Spring is approaching and the main thing on my mind is controlling annual weeds. The most effective way to control crabgrass and other summer annual weeds is with a pre-emergent herbicide. Pre-emergent herbicides should be applied prior to weed seed germination. They don’t prevent germination, but they do prevent emergence of shoots and roots by forming a barrier on the soil surface.
Crabgrass growing in centipedegrass lawn. Photo credit: UF/IFAS Extension
Summer annuals such as crabgrass and chamberbitter begin to germinate when soil temperatures warm in the spring. Preemergence herbicides should be applied when daytime temperatures reach 65oF to 70oF for 4 or 5 consecutive days to form a barrier to help prevent these weeds from emerging. This is about the same time azaleas and dogwoods begin to bloom. Goosegrass is the exception for this temperature rule. For good goosegrass control, preemergence herbicides should be applied 3 to 4 weeks after the suggested daytime temperature application date.
It is important to note that you should only use preemergence herbicides on lawns that have been established for at least a year. These herbicides are prone to injure newly planted lawns. In addition, many preemergence herbicides may interfere with lawn grass seed germination, so make sure to refrain from reseeding for at least six after application.
Commonly available preemergence herbicides contain the active ingredients oryzalin, benefin, pendimethalin, DCPA and bensulide. However, there are a wide variety of products on the market. For more information on weed management please read the UF/IFAS publication “Weed Management Guide for Florida Lawns”.
Worm mounds in bermudagrass. Photo credit Mary Salinas, UF IFAS Extension.
The April 8 program of Gardening in the Panhandle LIVE! was focused on turfgrass, quite a popular topic in the springtime as the weather warms and turf comes out of winter dormancy. Here are some of the questions asked of our University of Florida experts and the links to resources they shared.
Q. How well do new turfgrass varieties thrive against weeds?
A. A healthy and properly maintained lawn is your best defense against weeds and other pests. Additionally, ProVista is a new cultivar of St Augustinegrass that can tolerate glyphosate so it makes it much easier to kill weeds in the lawn. ProVista is not yet widely available in the panhandle.
Q. What to do about bare spots in St Augustine turf in shade?
A. Rough up the ground and put ½ to 1” compost and let the grass fill in or plant plugs. St. Augustinegrass for Florida Lawns: https://edis.ifas.ufl.edu/lh010
Q. When is the best time to overseed? I have a centipede lawn that’s 15-16 years old and I’m trying to bring it back to health.
A. Be sure to be following good practices and centipedegrass should not fail. Overseeding may not be the best option. Centipedegrass for Florida Lawns: https://edis.ifas.ufl.edu/lh009
Q. How do I repair lawn areas ruined by piled up Hurricane Sally debris?
Gallery, with the active ingredient isoxoben, has always been the best product to control chamberbitter. Another product, Gemini, adds prodiamine with isoxoben and also provides good control.
Q. How do you get dollar weed under control?
A. Control irrigation. Dollarweed loves lots of water so make sure you are not overwatering. See: https://edis.ifas.ufl.edu/ep389
Q. I used Image to help control Bahia in Centipede. Anything else that we can use?
A. Metsulfuron methyl, 3 applications every 21 days
Q. Which postemergence herbicide is safe and effective for reducing oxalis in a lawn?
A. First you need to determine which fungus, if any, is responsible. Key to Identification of Landscape Turfgrass Disease: https://edis.ifas.ufl.edu/lh064
Weeds identification and management is still one of the most common questions we receive at the local UF IFAS Extension office. Learn about the chamberbitter weed that can grow in turf and ornamental beds and the multi faceted approach that is necessary for management In the Garden with Beth Bolles, UF IFAS Extension Escambia County.
Figure 1: Chamberbitter, a common annual weed. Credit: Mary Salinas, UF/IFAS Extension Santa Rosa County.
With daily rainfall occurring regularly, coupled with humid temperatures, summer annual weeds have had a mighty boost in growth. Chamberbitter, Florida pusley, sedge and oxalis are just some examples of the many weeds that are exploding across our landscape.
Chamberbitter (Phyllanthus urinaria) is found as north as Illinois and as west as Texas, but thrives in lower southeastern states. It’s a headache for homeowners as well as pasture managers. The foliage resembles that of the mimosa tree (Albizia julibrissin) and can be confused with the native mimosa groundcover, known as powderpuff mimosa (Mimosa strigillosa). This plant grows upright and develops a long taproot. Wart-like seeds can be found on the underside of the branch.
Florida Pusley (Richardia scabra L.) also known as Florida snow or Mexican clover, has recently blanketed landscapes in the Panhandle with white flowers. It’s a persistent weed that moves quickly.
Sedges and sedge-like plants (Cyperus ssp.), known as kyllinga, are species that emerge in late spring and thrive in summer months in warm, moist climates. Excessive irrigation or areas with poor drainage create a very hospitable environment for these weeds. Sedges are annual grass-like plants have an elaborate flower-bearing stems. Yellow and purple nutsedge are the most common species. Kyllingas have smaller leaves and are less vertical. Sedges and kyllingas are fast spreading, and reproduce through seed and rhizomes, or underground tubers.
Oxalis or yellow woodsorrel (Oxalis stricta) have heart-shaped lobes and have a bright yellow flower. Oxalis reproduces by seed and have a narrow “okra-like” seed pod.
Credit: Stephen H. Brown, UF/IFAS Extension Lee County
What about control? Some cultural control methods are hand removal and mowing frequently to offset the life cycle, but these practices alone will most likely not solve the problem. There are many broad spectrum herbicides that can be used to control these weeds with good results, but you must be persistent. Some are season long applied products. However, most effective products need to be applied in cooler temps than we have now. Consecutive days of temperatures of less than 90 degrees would be optimal. Applying the chemical otherwise will most likely harm the turfgrass. Be aware, some productions will injure or kill centipede and St. Augustine, but are safe to use on other turfgrasses like bermuda, bahia and zoysia. Be sure to read the label and follow the directions and precautions.
Another option is non-selective herbicides, like glyphosate, which can be used in thick patches or for spot treatment. When using a selective herbicide, remember to protect turfgrass and other plants from spray drift or any contact, especially regarding ornamental plants and trees.
Contact your local county extension office for more information.
Supporting information for this article is from the following online publications:
UF/IFAS EDIS publications: “Yellow Woodsorrel (Oxalis) Biology and Management in Turf” by J. Bryan Unruh, Ramon G. Leon, and Darcy E. P. Telenko: http://edis.ifas.ufl.edu/pdffiles/EP/EP38500.pdf
