By: Richard Bogren
BATON ROUGE – Recent cold weather in Louisiana has caused lawns to go mostly dormant.
If you see green plants in the lawn right now, it’s probably the first flush of winter weeds such as annual bluegrass, chickweed and lawn burweed, said LSU AgCenter turf specialist Ron Strahan.
“Now is a good time to apply selective herbicides like atrazine and Trimec to the lawn to kill these young actively growing weeds,” Strahan said.
Atrazine is good for winter weed control in lawns now through April. Atrazine controls weeds like annual bluegrass, white clover, chickweed, bedstraw and lawn burweed, also known as sticker weed.
The herbicide is good but not perfect, Strahan said. Atrazine is not effective on wild onion, false garlic or blue-eyed grass, which actually is an iris.
Concentrate formulations should be mixed with water in pump-up-type sprayers and with hose-end applicators.
Another option for winter broadleaf management in lawns are herbicides that contain 2,4-D, dicamba and mecoprop as active ingredients. “We usually call these weed killers Trimec-type herbicides,” Strahan said. Ortho Weed B Gon, Weed Free Zone and Trimec are common trade names found at garden centers.
These herbicides work pretty well when sprayed on geranium, annual clovers, chickweed and other broadleaves.
They don’t have any activity on annual bluegrass and are only somewhat effective on wild onion, false garlic and blue-eyed grass.
“Weed control with these Trimec- herbicides can be improved with follow-up applications spaced two weeks after the initial spraying,” Strahan said.
An even more effective way to kill winter weeds is to use both atrazine and Trimec-type herbicides on the same lawn within a week of each other, he said.
For example, you could spray Trimec, Weed B Gon or Weed Free Zone over a weekend and then follow up this application with atrazine a few days later.
Trimec-type herbicides are taken up mainly through leaf absorption while atrazine is mainly absorbed by the root system. This two-pronged attack can be very effective on winter weeds.
“Using both Trimec and atrazine on the same lawn will broaden the weed control spectrum and lead to more satisfying results,” Strahan said.
And you can expect a much higher level of control of dollarweed and lawn burweed when Trimec-type herbicides and atrazine are used on the same lawn.