying just a few weeds in a lawn, most LCOs will use a backpack sprayer that should be accurately calibrated to get the right application rate. To do this, PBI/Gordon offers the following tips:

1. Fill the sprayer with water.
2. Spray into a measured container for one minute, keeping the pressure constant.
3. Measure the amount of water dispensed to determine the appropriate mixing rate for correct application:
• If the spray volume is 1 gallon per minute, use a mid-to-high range of the dosage recommended on the product label per gallon of water.
• If the spray volume is less than 1 gallon per minute, use a low-to-mid range label dosage per gallon of water.
• If the spray volume is greater than 1 gallon per minute, use the high-range label dosage per gallon of water.
4. Spray as you would for broadcast applications without drenching the weeds.

Calibration of large tanks can be done similarly and is equally important. PBI/Gordon says tanks should be calibrated at least weekly to ensure proper application. Enger says daily is even better and to monitor material use throughout a day’s worth of applications. “If you’re supposed to be spraying 3 gallons per 1,000 square feet and you’ve done 40,000 square feet, you should have put down 120 gallons,” he says. “Check your progress throughout the day and adjust your pressure or flow as necessary.”

Palmer says his company always makes sure sprayers are accurately calibrated and also provides technicians with just the right amount of material to take care of the jobs they have for a given day. This prevents both over- and underapplication. “Application and calibration rates are really important and we make any adjustments necessary to make sure those rates are always in line,” he says. “Our applicators are ultimately responsible for weed control on the lawns they care for, so we take out as many variables as possible to ensure those applications are effective. For instance, we try to take out the possibility of mixing improperly by only mixing enough material for the amount of work they have to do. The technician may come back with a few gallons left over because he or she didn’t have to treat for as many weeds as we expected, but that technician also has to answer to the production manager if the weeds aren’t effectively controlled but they had material left over.”

At Weed Pro, technicians make daily calculations of the total square footage of turf they’ll be treating and fill their tanks with the appropriate amount of application material, Palmer explains. “If they’re making a full broadcast application on Mr. Smith’s yard and just spot spraying on a few lawns, they’ll add up the total square footage, which could be around 200,000 square feet,” he says. “At an average rate of 1 gallon per 1,000 square feet, they know they’ll need 200 gallons for the day and they may add some extra in there in case they have new lawns on their routes. We don’t want the technicians to overapply and waste product, but we also don’t want to have leftover material that can’t be saved.”

Proper application techniques also ensure that material isn’t wasted or inadvertently overapplied. Unlike fertilizer applications that may need a bit of overlap in application, Obermann notes that overlapping spray passes for broadcast applications of postemergent herbicides should run “pattern to pattern” without overlapping. “You don’t want to overlap because you’re doubling the label rate,” he says. “Another detail to remember is the motion you need to use when putting the material down. With flat nozzles on backpack sprayers, a swinging arc motion can result in the worst application uniformity possible – almost like a zigzag that misses a lot of turf area. Backpacks are really designed for spot treating.”

Palmer and other LCOs add that their technicians spend a week to a month before the lawn care season begins, practicing the correct spray patterns of lining up each pass of a hose with the previous one. One way to do this effectively, Palmer says, is to have technicians use spray equipment filled with clean water and make “applications” to asphalt. Technicians are able to see where the water goes down and get used to lining up their passes to eliminate overlap.

POSTEMERGENT PRICING. Despite the fact that many postemergent herbicide applications are made on an as-need basis with spot-spraying, most lawn care companies include the cost of these applications in their basic prices for lawn care packages. “For a 5,000-square-foot lawn, we charge $43 for an application that includes all fertilizers, preemergents, postemergents, lime and gypsum once a year,” Pender says, noting that the longer growing season in the south allows him to be on properties once a month and keep an eye out for potential problems. “We put down preemergents six times a year, which gives us a good chemical barrier, but with postemergents also included in our price we’re able to spot treat with those as the situations arise.”

Pender and other LCOs agree that postemergent products are among the least expensive items in an application, including everything from fertilizers and other materials to the cost of labor and insurance. Prices for most postemergents usually range from 10 cents to 75 cents per 1,000 square feet. Moreover, as a lawn care company has a period of months or years to take care of a given lawn, broadleaf weed pressure usually lessens overtime. Thus, companies may use lower postemergent herbicide rates per visit over time.

“We find that any customer who’s been on our program for a full year has fewer weeds over time, so postemergent blanket spraying isn’t necessary,” Palmer says. “My technicians and I are on a lawn every 32 days, so we’ll see the weeds and spot spray as needed. Also, our customers know that if they have weeds between applications, if it’s close enough to the next application we’ll treat for it then, rather than making an additional visit.”

In order to give his customers the best weed control possible, Palmer says as much as 20 percent of his materials budget is wrapped up in postemergent and preemergent herbicides. “I spend more on weed control than most companies,” he says. “With a name like Weed Pro, our weed control has to be effective, so we’re prepared to spray every time we’re on a lawn and we have the materials on hand to accommodate that.” Palmer’s herbicide budget also includes products that manage weed control in landscape beds (see And So To Beds on page 97), which can be more expensive than similar products used for turf. To cover the costs, Weed Pro charges a $30 minimum for the first 3,000 square feet of turf per application, plus $4 for each additional 1,000 square feet.

Pender says remembering that there will always be weeds is something LCOs should explain to their customers, while still making the commitment to work on eliminating the weeds that create the biggest nuisance. “You’ll never get rid of all the weeds, but we try to work at them even if they seem to be uncontrollable,” he says. “We’re on their yards once a month and we let our customers know we’ll spend the extra time we need to in order to keep their lawns looking great.”