Now is the time for lawn care operators to control fall weeds before they take root.

Autumn is approaching, which means those pesky fall weeds will soon be sprouting. And for many lawn care operators, autumn also means time for client contract renewals, so it’s a good idea to put a stop to the wild carrot, thistle, dandelions and other turf invaders before they take root.

“You’re often judged on the lawn and how good it looks based on the weeds,” said Chris Lemcke, national technical director of Weed Man U.S.A. in Oshawa, Ontario. “With contract renewals in the fall, it’s important to make sure your lawns look good.”

Cool-season turfgrass markets in the upper Midwest and the Northeast received an abundance of rain this spring and summer. Matt Cavanaugh, a research scientist from the University of Minnesota, says these rainy conditions may result in more weeds than usual this fall.

Fall also triggers perennial weeds to start moving carbohydrates to the roots to survive the winter and to have energy to begin growing again in the spring, which Cavanaugh says is an effective, natural tool for lawn care operators (LCOs) to utilize.

“These actively-growing plants pull systemic herbicides into the root system with the movement of carbohydrates, providing greater weed control than other times of the year,” he said. “If you can only do weed control for perennial weeds one time during the year, always make it during the fall.”

In the West and the Pacific Northwest, spring and summer were very dry. Lemcke says dry conditions can make weeds harder to control because plants close their stomata and develop a hard, waxy cuticle to retain moisture, making it more difficult for the herbicide to soak into the plant. Lemcke adds that LCOs also have to be careful when using herbicides and other products when it is hotter than 90 degrees, because a blanket treatment can weaken a lawn. He recommends performing spot treatments in late summer and early fall to stay on top of the weeds before they become an issue.

“The important thing is to have your employees trained to treat the weeds as they arise,” Lemcke said. “Right now we are spot treating to make sure the guys are on top of it.”

Warm-season turfgrass markets also saw more rainfall this spring and summer, which can make weeds such as dollarweed and sedges more prominent, said Anita Alexander, a field research scientist for Dow AgroSciences Turf & Ornamental. But she says the biggest threat to warm-season turf this fall is Poa annua, or annual bluegrass. Several states have documented an herbicide-resistant form of the weed, she adds. The resistance is caused by overuse of the same treatments without rotating chemicals.

“If the same modes of action are used in the coming year, the issue will continue to worsen and control of Poa annua in turfgrass settings will be more problematic,” she said.

Preventing fall weeds

Most LCOs agree that maintaining a thick, healthy lawn throughout the year is the best way to combat fall weeds, and educating the homeowner on how to properly care for their lawn between treatments also can help keep weeds at bay. For example, mowing the lawn at its recommended height will allow the turf to have longer roots that can more easily reach underground water supplies and absorb more sunlight. Raking fallen leaves on a weekly basis will prevent the leaves from smothering the grass. September is also the time of year LCOs should recommend their clients receive aeration and over-seeding services using improved varieties to turfgrass that require less water and are more disease tolerant.

“The thicker and healthier the plant, the fewer the weeds,” Lemcke said.

Proper fertilization is also important for maintaining a healthy lawn, said Jamie Breuninger, technical leader at Dow AgroSciences Turf & Ornamental. Fall fertilization will allow cool-season grasses to spread and thicken, resulting in less room for weeds to thrive. For example, fertilizing in the fall is an effective way to manage crabgrass in the spring, Breuninger said, as crabgrass needs light to germinate and dense turf means less light at the soil surface and less room for the annual grasses to take hold.

“Fall fertilization will allow the cool-season grass to spread,” he said. “As the grass thickens, there is less room for the weeds to take over.”

Fertilization is also beneficial for warm-season lawns.

“Fall fertilization can improve the turfgrass health going into winter and allow it to overcome disease pressure and winter damage,” Alexander said. “Fertilizers should be applied in early fall before the warm-season grasses go into winter dormancy.”

Aaron Hathaway, a research assistant at Michigan State University’s Department of Plants, Soil & Microbial Sciences, says it’s a good idea for LCOs to communicate to their clients how fall herbicide applications work. With spring herbicide treatments, homeowners are used to seeing the “curling, twisting, pleasing sight” of dying weeds because the product moves to the new growth above ground. Herbicides applied in the fall move mostly below ground, so homeowners see less of “these torturous signs of the looming death to come.”

“Prepare clients with an understanding of why fall-timed herbicide applications are better and what to expect,” Hathaway said. “They can expect more bang for their buck and a healthy, relatively weed-free lawn in the spring.”

Cavanaugh agrees that client communication is key.

“Communication of current weather conditions and how they relate to lawn care will always go a long way,” he said. “Being informative to your customers will go a long way in developing a loyal customer base.”