If left untreated, winter weeds can create big problems for lawn care operators come spring.

Don’t let the colder temperatures fool you. Weeds can be just as big of a problem in the winter as they are any other time of the year. If left untreated, these weeds will likely flower with a vengeance come spring, stealing nutrients from healthy turf. That’s why lawn care experts recommend identifying and treating them before the winter weather sets in.

“Customers may not see a problem now, but if not treated in the fall, these weeds are very likely to be visible next spring when warmer temperatures occur and the weeds go into the flowering stage,” says Jamie Breuninger, technical leader for Dow AgroSciences Turf & Ornamental. “Late fall and early winter are quiet periods for a lot of weeds, as they will stay green until a heavy frost or freeze pushes them into dormancy. That’s when the weeds are building energy reserves for spring growth.”

Why Winter Weeds?

Turf grass experts agree that winter weeds are more prevalent in lawns with thin turf, or turf that has been damaged from drought, insects or lack of sunlight. They are also more likely to invade lawns that were not seeded in the fall. Greg Breeden, turf grass weed science extension specialist at the University of Tennessee, suggests lawn care operators try to repair any bare, worn or thin areas before applying an herbicide for better long-term control.

“For all weeds, it’s really good to have a dense stand of turf,” he says. “If you are managing your turf to be as healthy and competitive as it can be, that will go a long way.”

For several different reasons, Breeden says, winter weeds often go unnoticed until they’re mature and flowering. For example, homeowners spend less time outside, the ground is often covered with leaves or snow, and winter weeds tend to stay small in the turf canopy until they mature in the spring. It’s common to first spot winter weeds in plant beds, he adds. Careful monitoring will help LCOs identify winter weeds and establish timely, proactive control methods that will make their lives easier—and their customers happier—come spring.

“The key is to know your areas and continue to scout them,” Breeden says. “Hopefully lawn care operators have been managing the areas they noticed weeds in last year and have already came up with a control plan for this year.”

Weed ID

In the north, common perennial weeds include clover, dandelion, plantains and ground ivy. Common northern winter annual weeds include henbit, common chickweed and shepherd’s purse. In the south, Poa annua, or annual bluegrass, is the most common winter grassy weed, and common broadleaf varieties include bittercress, purple deadnettle and creeping speedwell. Breuninger says that some winter weeds can be challenging to identify, particularly if they have been mowed or are in a compact rosette stage, but many winter weeds can be identified by their characteristics. For example, henbit has a square stem. Chickweed has a bright, shiny leaf that’s rounded and tapered to a point. Shepherd’s purse has triangular, purse-like pods. There are also numerous websites and journals that can help with weed identification.

“Winter weeds should be identified like other weeds,” says Anita Alexander, field research scientist for Dow AgroSciences Turf & Ornamental. “Look for distinguishing factors of the plant and note climatic conditions around the time the plant germinated.”

Winter annuals, such as common chickweed or henbit, establish from seed in the late summer or fall, flower in early to mid-spring, and die off in early summer. Winter perennials, such as clover and dandelion, can live more than two years and can spread by seed or vegetative plant part. These weeds can overwinter in a vegetative state and flower in the spring but can also survive in the summer or come back from vegetative plant parts or seed produced during spring flowering. With many parts of the country experiencing higher than average rainfall, Breeden expects winter annuals to thrive this year. He adds that the appearance of annual bluegrass has been ahead of schedule.

Under Control

Post-emergent treatments are the most common way to control winter weeds in both cool- and warm-season lawns. By treating winter weeds in the fall when the plants are actively growing, the product will translocate to its roots as well as its shoots, so Alexander and Breuninger recommend ester-based herbicides that are effective in cooler conditions, as amines may not work as well in colder temperatures. In northern states, November is often the last chance to control these weeds until spring because of inclement weather.

“Spring weed control applications can be challenging due to inconsistent weather,” says Breuninger. “Fall tends to be more predictable and the weeds are easier to control because the herbicides translocate better to give more complete control if the weed is actively growing.”

Rodney St. John, an agronomist at Ryan Lawn & Tree in Overland Park, Kan., agrees. “Winter weeds are easier to control in the fall, when they are young and small, than in the spring when they are flowering and fully mature,” he says. “As soon as you see them, that’s when I would get them under control.”
Leaving winter weeds untreated can result in “angry customers, first and foremost,” says St. John. Winter weeds also can weaken the turf stand and compete with turf for nutrients in the spring. When left uncontrolled and allowed to set seed, the weed pressure will only continue to increase.

“You’re the lawn care provider and customers won’t tolerate a lot of weeds in their yard,” St. John says. “From a customer service perspective, I wouldn’t want to leave them hanging around.

“My first recommendation is to have thick, healthy turf,” he adds. “Getting it thick, seeding it, fertilizing it, and mowing it properly will help reduce winter weeds.”