What works against those tough Southern weeds?
Q: We have tried several weed killers, which are supposed to handle Southern weeds, with little to no success. The original was a weed-and-feed I thought may have simply been too old. I went and purchased a new bottle made by Bayer called Bayer Advanced Southern Weed Killer for lawns. It is advertised as a killer of broadleaf weeds and goes on to state "kills 200+ weeds." I had no success, almost as if I had not sprayed anywhere. Do you have any recommendation to kill off the type of weeds we have around St. Petersburg? Gary Myers
Dr. Hort: To be successful at controlling unwanted plants (weeds) with herbicides, you need to identify the plants to be controlled, where they are growing (in turf, plant beds or cracks in the driveway) and the stage of growth (seedling, mature, in seed). For selective weed control — broadleaf weed in turf, for example — plants are grouped as either broadleaf (97 percent of weeds, dollar weed, spurge and dayflower) or grass (2 percent of weeds, crowfoot grass, a summer annual and torpedograss, a perennial). Grasses have a dull leaf blade color and round seed stalks when cut or sedge (1 percent of weeds, purple or yellow nutsedge, with shiny leaves and triangular seed stalk when cut), so the weed or weeds need to be identified to fit into one of these broad classes. (Learn the grasses and sedges. Everything else is a broadleaf.)
Another important weed characteristic is whether it is an annual or perennial. Annual weeds can be successfully controlled with pre-emergent herbicides if applied before the weed sprouts, usually October (to catch the winter annual weeds) and February (to catch the summer annual weeds). Once the weeds are visible, a post-emergent herbicide is necessary.
A great weed identification book is Weeds of Southern Turfgrasses, available online at www.ifasbooks.ifas.ufl.edu for $14. This site is fabulous for everything about your landscape and gardening.
Gary: No weed killer to date has had any impact. It is very soft in texture and the leaves are not much more than a half inch. It grows from a central point and has shoots emanating from a single tap root. Each weed will spread about 6 inches and can support itself several inches above ground level.
Dr. Hort: The weed that you have pictured is called pellitory, Parietaria floridana. Is it in your lawn — if so, what kind of grass — or in plant beds?
Gary: The weeds are in the lawn where we had extensive weeds I finally had to remove by hand, and now this pellitory weed is in the bare spots all over the place. I call the grass kikuyu from my Australian youth, which I was told as a boy originally came from South Africa. It definitely has another name here but I'm not sure if it is called centipede or palmetto.
Dr. Hort: You need to identify your grass (Bahia or St. Augustine, they are the most common) because certain herbicides will damage them. You may kill the pellitory, but also kill your grass.
Gary: Our grass grows out long tentacles which themselves sprout roots every few inches. I will head for the store where we purchased the plugs.
Dr. Hort: If you bought plugs, you have St. Augustine grass. So, to control the pellitory in your St. Augustine grass you will need to apply an herbicide labeled to kill broadleaf weeds, such as Ferti-Lome Weedout, Trimec, Atrazine and others. Be sure to apply according to label directions so as not to damage the turf.
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Gary: Greetings. I am pleased to report that I purchased an herbicide called IMAGE, containing atrazine, and it wiped out the pellitory with one spray. Quite remarkable. The weed went gray and was totally gone.
Dr. Hort: It took a bit to unravel the mystery weed in the mystery grass and I'm glad that you stuck with it and slew the dragon, in this case pellitory, a common winter annual in your St. Augustine grass. The next step is to employ proper cultural practices to your turf: irrigation, fertilization, insect and disease management, along with mowing to create a dense mat to keep the weed seed from germinating next year. This fact sheet should help accomplish the feat: edis.ifas.ufl.edu/lh010.