James A. McAfee, Ph.D.
Associate Professor and Extension Turfgrass Specialist
Dallas, Texas
Field sandburs (grassburs) are generally not a problem in well maintainedturfgrass areas. With proper fertilization, mowing and irrigation, you canproduce a turf that is dense enough to prevent sandbur (grassbur)s frombecoming a problem. However, if field sandburs (grassburs) do become aproblem there are several effective herbicides that can be used to controlthis particular weed. The most effective and efficient method of controlis to use a pre-emergent herbicide. Table 1 contains a list of the preemergent herbicides that have sandburs (grassburs) listed as a weed thatis controlled by the chemical in the herbicide. To be effective, these preemergents need to be applied before weed seeds germinate -- generallywhen the soil temperature (NOT the air temperature) reaches 52 degrees F. This usually occurs by March 15 in the central Texas area. In north Texasareas, apply the pre-emergent by April 1 and in southern areas of thestate by March 1. Note: in south Texas and even in central Texas duringmild winters the field sandbur plants will survive and act like a perennialweed. In these cases, a pre-emergent herbicide will not be effective incontrolling these particular plants, but will work on any of the seeds thattry to germinate. If a post-emergence herbicide such as MSMA or DSMA isused, wait until the day time temperatures are about 75 degrees F. for theproducts to be most effective. To insure complete control of germinatinggrass burrs in heavily infested areas, extend the residual of the herbicidebarrier in the soil and thus extend the length of control period by makingapplications of the pre-emergent herbicide EVERY 6 WEEKS throughSeptember. In areas with a light infestation of grass burrs, twoapplications that are 6 weeks apart and after the initial applicationshould control seed germination. As always, the pre-emergent applicationneeds to be watered in thoroughly. Not applying enough water afterapplication of a pre-emergent herbicide is one of the main reason forfailure to effectively obtain control of the annual grassy weeds such assandburs (grassburs).
For post-emergent field sandbur (grassbur) control, use MSMA or DSMA. These products will do a good job of controlling the field sandbur(grassbur) when it is young. As the sandbur (grassbur) matures, itbecomes more difficult to obtain effective control with MSMA or DSMA. Afew years ago, I discovered that by mixing some Imazaquin ( Image ) withthe MSMA you could enhance the control of field sandbur (grassbur). Therate for this mixture is 2.0 lbs. active ingredient per acre of MSMA plus.38 lbs. active ingredient per acre of Image. For example, if using Greenlight's MSMA Crabgrass Killer use 2 Tbsp. per gallon of water and addCyanamide's Image at 6 Tbsp. per gallon of water. The gallon of sprayshould cover 1,000 square feet. Remember, MSMA cannot be used on St.Augustine or Centipede lawns. For these turfgrass areas, you will have torely on the use of a pre-emergent herbicide.
REMEMBER: A dense stand of healthy grass provides the best weedcontrol. Because most weeds are "opportunists" that invade weakenedlawns, the fight against weeds starts with good management. All culturalpractices such as mowing, fertilizing and watering should be done in amanner and time that will favor the grass rather than the weeds. Heightof mowing influences competition against weeds such as crabgrass - thehigher the cut, the lower the infestation. Frequent light sprinklingencourages shallow-rooted weeds and seed germination. Less frequent"deep-soak" watering that maintains a dry surface layer provides thegrass with a competitive advantage.
Temperature, light, soil moisture and other factors determine the timeand extent of weed germination and development. Some weeds germinatein early spring while others sprout in summer or fall. If conditions arefavorable, a weed may be particularly abundant in a given year, but underdifferent conditions the next year, it may be little in evidence.
Herbicide application
Although most herbicides are formulated with reliable safety factors,application rates higher than those recommended may cause injury to turfand other ornamental plants. Many people over apply herbicides, especiallywhen using fertilizer-herbicide combinations. The user needs to followinstructions on containers carefully to avoid overdoses.
before weeds sprout from seeds. Apply two to four weeks ahead ofgermination. Less effective control may be expected if applied more thana month before germination. Applications should not be made until excesslawn clippings and leaf litter are removed. Irrigating immediately afterapplication will help move materials down to the soil.
after weeds appear. Liquid sprays are more effective than dry materials,especially on hard-to-kill weeds. Apply post-emergence materials whenweeds are growing vigorously. Tough old weeds are hard to kill, and ifmature seeds are already formed, the lawn is likely to be infested againnext year. Amine forms are safest because they give off fewer vaporsthat might damage other plants. Volatile ester formulations should not beused around ornamental plants. Select a time when winds are calm toprevent spray drift. Using wax bars or granules impregnated withherbicides near ornamentals will minimize such hazards.
Fertilizer-herbicide combinations are extremely popular becausethey combine two operations. Combinations with pre-emergencechemicals are generally effective since both the fertilizer and herbicideaction are dependent on contact with the soil. Post-emergence herbicideaction depends more on absorption by leaves, and granules in suchcombinations do not adhere well to smooth-surfaced leaves. They willstick better if applied when weed leaves are damp. "Weed and feed"materials present a conflict in desirable actions. Proper time for weedcontrol often does not coincide with the most desirable time and rates forfertilizing. If used for follow-up fertilizations, there is danger ofherbicide overdose.
Equipment
Fertilizer spreaders can be used for applying granular herbicides. Be sure to adjust thespreader to apply recommended rates. If possible, apply half the desired rate in onedirection and the remaining half at right angles to the first application.
A sprayer used for application of 2,4-D and related chemicals should not be used to spraygarden or flower plants. Cleaning procedures are not always reliable. To be safe, have aseparate sprayer for weed-killing purposes.
Eliminating weeds is of little value unless enough desirable grass is present to fill in barespots. A reseeding program deserves first consideration if the turf is so weak that it will notrecover once weeds are eliminated. Study soil and other conditions to determine reasonsfor low vigor of the original turf.
Table 1. Pre-emergent Herbicides Labeled for Sandbur (grassbur) Control
| Brand Name | Common Chemical Name | Company Name |
| PreM | Pendimethalin | Lesco |
| Amaze Grass & Weed Preventor | Benefin/Oryzalin | Green Light |
| Surflan, A.S. | Oryzalin | Southern Ag. |
| Weed & Grass Preventor | Oryzalin | Lilly Miller |
| Weed Stoppere | Oryzalin | Lawn & GardenProducts |
CLASSIFICATION
Common Name: Southern Sandspur (Southern Sandbur) Grassbur
Scientific Name: Cenchrus echinatus L.
Family: Gramineae (Poaceae), Grass Family
SEEDLING The blades are flat and like sandpaper on the upper surface (Plate: seedling ).Theligules are up to 1.6 mm long. The lower papery portion of the ligule is only 0.2 mm longand thefringe of hairs is up to 1.4 mm long.
MATURE PLANT Southern Sandspur is an annual with ascending stem tips from thelowernodes which bend and root. The leaf sheaths are completely without hairs or can have longhairs along the margins. The blades lack hairs above and below, or can have long scatteredhairs above. The seed heads are composed of spiny burs and are 3-14 cm long and 1-2 cmwide. The burs, excluding the spines, are 4.1-6.3 mm wide and 5.3-8.0 mm long to the tipof the spikelets. The spines are of two kinds: 1) flattened spines that are spread over thebody of the bur and 2) fine slender bristle-like spines that are situated in a ring at the baseof the bur. The seed heads appear throughout the year in the South and during the summerand fall in the North.
HISTORY The name Cenchrus is from the Greek word for millet, cenchros . The Greekspeciesname echinatus means armed with spines.