Released: August 27, 2003

The Lawn Weeds Are Ahead, But Wait Before Fighting Back

MANHATTAN, Kan. – Drought stress – particularly in cool-season tall fescue and Kentucky bluegrass – is creating a heyday for Kansas lawn weeds.

“Our county agents and state specialists both are having to field numbers of phone calls every day,” said Ward Upham, who coordinates the Horticulture Rapid Response Center for Kansas State University Research and Extension.

He and the other horticulturists can’t offer much hope for an immediate solution.

“You can try a few management changes now that may make a difference,” Upham explained. “Mostly, however, you have to plan for what you’ll do in months ahead – for when you’re not being reminded about the problem as often, but the time for making a real difference will finally arrive.”

The dog days of summer are the best time to apply herbicides only if you plan to kill the entire lawn and start over, Upham explained.

“And, to get rid of some of the tougher weeds, you generally have to make two applications, several weeks apart. So Kansans who plan to do this kind of replanting are already running close to the usual deadline for getting a lawn renovation done before winter sets in,” he said.

In established lawns, the annual weeds – including crabgrass and spurge – are at peak strength now and trying to go to seed. Spot applications of broad-spectrum herbicides won’t be very effective at killing the plants. They won’t have any effect on the viability of the seeds deposited for next year’s weed crop.

“About the best you can do now is to hand pull annual weeds as soon as possible. Or, you can try to keep their flowers mowed off, so they can’t go to seed,” the horticulturist said.

Most perennial broadleaf weeds, such as dandelions and clover, aren’t too robust now. They’ll respond to spot treatments, but homeowners’ control rate won’t be as good as it will when the weather cools somewhat.

“When cool-season turfs make their fall comeback, the broadleaf weeds do, too. Both produce lots of new greenery and start storing energy in their roots for winter,” Upham said. “With weeds, that gives you more leaf surface area to treat and greater odds that you’ll kill the roots, as well as the upper plant.”

Timing can be difficult, however, if homeowners also plan to overseed drought-thinned cool-season lawns by Oct. 15.

“Broadleaf weed herbicides can be hazardous to seedling turf’s health,” the horticulturist said. “You need to wait until the new grass grows enough to merit mowing three times before you worry about weed control. If you overplant early enough, though, you could be treating broadleaf weeds by November.”

The top recommendation for weed control in Kansas has always been to grow thick, healthy turf, he said. And the No. 1 recommendation for accomplishing that is to feed tall fescue and Kentucky bluegrass in September – whether replanting, overseeding or just encouraging the lawn.

“The second most beneficial time to feed those lawns is in November,” Upham said. “And if you want to get a jump start on controlling annual crabgrass, too, you can look for one of the products that combines a high-nitrogen fertilizer formulation with the long-lived crabgrass preventer prodiamine.

“By applying it, as well as your broadleaf weed control, you’ll be well ahead of the weeds next spring. Plus, your lawn’s second feeding will make the grass thicker and better able to withstand winter’s stresses. Your turf will be likely to green up earlier next year, and it’ll be better prepared to crowd out any weeds that remain,” Upham said.

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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.

Story by:
Kathleen Ward, Communications Specialist
kward@oznet.ksu.edu
K-State Research& Extension News