Weed Control Management
Preemergence herbicides are applied to the soil prior to weed seed germination. They provide good control of many annual grassy weeds and are the best weapon agains crabgrass. They also control some broadleaf weeds. Most are in a granular formulation, however, you can find them as a liquid.
Most granular preemergence herbicides should be watered in with about ½ inch of irrigation immediately following application. This activates the herbicide which is absorbed by the young roots and shoots of weeds as they begin to grow.
In the spring, preemergence herbicides should be applied when air temperatures reach 65-70° F for four consecutive days. On average, this is March 1 for the coastal and central regions and March 15-30 for the piedmont and mountains. In the fall, to control winter annuals, apply preemergence herbicides when nighttime lows reach 55-60° F for four consecutive days. On average, this is September 15 thru October 1 for the coastal and central regions, and September 1-15 for the piedmont and mountains.
Preemergence herbicides are generally effective for six to 12 weeks, depending on the product. For season-long control, make a second application nine weeks after the first.
Postemergence herbicides target visible weeds. They are used primarily against broadleaf weeds, perennial grasses, and sedges. The chemicals 2,4-D, dicamba, carfentrazone, triclopyr, clorpyralid, MCPP and MCPA are broadleaf herbicides. They have been combined in many products that control broadleaf weeds. Look for these active ingredients in products such as Spectracide Weed Stop Weed Control for Lawns, Trimec Southern, Bayer Advanced Southern Weed Killer for Lawns and many others.
Centipedegrass (Eremochloa ophiuroides) was introduced into the United States from seed found in the baggage of Frank Meyer, a USDA plant explorer who disappeared on his fourth trip to China in 1916. It was initially used for low-maintenance cemeteries and eventually for lawns during and after the Depression and is sometimes referred to as “lazy man’s grass” or “poor man’s grass”. It is well adapted to the climate and soils of the coastal plains and lower Piedmont areas of the southern United States.
Centipedegrass is a low-growing and medium-textured naturally yellow-green colored perennial turf. It’s low fertility requirements result in slow growth and reduced maintenance. Centipedegrass’ natural color is Granny Smith crab apple green. Overfertilizing to obtain an unnatural dark green color reduces its cold tolerance and usually increases long-term maintenance problems. Centipedegrass is currently the most common home lawn turfgrass in the South.
Centipedegrass is adapted to infertile soils. It spreads by stolons, producing a medium-textured turf. Maintenance requirements are low when compared to other turfgrasses. It has fair to good shade tolerance, good drought tolerance, and can be established from seed or sod. Since it only produces surface runners (stolons), centipedegrass is easily controlled around borders of flowerbeds and walks.
Centipedegrass is highly susceptible to damage from nematodes (especially ring nematodes) and ground pearl insects. Nematode damage limits centipedegrass’ use in deep sandy soils. It exhibits iron chlorosis (yellowing) and produces a heavy thatched if overfertilized. It has poor salt to tolerance and forms a loose turf that is not very wear-resistant, so it will not withstand heavy foot traffic
Stolons from centipedegrass have high lignin content and do not decompose readily, thus developing a thatch layer. The rate of thatch accumulation is a direct result of management practices, which provide excessive vegetative growth. When overfertilized, the subsequent growth means new runners are soon several inches above the soil surface and exposed to the wide fluctuations of temperatures normally experienced in late fall and winter. Within several years, large brown dead patches form in early spring. This dieback is collectively referred to as “centipedegrass decline.” Following proper management techniques can prevent this problem:
• Avoid overfertilizing (e.g., 0 to 2 lb N per 1000 sq.ft. year)
• Prevent thatch accumulation or remove thatch when it exceeds ½-inch in thickness
• Irrigate during drought stress, especially in fall and early spring.
• Maintain a mowing height of 1 ½ to 2 inches.
Improved varieties of centipedegrass are available, including Centennial, Oaklawn, TennTurf (formerly, Tennessee Hardy) TopQuality and TifBlair. The improved cultivars have better cold tolerance than common. However, these must be vegetatively propagated and are selected specifically for their improved cold tolerance. Centennial will perform a little better on alkaline soil than common centipedegrass. The centipedegrass seed and sod produced in most Southern areas are a mixture of red- and yellow-stemmed grasses.
Managing Weeds in Warm Season Lawns
Bermudagrass, centipedegrass, zoysiagrass, and St. Augustinegrass are the most popular warm season turfgrasses grown in South Carolina. Warm season refers to the fact that they prefer warm temperatures of spring and summer. In the winter months, they do not actively grow, but become dormant.
Disadvantages of Weeds
The main reason homeowners want to rid their lawn of weeds is that they are aesthetically disruptive. In other words, weeds are ugly and interrupt an otherwise uniform appearing lawn. Weeds are also fierce competitors and will rob the turf of sunlight, nutrients and moisture. Lastly, weeds have a tendency to spread rapidly. A few left uncontrolled can quickly become a problem.
Types of Weeds
Grassy vs. Broadleaf: Grassy weeds emerge from seed as a single leaf. The leaf blades are longer than they are wide and have parallel veins. An example is crabgrass or Dallisgrass.
Broadleaf weeds emerge from seed with two leaves. Leaves have netlike veins and many, like dandelion or clover, have showy flowers.
Annual vs. Perennial: Annuals germinate, grow, and die within a twelve month period. Summer annuals, such as goosegrass, germinate in the spring, grow through the summer, set seed, and die at the onset of cold weather. Winter annuals, such as chickweed, germinate in the fall, grow through the winter, set seed and die as temperatures rise in early summer.
Perennials grow for two or more years. They reproduce from vegetative parts such as tubers, bulbs, rhizomes, or stolons, though some also produce seed. Perennials tend to be the most difficult to control. Examples are dallisgrass, wild garlic and nutsedge.
Weed control begins with proper management practices, which encourage a dense, healthy turf. A healthy turf shades the soil so that less sunlight reaches the ready-to-germinate weed seeds. A thick turf minimizes the space available for weeds to become established. Proper management practices include mowing, watering, fertilizing and liming.
Depending on the type, warm season grasses should be mowed at heights of ½ to 2 inches and frequently enough so that no more than 1/3 of the blade is removed. Proper mowing heights will encourage a dense, healthy stand.
When lawns show signs of drought stress, water deeply so that the entire root zone is wet. During dry periods, this will be every five to seven days. This practice encourages a healthy root system.
Fertilize and lime at the proper time and according to a soil test. Proper lime application will help to maintain a soil pH where nutrients are readily available to the turf.
St. Augustinegrass (Stenotaphrum secundatum) grows best during the warm (80 to 95° F) months of spring, summer and early fall. It grows vigorously during this time and becomes brown and dormant in winter. This grass has large flat stems and broad coarse leaves somewhat similar to centipedegrass. It has an attractive blue-green color and forms a deep, fairly dense turf. It spreads by long, above-ground runners or stolons. While it is aggressive, it it easily controlled around borders. It is commonly planted by vegetative means because of problems with seed viability.
St Augustinegrass is the most shade-tolerant warm-season grass. It is very susceptible to winter injury, especially if planted farther west than Columbia. It is well-suited for the coastal plain. Perhaps the greatest disadvantage of this grass is its sensitivity to an insect, the chinch bug. Chinch bugs can cause extensive damage to St. Augustinegrass if not controlled early.
The more common St. Augustinegrass cultivars are Bitterblue, Floratine, Floratam, Raleigh, Jade and Seville. Bitterblue, Floratine and Floratam are less tolerant of cold and should only be grown in coastal areas of South Carolina. Bitterblue has a finer, denser texture and darker blue-green color than common St. Augustinegrass. It also has the best shade tolerance but is not resistant to chinch bugs or gray leaf spot disease.
Floratine is an improved selection from Bitterblue that has a finer leaf texture and lower, denser growth habit that allows closer mowing than with common St. Augustinegrass. It is not resistant to chinch bugs but tolerates light to moderate shade. Floratine’s other characteristics are similar to Bitterblue’s.
Floratam is an improved type of St. Augustinegrass that has chinch bug and SADV (St. Augustinegrass decline virus) resistance, and reddish stolons (runners). It has very coarse texture and poor cold and shade tolerance. It will thin in direct relation to the amount of shade received. Its winer and early spring color is lower as it goes into a deep semi-dormancy period and sheds its leaves more than other cultivars. Spring green-up is also slow. Floratam is one of the preferred cultivars to plant in open sunny areas where chinch bugs are a problem; however, research has identified a strain of chinch bugs which can damage Floratam.
Raleigh is a cold-hardy cultivar that has a medium green color with a coarse texture. It is susceptible to chinch bugs and brown patch disease. During peak summertime heat, Raleigh has been noted to yellow and not spread as aggressively as during cooler temperatures. Supplemental iron applications are needed to reduce this yellowing tendency. Raleigh is best adapted to heavier, organic, clayey soils with a medium to low soil pH.
Seville is a semi-dwarf cultivar with a dark green color and low growth habit. Seville is susceptible to chinch bugs and webworm damage and is cold-sensitive. Due to its compact growth habit, Seville tends to be thatch-prone and shallow rooting. It is resistant to SADV and has a finer texture than Floratam. Seville performs well in the shade and produces an excellent turf in full sun. Its cold tolerance is similar to Floratine’s. Being a semi-dwarf variety, Seville’s maintenance is different than for the taller growing cultivars.
Jade has a good shade tolerance, a semi-dwarf growth habit and dark green color. It is susceptible to chinch bugs, sod webworms and brown patch disease and is cold sensitive.
Zoysiagrasses (Zoysia species) grow best during the warm (80 to 95 °F) months of spring, summer and early fall. They grow vigorously during this time and become brown and dormant in winter. They are adapted to the entire state and are some of the most cold-tolerant of the warm-season grasses.
These grasses form an excellent turf when properly established and managed. For the best appearance, zoysias require cutting with a reel mower, although a rotary mower with sharp blades is satisfactory. They also require occasional watering and periodic thinning or dethatching. Once this grass is established, thatch can build up, especially when heavily fertilized. Remove thatch every two to three years.
The zoysias form a dense, attractive turf in full sun and partial shade, but often thin out in dense shade. Most zoysias grow very slowly compared
to other grasses and usually are established by sprigging or plugging, although there are seeded types. Sprigs or plugs, 2 inches in diameter planted on 6-inch centers, will cover completely in two growing seasons if watered and fertilized properly. However, it may require several years to cover if not properly maintained. As it is a slow grower, it requires less frequent mowing than some other grasses. It will, however, recover slowly from damage due to its slow growth habit.
Zoysia japonica is sometimes called Japanese or Korean lawngrass or common zoysia. It has coarse leaf texture, excellent cold tolerance, and it can be seeded.
Meyer zoysia, also called “Z-52,” is an improved selection of Z. japonica. It has medium leaf texture, good cold tolerance and spreads more rapidly than
most other zoysias. This is the zoysia often advertised as the “super” grass in newspapers and magazines.
Belaire is also an improved Z. japonica variety noted for its excellent cold tolerance and medium green color. It has a coarser leaf texture and faster
rate of establishment than Meyer. It is susceptible to brown patch disease.
Emerald zoysia is a fine-textured hybrid that is possibly the most attractive zoysia. It is well-suited for top-quality lawns where a good maintenance
program is provided. Emerald zoysia has less winter hardiness but more shade tolerance than Meyer. It has a dark green color, a very fine leaf texture, good shade tolerance, high shoot density and a low growth habit. Emerald will develop excess thatch rather quickly if overfertilized and is prone to winter injury northward from the Columbia area.
El Toro is a relatively new zoysia that was developed in California and looks like Meyer zoysia. It is the fastest growing zoysia, tolerates mowing with a rotary mower and produces less thatch than Meyer. The winter hardiness of this grass is not well-established although it can be found growing in the Columbia area.
Zenith is a hybrid zoysia that is available as seed. It has a medium dark green color, a medium density, and will tolerate light shade. It is planted in late spring to early summer with a seeding rate of 1 to 2 pounds of seed per 1000 square feet. The seed should be very lightly covered with soil by raking.
Cover the seeded area with straw to retain soil moisture during the germination period. Water the newly seeded lawn very lightly three or four times per day to keep the seed moist for best germination.