Home Discussion Lawn Care Advice FloraTam Lawns Controlling Weeds, Pests, Etc.

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    Ryan Curby

    The best approach to weed control is a healthy, vigorous lawn. Weed problems in a lawn indicate that the turf has been weakened by improper management practices or damage from pests. Proper management practices can eliminate many weed problems. If weeds are a persistent problem, herbicides labeled specifically for St. Augustinegrass should be used. If an herbicide is needed, preemergence herbicides (e.g., pendimethalin, benefin, bensulide, atrazine, or others) can be applied to control crabgrass if it was present in previous years. Timing is critical for successful control. As a general rule, preemergence herbicides for crabgrass should be applied February 1 in south Florida, February 15 in central Florida, and March 1 in north Florida. Note: Preemergence herbicides will not control weeds that are actively growing.

    Postemergence herbicides (e.g., atrazine) should be applied as needed for control of summer annual and perennial broadleaf or grassy weeds. These materials should not be applied if the turf is under moisture stress or when air temperatures exceed 85°F. Your local county Extension office can assist with weed identification and provide the latest recommendations.

    Many commercial “weed-n-feed” formulations provide control, but they should be used with caution because certain plant materials may not be tolerant. These herbicides can damage landscape plants whose roots may extend far under the lawn. These materials should only be used when a lawn has a uniform weed population. If weeds exist only on a portion of the lawn, “weed-n-feed” products should not be applied to the entire lawn. If the situation warrants the use of a “weed-n-feed” product, it is important to determine if the manufacturer’s recommended rate of application supplies the amount of fertilizer needed by the turfgrass and the amount of herbicide that is required for weed control. Supplemental applications of fertilizer or herbicide may be required if the fertilizer/herbicide product does not supply enough fertilizer to meet the fertility needs of the turfgrass or the amount of herbicide needed for weed control. Carefully read the label before use and follow all label directions. Refer to ENH884, Weed Management in Home Lawns (http://edis.ifas.ufl.edu/ep141) for more information.

    The major insect pest of St. Augustinegrass is the southern chinch bug (Figure 7). Chinch bugs are foliar-feeding insects that suck plant juices through a needlelike beak, causing yellowish to brownish patches in turf (Figure 8). Injured areas are usually first noticed as the weather begins to warm in areas along sidewalks, adjacent to buildings, and in other water-stressed areas where the grass is in full sun.

    Chinch Bugs
    Picture of Chinch Bugs

    Chinch Bug Damage
    Picture of Chinch Bug Damage

    Other insect pests, including webworms, armyworms, grass loopers and mole crickets can damage St. Augustinegrass. Mole crickets damage turfgrass areas primarily by creating tunnels or soft mounds while searching for food. Additional damage may result from small animals digging through the soil profile in search of the mole crickets as food. Check for mole crickets by examining an area for tunnels or by applying 2 gallons of water mixed with 1½ ounces of liquid detergent soap per 2 square feet in suspected damaged areas. Mole crickets will surface in several minutes.

    White grubs are another pest of St. Augustinegrass. These can be found by lifting the grass to a depth of about 2 inches. Grubs can be seen feeding on the roots at this level. For more information on insect control, refer to ENY300, Insect Pest Management on Turfgrass (http://edis.ifas.ufl.edu/ig001).

    Large patch (Figure 9) and gray leaf spot (Figure 10) are two major disease problems of St. Augustinegrass. Large patch occurs in warm, humid weather and is encouraged by excessive nitrogen. It is generally most noticeable during the spring and fall months. Gray leaf spot occurs during the summer rainy season and is primarily a problem on new growth. Both diseases can be controlled with fungicides.

    Large Patch Symptoms
    Large Patch Symptoms

    Gray Leaf Spot Symptoms
    Gray Leaf Spot Symptoms

    Other St. Augustinegrass disease problems originate in the root system. Take-all root rot (Gaeumannomyces graminis var. graminis) occurs under high moisture or stress conditions. When symptoms are noticeable aboveground, the disease is usually in an advanced stage. Following proper cultural practices is the best defense against this disease. Refer to SS-PLP-14, Turfgrass Disease Management (http://edis.ifas.ufl.edu/lh040), for more information.

    Several types of nematodes infest St. Augustinegrass lawns. Population peaks of nematodes typically occur in late April to early May and again in late August to early September. Damage symptoms (Figure 11) include thin stand density, less vigorous growth, a weakened root system, slow recovery following rain or irrigation application, and certain weeds such as prostrate spurge and Florida pusley. Plant parasitic nematode levels can be positively identified only through laboratory procedures. The local county Extension office can provide information on submitting soil samples to the University of Florida Nematode Assay Laboratory. There currently are no effective nematode controls for use on the home lawn. Cultural controls include encouraging deep turfgrass rooting by raising the mowing height, irrigating less frequently but more deeply, and providing ample soil potassium. For more information on nematodes, refer to ENY006, Nematode Management in Residential Lawns (http://edis.ifas.ufl.edu/ng039).

    Other Problems
    Other factors also can decrease the quality of a lawn. Excessive shade, compacted soils, over- or under-watering, improper mowing, traffic, and high or low pH all can cause a lawn to perform poorly. It is important to recognize the source of the problem and to correct it if possible. For more information on these types of stresses, refer to ENH153, Environmental Stresses and Your Florida Lawn (http://edis.ifas.ufl.edu/ep070).

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