Many homeowners put out pre-emergence herbicides in the fall to prevent most of these weeds from ever coming up, but it doesn’t always get them all. Nothing is 100% in control and pre-emergence herbicides don’t stop most perennial weeds.
The winter weeds remain relatively small from the time they come up in the fall through most of January and early February. But once the weather begins to warm in late February and March, look out. They begin to grow quickly the rest of the spring. This is usually when everyone wants to take action to kill these weeds because the lawn is still mostly brown and just beginning to green up and the weeds stick out like a sore thumb.
The quicker you take control of these winter weeds the better for a number of reasons.
First of all, younger weeds are much easier to control than larger, mature weeds. The older a weed gets the harder it is to kill. Larger weeds are more likely to need multiple applications of herbicides to kill them, thus costing more in time and money.
Mature weeds also mean seed heads develop on the plant, particularly if you don’t keep them cut. They can release thousands of weed seeds over your lawn making weed control even more of a headache down the road.
The vast majority of herbicides that you can use to kill winter weeds caution against using them during spring green-up of your lawn. The risk of injury from post emergence herbicides is greater during the green-up process than when the turfgrass is dormant or actively growing. Using them can also delay green-up in the spots you spray.
The more common winter weeds you will encounter in the lawn are annual bluegrass (poa annua), wild garlic (most people call them onions), common chickweed, henbit, lawn burweed, vetch, Florida betony, dandelions, Carolina geranium, and cudweed.
The weeds and type of lawn you have determine which herbicide you should select. There are really so many different brand names that I can’t list them all here. The three dominant ones for winter weeds are imazaquin (Image), atrazine and products containing 2,4-D + MCPP + dicamba (Weed B Gon, Weedstop, Weed Killer for Southern Lawns, etc.).
When using atrazine, take precautions not to use it over the root zone of desirable ornamental plants. You also wouldn’t want to use it or the other herbicides if your lawn was newly planted in the fall or winter and didn’t have a chance to root down and become established. And don’t use atrazine if you plan to put out any grass seed within 35 to 40 days after applying it because atrazine also has pre-emergence activity.
Many of these herbicides are sold in fertilizer products called Weed-N-Feed. Don’t use them now as it is far too early to be thinking about fertilizing.
The question always comes up about using Roundup for winter weeds on the lawn during the winter. This has been done with success on Bermuda and zoysia when it is a cold winter, but if there are any green stolons, you could cause some injury. I don’t think there are any green stolons this winter since the last two cold spells. But when there is, usually the injury amounts to nothing more than a slight delay in spring green-up. The advantage of using Roundup is that it will work quicker and better and will eliminate the need for a follow up application.
When in doubt, don’t use Roundup. You definitely would not want to use it on St. Augustine and centipede even though they are as dormant as they have been in several years.
Take control of winter weeds now so you won’t have to deal with them this spring.
Reach Sid Mullis, the director of the University of Georgia Extension Service office for Richmond County, at (706) 821-2349 or firstname.lastname@example.org.