Over the past couple days I have been receiving several calls and samples of a specific weed folks around the county are encountering in their lawns. It is not a coincidence that these inquiries occurred soon after Memorial Day weekend, which is typically spent enjoying the outdoors with family and friends. The culprit of 100% of those calls was… lawn burweed. Lawn burweed definitely can ruin the fun for those who enjoy going barefoot in their lawn. It is a winter annual that germinates throughout thin turf in the fall months as temperatures cool. It remains small and inconspicuous during the cold winter months. However, as temperatures warm in the early spring, it initiates a period of rapid growth and begins to form spine-tipped burs in the leaf axils. The seed is contained within the hooked bur. It will begin to die in the summer as air temperatures reach 90 °F. However, dead or alive lawn burweed poses a painful problem for barefoot enthusiasts.
Lawn burweed is a low-growing, freely branched winter annual. It has opposite, sparsely hairy leaves that are twice divided into narrow segments or lobes. Leaves are approximately ½-to 1½ -inches long and ¼-to ½-inch wide. It has small (¼ inch or less in width), inconspicuous flowers in the spring. It attains an overall diameter of 6 inches and a height of 3 to 4 inches. The most prominent identifying characteristic of lawn burweed is its spine-tipped burs which are often hard to see but easily felt.
The most important factor about controlling lawn burweed or any weed for that matter, is to ensure quality stand of grass in your lawn. A healthy stand of turf helps shade out and outcompete many weeds. This is achieved through proper cultural management practices such as: proper fertilization, mowing, irrigation, cultivation, and pest management. Simply applying herbicides to a thin lawn to control weeds is the equivalent of putting a Band-Aid on a cut that needs stiches!
Pre-Emergent Chemical Control
Even with proper cultural management weed control is often needed. To control lawn burweed and many of the other problematic winter weeds we see in the early spring it is important to plan ahead. Pre-emergent herbicide applications are the best defense against lawn burweed. However it must be done well before the weed germinates. I recommend to apply these products when temperatures drop to 65-70° F at night which typically correlates to around mid-August to mid-September here in our area. Granular products containing atrazine, isoxaben, or pendimethalin are most effective on burweed. However it is important to check the label and see if the product can be used on your species of grass.
Post Emergent Chemical Control
After applying a pre-emergent products a few lawn burweed plants may slip through and germinate thus spot treatments may be needed. This is where post-emergent herbicides come into play. However once again the timing of these applications are is important. The key is to apply post-emergence herbicides as burweed is spotted during the winter months of December, January and February. The weed is smaller and easier to control during this time of year and has not yet developed the spine-tipped burs. Control is not impossible in March, April, and May, but the spines have already formed by this time and will remain after the weed dies. Liquid products containing atrazine do well on lawn burweed, however it can only be used in St. Augustine and centipede. Products containing 2, 4-D, dicamba, and mecoprop are good to use in Bermuda, tall fescue, and zoysia.
Controlling lawn burweed can be difficult for most homeowners. However with proper cultural management practices and well timed herbicide applications you can once again enjoy your summer lawn barefoot.