Managing Weeds in Florida Lawns
A weed is a plant in the wrong place or one that you do not want in your turfgrass. The first step in considering any type of weed control is to appropriately identify the weed. Control without weed identification may well create more issues, including turfgrass damage or death.
There are several types of turfgrass weeds based on growth habit and life cycle. Growth habit weeds include the following:
- Broadleaves—Two seed leaves at germination, true leaves with net-like veins, and generally showy flowers; clover, beggarweed, matchweed, etc.
- Grasses—One seed leaf, hollow rounded stems with joints and parallel veins in their true leaves; crabgrass, annual bluegrass, torpedograss, etc.
- Sedges/Rushes—Sedges have triangular-shaped solid stems. Rush stems are round and solid. Both prefer moist habitats; yellow and purple nutsedge, etc.
Life cycle weeds include the following:
- Annuals—life cycle is completed in one growing season.
- Biennials—life cycle is completed in two growing seasons; vegetative growth in the first growing season and flowering in the second.
- Perennials—life cycle is completed in three or more years.
The most successful weed control is based on proper turfgrass management practices that are used to create a dense and healthy yard. Consider the first of nine Florida-Friendly Landscaping TM principles: right plant, right place. Match the turfgrass variety with the site conditions of sun and shade. All turfgrasses, even those that are shade tolerant, require a minimum of five to six hours of sun each day. Bermudagrass and bahiagrass do not thrive in any shade conditions, which makes them more susceptible to weeds.
Proper cultural practices are required for dense turf to be capable of preventing weed infestations. Cultural practices include fertilization, watering, mowing, and pest control. Over and underperforming any of these practices increase the likelihood of weed invasion.
Both foot and vehicle traffic can damage turfgrass, which, again, is an invitation for weeds. Soil compaction and excessive water saturation should be corrected. Pests that disrupt/create holes in the soil surface, such as mole crickets and armadillos, create open areas, which encourage weed populations.
Lynn Barber, Agent
University of Florida/IFAS Extension, Hillsborough County
Lynn Barber, Agent, University of Florida/IFAS Extension, Hillsborough County, is responsible for educating residents on the nine principles of the Florida Friendly LandscapingTM program. These principles include right plant right place, water efficiently, fertilize appropriately, mulch, attract wildlife, manage yard pests responsibly, recycle, reduce stormwater runoff, and protect the waterfront. Barber is past president of the Florida Association of Natural Resource Extension Professionals and has received numerous awards for programming, publications, and television and radio segments. As a Master Gardener, she has given back thousands of hours in environmental horticulture education to the community.
Prevention is easier than control. Consider a groundcover instead of turfgrass in heavily-shaded areas. Scout your turfgrass regularly to identify potential weed and pest issues. Avoid parking, driving, and excessive walking on your yard. Water appropriately, ½–¾ inch per event, which includes rainfall. Fertilize appropriately, two to three times per year, and if you leave your grass clippings on your turfgrass, you can decrease fertilizations to one to two times per year.
Edis weed seed shapes
By Jane Morse, University of Florida/IFAS Extension Agent, Pinellas County Extension
Weeds in Florida can be a nightmare. Abundant summer rains and scorching sunshine lead to lots of germinating (sprouting) weed seeds. Weed control in the fall isn’t too bad, but trying to keep up with weeds in the blistering heat of summer, while dodging rain storms, sweating, and swatting mosquitoes is miserable.
To control weeds we need to have a basic understanding of some of their differences and how we can use these differences to our advantage.
First, let’s learn about the types of weeds. There are broadleaf weeds. These types of plants generally have net-like veins in their leaves and many have showy flowers. Some examples are dollarweed, creeping beggarweed and Florida pusley. Grass weeds have hollow, rounded stems and nodes (joints) that are closed and hard. The leaf blades have parallel veins and they are much longer than they are wide. The leaf blades also alternate on each side of the stem. Some examples are crabgrass, torpedograss and sandbur. Sedges are “grass-like” weeds, but they are not true grasses. Sedges have a solid, triangular-shaped stem with leaves that extend in three directions. Examples include yellow nutsedge and purple nutsedge.
Plants are also distinguished by how long they live. Some are annual (they germinate, grow, flower, seed and die in one year). Others are biennial (it takes two years to complete their life cycle). The hardest to control plants are perennial (they live more than 2 years) because they have several means of reproducing. Not only may they reproduce by seed, but they may reproduce vegetatively by bulbs, rhizomes, stolons, or tubers.
There are two basic methods of weed control — physical control and chemical control. Usually the best control is achieved using a combination of these two methods.
Physical weed control includes mowing, hand pulling, hoeing and mulching. Many weeds in turf can be controlled by proper mowing. In general, Bahia and St. Augustine grass should be mowed at a height of 4 inches and mowed frequently enough so that only 1/3 of the leaf blade is removed each time. Hand pulling can be used if there are a small number of weeds. Mulching is a good weed control method for flowerbeds, footpaths and other areas where there is no grass. Mulch works by smothering out weeds by excluding light. Mulch should be applied about 2 inches thick and kept away from the bases of plants.
Chemical weed control is the use of herbicides. There are different types of herbicides. Selective herbicides control certain plant types without seriously harming other plant types. A selective herbicide might kill broadleaf plants while not seriously harming grass plants, or vice versa. Non-selective herbicides kill most plants regardless of type. Roundup® (Glyphosate) is probably the most widely known and used non-selective herbicide. Then there are pre-emergent herbicides that prevent seedlings from growing and post-emergent herbicides that are applied to existing weeds when they are small and actively growing.
Selective herbicides can be very useful if, for example, you are trying to control grass weeds in a broadleaf planting, or trying to control broadleaf weeds in a grass planting. Grass-B-Gon® (Fluazifop) is a selective herbicide that kills unwanted grasses in and around broadleaf ornamentals. Manage® (Halosulfuron-methyl) is a selective herbicide for controlling nutsedge in turfgrass and landscaped areas.
Non-selective herbicides are most commonly used for killing plants in a large area. For example, if you were replacing a turfgrass area and wanted to clear the area of all plants a non-selective herbicide would be a good choice.
Pre-emergent herbicides offer very good weed control because they keep the weeds from sprouting and growing. Some weeds like crabgrass can only be effectively controlled with a pre-emergent herbicide. Pre-M® (pendimethalin) is a pre-emergent that controls some annual grasses (crabgrass, etc.) and certain broadleaf weeds. It can be used on St. Augustine or Bahia grass and on many ornamentals for weed control. The most important thing about pre-emergent herbicides is timing. They must be applied before the weed seed germinates. Therefore it is important to know the identification of the weed you want to kill and when it germinates.
Post-emergent herbicides are applied to already existing weeds. They work best on young, rapidly growing plants. Some herbicides control some weeds better than others. Again, it is important to correctly identify the plant you want to kill so the best herbicide can be selected to obtain effective control.
Whenever chemicals are used it is extremely important and crucial to read the label and follow the directions exactly. Not following the label directions can be harmful to the environment and people, and is against the law.
For more information or help selecting herbicides contact your local University of Florida Extension Service in Pinellas County at 727-582-2100. Visit our website at: http://pinellascountyextension.org or come to our office at 12520 Ulmerton Road, Largo, FL. Office hours are M-F from 8AM to 5 PM.
Note: Use of brand or trade names in this publication does not imply endorsement of the products or criticism of similar ones not mentioned. Trade names are used herein for convenience only. Mention of a proprietary product does not constitute a guarantee or warranty of the product by the author.
Gardening: Sedges can be the worst of the weeds
Many homeowners bringing in plant samples for identification are often surprised to find out that one very green vigorous plant is in fact a weed. This weedy plant is a sedge and it becomes so prolific, it may take over sections of the lawn or plant bed.
Sedges can be annuals (survives for one growing season) or perennials (lives multiple years). Unlike grasses, sedges have triangular stems. Rolling the flower stem between your thumb and forefinger indicates that the stem is not round but has three distinct sides. Like grasses, sedges produce a seed head at the top of this stem. Some types of sedge only reproduce by seed, while others have a creeping underground stem called a rhizome. The hardest ones to control also have underground tubers called nutlets, which are attached to the rhizome and the sedge type can sometimes be identified by taste if one is adventurous.
These plants are adaptive and will invade lawns, vegetable gardens and/or plant beds. For vegetable gardeners using plastic or landscapers using weed cloth to choke out weeds, sedges are persistent and will poke through these barriers. They are easier to control in plant and vegetable beds by hand as long as the individual weeding is persistent and remove the underground rhizome and/or nutlets. If only the top is removed, the weeder will be back working the same area again and again. Control in lawns is a different story altogether. Because the rhizomes and nutlets are intermingled with the lawn roots, pulling is not an effective option. To tackle these weeds, one must first correctly identify the sedge.
The most common types in both landscape beds and lawns include yellow nutsedge, purple nutsedge, green kyllinga and globe sedge. All of these are perennials, so they will be a permanent fixture year after year.
Purple nutsedge is an aggressive plant and is considered by many to be the world’s worst weed. This sedge has underground runners that link plants together and nutlets that are bitter in taste. Please don’t attempt the taste test if pesticides have been used. Plants can reach a height of 1?1/2 feet tall and develop a seed head with red to purple brown spikelets. The leaves are in groups of three and are dark green and glossy. Leaves have a distinct mid-vein, are 1/8 to 1/3 inch wide, and end abruptly in a sharp tip that is boat-shaped. This weed loves sunny areas where soils are moist and sandy.
Yellow nutsedge is often confused with purple nutsedge. Leaves of yellow nutsedge can reach two feet in height and are often taller than the seed head. Leaves are also in groups of three and are yellow-green in color. Leaf width is 0.2 to 0.5 inch in width and gradually taper to a thin tip. Seed heads are yellow in color and the tubers are somewhat sweet in taste (not bitter). These do have an underground rhizome, but end at the tuber so are not connected by a chain as is purple nutsedge. Yellow nutsedge will grow in sunny areas in wet or dry soils.
Globe sedge has a little different growth habit in that it forms a dense clump. Plants can reach 20 inches in height and grows in dry to moist sandy soils. The seed heads have three to seven leaflike bracts at the top of the stem with a cluster of globe shaped seed heads that are green which age to brown or black. Globe sedge doesn’t have nutlets but reproduces by seed or short rhizomes.
Green kyllinga also has a different growth habit in that it forms a dark green mat, plants are usually only 6 inches tall, and leaves are very narrow. Plant rhizomes are purple and the seed head has three leaflike bracts with one round seed head at the center (occasionally may be two or three seed heads). Kyllinga reproduces by both seed and rhizomes and thrives in low, moist areas.
Once the sedge is correctly identified, control options can be considered. One obvious cultural option for sedges that prefer moisture is to change the habitat so the area is dry. Is there a broken sprinkler head in the area, are you over-watering, or is there a drainage issue from roof runoff? Some sedges prefer sun and will not tolerate shade, so covering the area with cardboard or multiple layers of newspaper will help in control without the use of herbicides.
A dense turf or ground cover will help shade out weed seeds that require light for germination. Likewise, mulch will also prevent germination of weed seeds in landscape beds. Trials indicate the most effective mulch is one that has large particles because it provides more shade and dries out quicker.
In plant beds and vegetable gardens, hand weeding is the best option, but one must be diligent to remove all underground plant parts. If hand weeding is not possible, another option is to remove the above ground portion and then spot spray with a systemic herbicide like glyphosate as the young plant emerges from the underground rhizome or nutlet.
In lawns, there are three chemicals readily available to homeowners based on the type of sedge and lawn. To control yellow nutsedge and kyllinga, apply bentazon (Basagran T/O) which is safe on all five of our warm season lawn types; bahia, zoysia, Bermuda, St. Augustine, and centipede. Bentazon is a contact herbicide and will not control the rhizomes or nutlets, so repeat applications will be required. For purple nutsedge, yellow nutsedge, green kyllinga and many of the other types of sedges, apply halosulfuron (Sedgehammer) or imazaquin (Image). Halosulfuron is safe on all five lawn types and imazaquin is safe on all except bahiagrass. Again, repeat applications may be necessary for eventual control. Keep in mind that imazaquin is also a growth regulator and will likely slow down growth of the lawn. It may reduce the need to mow as frequently, but on the negative side, the grass may not recover as quickly from injury. If an area is completely infested with sedge weeds, it may be more effective to treat with a broad spectrum systemic herbicide like glyphosate. Read the label carefully.
If the intent is to plant ornamentals, there are restrictions about how soon they can be planted following application of these products; a year for imazaquin and three months for halosulfuron.
Back in the day, pigs were used to help control weeds. Farmers fenced in areas that were under attack by weeds and in came the pigs which were very effective at foraging the weeds including the underground nutlets. The other benefit was the added fertilizer from the manure.
The bottom line is that sedge weeds are very difficult to control. If you are happy with the appearance and can accept this grass-like weed, it may be easier to adopt the saying “If it’s green, mow it!”
For more information on the identification and control of sedges, go to edis.ifas.ufl.edu/hs205, edis.ifas.ufl.edu/ep141, edis.ifas.ufl.edu/ep523 and edis.ifas.ufl.edu/ep492.
Terry Brite DelValle is a horticulture extension agent with the Duval County Extension Service and the University of Florida/IFAS.