Get the upper hand on crabgrass this spring with these sound tips.

Spring has sprung, and that means it’s time for lawn care operators (LCOs) to go into attack mode against weeds before they emerge. There are a slew of problematic spring weeds, like dandelions and clover, but perhaps no springtime weed is peskier than crabgrass. But take heart, LCOs. With sound application and thorough preparation, you can get control of your nemesis crabgrass, and keep it.

Time applications wisely

Crabgrass germinates when soil temperatures reach 55 degrees F, so it’s crucial that LCOs apply their preemergent products before then, says Anita Alexander, U.S. Field Research Scientist 
for Dow AgroSciences in Lawrenceville, Ga. She adds that it’s best to select a product that’s also labeled for goosegrass and broadleaf weed control, for the best control and higher customer satisfaction.

Corey Pangborn, technical services specialist, Scotts LawnService, says timing is probably the “single-most important factor” when it comes to the success of the preemergent application. So once soil temperatures hit 55 degrees, applicators better get busy. Pangborn recommends investing in a soil thermometer and using local resources like growing-degree day trackers or soil temperature stations.

“Most applicators know that when the forsythia blooms, they need to get a move-on, and if the dogwood blooms while you’re nowhere close to finishing your preemergent applications, you’re in trouble,” he says.

At The Ohio State University, where Dave Gardner is associate professor of turfgrass science, forsythia blooms in early to mid-April. It blooms earlier as you move south, and later as you go north, he says. To save money, applicators don’t necessarily need to apply preemergents to the entire site, he says, but rather, just to areas known to have previous crabgrass infestations.

In the South, where the growing season is long, LCOs likely will need to make a second application of a preemergent product six to eight weeks after the first for better control, Alexander cautions.

But simply applying a preemergent product isn’t enough. It also needs to be activated. Otherwise, it won’t be effective. “After application, rainfall or irrigation need to be applied to disperse and move the pesticide down to the soil surface,” Gardner says.

Alexander recommends irrigating 24 to 48 hours after the preemergent has been applied. “It’s important to educate the clientele about the importance of this, because the quicker the herbicide gets into the soil, the quicker it’s providing that barrier to weeds and the more bang for their application buck,” she says. “It’s activated by irrigating with at least 0.25 to 0.5 inch of irrigation or rain.”

Wise cultural practices

But lawn care operators can’t rely on products alone to control preemergent weeds. Sound techniques such as proper fertilization and mowing are important, too, And no cultural practice is more important than proper mowing when it comes to controlling crabgrass, says Pangborn.

“If the lawn is being cut too low or is being allowed to get too tall between mowings, this weakens the grass and gives crabgrass seeds the sunlight they need to germinate,” he warns.

Most LCOs also fertilize when they make their preemergent application in the spring, Pangborn says. Doing so, he says, “encourages growth of the desirable lawn grasses, which will in turn shade the soil and prevent crabgrass germination.”

If using a granular fertilizer, Alexander says, a broadcast spreader is better than a drop spreader for uniform distribution.

While fertilization and mowing play important roles this time of year, LCOs shouldn’t ignore the importance of spring aerifying, Alexander says. “When you’re coming out of winter there will be bare spots and areas where rain and snow have beaten down your grass, so aerification is another important practice, especially if you have thatch buildup,” she says.

But watch the timing of the overseeding, she says. LCOs shouldn’t overseed right after they’ve applied a preemergent. Rather, she says, “aerify, overseed and let the turfgrass get good root establishment” before applying a preemergent.

But even the best lawn care operators can’t do it all. That’s why it’s so important for lawn care operators to educate their clients on wise lawn care methods.

“I always like to tell people that educating their clientele is one of the best things they can do,” Alexander says. “Educate them about irrigation to activate the herbicide, never mowing off more than one-third of the height of the turf, and use deep, infrequent irrigation to alleviate stress. Unless the LCO is managing that site from beginning to end, they don’t have the ability to police what the homeowner is going to do, but they can educate them with a flier or a door hanger.”

In the end, Alexander says, the best weed control is quite simply healthy turf. “Whatever you can do to get your turfgrass healthy, green and stress free will enable you to outcompete most weeds,” she says.