Timing Crabgrass May Be Unusual Challenge 3/21/02

Good timing isn’t the only thing that helps crabgrass preventers do their job. A thorough and even application is vital, too.

Kansas State University horticulturists advise following these steps:

1. Check the applicator manual or talk to someone who knows the equipment well. Make sure the applicator is calibrated to release the correct amount of herbicide when operated at your walking pace.

2. Take at least a rough measure of your lawn’s square surface area, to help determine the amount of herbicide to use.

2. Make two passes over the lawn, the second at right angles to the first.

3. If permitted by the herbicide label, lightly water the crabgrass preventer in, to help it spread out more evenly and to move it down into the soil.

MANHATTAN, Kan. -- Timing can make all the difference in whether crabgrass controls work or waste time and money.

Many Kansans already miss the control "window" every year. Unfortunately, 2002’s unusual and sometimes swiftly shifting weather could worsen their odds for success, said Kansas State University horticulturist Matt Fagerness.

"Homeowners need to remember that you can apply crabgrass preventer as soon as an established fescue or bluegrass lawn greens up and starts growing well. A couple of weeks after that are okay for an application, too. But if they wait any longer, they’re too late," he said.

Crabgrass preventer is a pre-emergence herbicide. If applied after annual weeds emerge for the year, pre-emergence herbicides simply can’t do their job, explained Fagerness, the turfgrass specialist for K-State Research and Extension programs.

Kansans used to have a fairly reliable gauge for when to apply each year’s crabgrass controls, he said. They waited until the redbud trees bloomed.

"But many people still using redbuds as their guide are being misled," Fagerness said. "The only accurate indicators are native redbuds, which Kansans often used to have growing in their yards. Today’s landscape hybrids have a range of bloom dates, so aren’t as reliable for targeting crabgrass. The native redbuds you see along the highway may not accurately represent what’s happening in your yard, either."

During more typical years, the horticulturist recommends that the majority of Kansans consider April Fools Day as the absolute latest for their first crabgrass preventer application. [See related story for more about second applications.] His only exceptions:

* New lawns and newly overseeded sections that haven’t grown enough to need mowing three to four times since planting. Pre-emergence herbicides sometimes harm young, shallow turfgrass roots.

* Cool-season lawn turfs treated with a fertilizer-Barricade combination last fall. They’ll still have crabgrass protection, and another preventer application in spring could "burn" the lawn.

K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.