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Act quickly to control summer lawn weeds
MISSISSIPPI STATE -- When homeowners look out in the spring and see more weeds than grass, it's time to take action to beautify the lawn.
Winning the battle of the weeds begins with a two-part effort. Eliminate existing winter weeds in yards and apply pre-emergence herbicide to prevent summer weed seedlings from establishing.
"If you've not done anything before, you've got to jump in at some point in time if you want a well-groomed, manicured lawn," said John Byrd, weed specialist with the Mississippi State University Extension Service.
Start by mowing the turf as close to the ground as possible and removing the clippings.
"This takes the competition off the lawn, and lets the soil warm up faster and the grass begin to grow," Byrd said.
The next step is to apply herbicides.
"It is critical to put down a pre-emergence herbicide that will take care of the annual grasses and weeds that will come as the soil warms up and we move into summer," Byrd said.
Wayne Wells, Extension turf specialist, said post-emergence herbicide will kill existing winter weeds and pre-emergence herbicide will prevent summer weeds from getting established.
"Crabgrass is the No. 1 summer annual we try to take care of in the spring with pre-emergence herbicides," Wells said. "Crabgrass germinates when the soil temperature reaches 55 to 58 degrees for three or more consecutive days."
Gardeners on the Coast already missed their opportunity this year to see good results from pre-emergence herbicide, but those in most of the rest of the state should do it by early March.
The dinitroaniline or DNA class of pre-emergence herbicides inhibit cell division, and are effective on most small, seeded summer annuals like crabgrass, goosegrass and spurge.
"When one of these small seeds germinates and its root tip comes in contact with the herbicide, the cells can't divide and it can't develop a root system to support it," Wells said. "When it uses up the stored food in the seed, it just dies."
Several turf herbicides with this mode of action include benefin, prodiamine, pendimethalin, oryzalin and dithiopyr. These are safe for all of Mississippi's warm-season grasses, but always consult the label for application information.
Post-emergence, hormonal-type herbicides that regulate growth are often used for controlling weeds such as clover, wild garlic, henbit, chickweed and many other broadleaf species from winter growth. Dicamba, 2, 4-D, clopyralid, triclopyr and mecoprop, also known as MCPP, are good examples of this type of chemistry. These chemicals commonly are used in combination or three-way mixes to broaden the spectrum of control.
Herbicides typically are available in granular or liquid form.
"I prefer applying chemicals in a water carrier as a carefully calibrated spray. With herbicides, it is the active ingredient rate on an area basis that is most critical," Wells said.
While a particular herbicide may be labeled for use on all the warm-season grasses found in the state, each species may tolerate the chemicals at different concentrations. Always follow label instructions when applying lawn chemicals.
"Be sure the herbicide you put out controls the weeds you actually have and that your turf species is tolerant of the chemical," Wells said.
The weed scientist said a lot of people are fighting with lawn burweed, a weed with a lot of stickers, in lawns in the spring. Byrd said three-way herbicide mixes or atrazine will control this pesky weed.
Many herbicides come mixed with a fertilizer as a weed and feed blend. Both specialists cautioned homeowners from putting out fertilizer too soon.
"If you choose to use a weed and feed, choose one with a very low nitrogen content," Byrd said. "Nitrogen greens up the lawn by causing the leaf blade to grow, but turf this early in the season needs to be putting down roots instead."
Extension publications 1322 and 1532, Establish and Manage Your Home Lawn and Weed Control Guidelines for Mississippi, are available from county Extension offices or online at http://www.msucares.com/pubs.