Annual Battle Against Crabgrass is Underway

Crabgrass in an annual weed that grows best in hot, dry conditions. A spate of hot weather in late June has been a boon to crabgrass, said Kevin Frank, a professor of crop and soil sciences at Michigan State University.

The Heat is On

Areas of the lawn that receive radiant heat from sidewalks, driveways and structures are most prone for crabgrass. Several species thrive in the U.S. with the most common being large crabgrass, smooth crabgrass and southern crabgrass.

As it matures, crabgrass plants disperse thousands of seeds to ensure another bumper crop the following season.

A Persistent Weed

Crabgrass is a summer annual; seeds germinate when soil temperatures warm. Plants die in fall after a killing frost. Because seeds can persist in soil for several years, it is important to mow before crabgrass forms seed heads, said Ron Calhoun, a turf expert at Michigan State University.

The first line of defense, he said, is providing an environment inhospitable to seed germination. Cutting your lawn at a higher setting shades crabgrass seeds, reducing germination. As a bonus, the longer turf also shades plant crowns, helping the lawn endure prolonged periods of heat and drought.

Lawns infested with crabgrass the previous season should be treated in spring with pre-emergence herbicides. ‚”The primary disadvantage is that these products are ‚”blanket-applied” and as a result, areas not infested with crabgrass are treated as well,” notes Dr. Fred Yelverton, associate professor and Extension specialist at North Carolina State University.

Mid-Summer Control

By Memorial Day weekend, the opportunity to effectively use a pre-emergence herbicide has passed, leaving homeowners with two options for control: hand-pulling or a post-emergence herbicide.

‚”If you’re going to try and control the crabgrass with post-emergence herbicides, it’s best to get going before the plants really mature,” Frank said.

Products identified as ‚”crabgrass killer” that contain the ingredient MSMA are best used when temperatures are below 80- degrees to avoid burning the lawn, Frank said.

‚”There should be an opportunity to use these products without too much concern for burning the turf,” he said, noting weather patterns that will bring cooler temperatures to areas of the country.

Products containing quinclorac are another treatment option and are effective when applied to crabgrass that is small and actively growing.

Hands-Off Approach

There is another option: do nothing, Frank said.

‚”Remember that sometimes green is better than brown even if it is a weed, especially when considering that it is challenging to establish new turf from seed during the summer to fill in the voids,” Frank said.

Once crabgrass is killed by frost in autumn, infested areas can be over-seeded.

‚”The key to keeping weeds from taking over is to grow a thick, healthy lawn,” he said.