When the snow melts and the grass starts growing again, so do weeds that can attack your customers’ lawns and lead to costly callbacks. But pre-emergent applications and proper fertilization can help make a lawn the envy of the neighborhood.
Battling annual grass weeds like crabgrass is a constant struggle for lawn care companies throughout the U.S. whether you’re dealing with warm- or cool-season grasses.
Summer annual weeds germinate as the weather gets warmer and a pre-emergent herbicide can stop them in their tracks. Warm weather and wet conditions facilitate crabgrass germination, and spring rains reduce the efficacy of pre-emergent applications.
Crabgrass and many other weeds germinate in the spring, grow throughout the summer and set seed in the fall. While the first hard frost of the fall or winter will destroy many plants, the seeds will pop up again the following year, so a pre-emergent is a good option in the spring to stop crabgrass before it starts. If you haven’t used a pre-emergent, or if the heavy summer rains have thwarted your efforts, post-emergents can save your customers’ lawns.
To find it fast, look in thinner or shorter grass areas since they warm up first, making it easier for crabgrass to take over. Look for plants with coarser and wider textured leaves that are lighter green than the turfgrass, and look for matted areas.
“The color difference is especially pronounced in cool-season lawns,” says Dr. Jim Brosnan, associate professor of turf and ornamental science at the University of Tennessee in Knoxville. “Both smooth and large crabgrasses grow via stolons and thus can form mats within a lawn.”
The earlier you can treat it, the easier it will be to control because as it matures, more applications will be necessary. “Being aware of the growth stage and life cycle is important,” Brosnan says. “The larger plants grow in size, the harder they become to control.”
But beware that removing a mat of crabgrass will leave a bare spot in the lawn where other weeds will invade. “Once plants are removed, something needs to be done to introduce plant competition in these bare areas,” Brosnan says. “This is particularly true with annual weed species like crabgrass that produce an abundance of seed.”
In the Northeast, some common weeds are henbit, chickweed, deadnettle, annual bluegrass and wild mustards. “I call winter annuals the forgotten lifecycle because in the fall, people are praying for the end – and there are weeds there, but at that point, it’s time for fall cleanup and fertilization,” says Randall Prostak, University of Massachusetts Extension weed specialist.
In the Southeast, henbit, chickweed, dandelion and Carolina geranium crop up early in the year.
“Applications in January and February will serve you well moving into the middle and latter part of spring,” says Clint Waltz, turfgrass specialist at University of Georgia.
Northern states in the Midwest region may better relate to weed pressures experienced to the Northeast, while closer to the transition zone in Kansas, spring’s “entrance” can vary up to six weeks and has a significant impact on what turf and ornamental issues LCOs will experience.
During the first quarter, warm-season turfgrass can use a “winter weed cleanup” with a non-selective glyphosate to treat winter annual broadleaf weeds. It’s safe because the grass is dormant, says Jared Hoyle, extension turfgrass specialist at Kansas State Research and Extension.
Dry conditions in the West can drive plants into “stress mode,” says James Baird, turfgrass specialist at University of California Riverside.
It also affects the efficacy of herbicides since the chemicals must be absorbed up into the weed. Dust can also be a factor when it coats the plant. The University of California’s Division of Agricultural and Natural Resources says it may be worthwhile to water lawns a few days before making an application to make sure weeds are actually growing.
“Applications in January and February will serve you well moving into the middle and latter part of spring.” Clint Waltz, turfgrass specialist, University of Georgia
For a faster green-up in the spring and healthy plants that can withstand weed and pest pressure, fertilizer applications are key. Key times to fertilize are early spring, late spring and late summer or early fall to promote root growth that will keep grasses strong.
Knowing what’s under the grass is the key to figuring out how much fertilizer to apply and when to do it. While you can check the pH of soil without conducting a full test, there’s no other way to find out how much phosphorus or potassium are in the soil.
Typically, when doing soil testing, Jeff Carroll, owner of Jefferson Sustainable Landscape Management in Woodinville, Washington, finds that the soil has way too much nitrogen as a result of over fertilizing.
Nitrogen will give you a nice, green lawn, but not long-term plant health, so it’s important to look at pH and other nutrients, he says.
And it’s not just the existing nutrients that dictate the schedule. Sandy soil leaches fertilizer faster than clay. “There aren’t as many nutrients in (sandy) soil so it will need more fertilizer applications each year closer together,” says Henry Velez, enhancement manager at Green Acres Landscape in Salem, Oregon.
Tyron Jones, president of Deans Pest Control in Fruitland Park, Florida, conducts numerous soil samples when enrolling new clients in a program. “We have done hundreds of soil samples over the years, and if I was starting a brand-new company, I’d run out and do 50 to 100 soil samples to get a good idea of what you’re working with on your lawns,” he says.