St.Augustine Grass Nematodes

Nematodes

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 13) 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. Soil nematode levels can only be positively identified through laboratory procedures. The local county Extension office can provide information on submitting soil samples to the University of Florida Nematode Assay Laboratory. There are currently no effective nematode controls for use in 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).

 

Figure 13.Signs of nematode damage in St. Augustinegrass
[Click thumbnail to enlarge.]

 

Other Problems

Other factors can also decrease the quality of a lawn. Excessive shade, compacted soils, over- or underwatering, improper mowing, traffic, and high or low pH can all cause a lawn to perform poorly. It is important to recognize what the source of the problem is 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).

Thatch Removal

Thatch is the layer of undecomposed leaf blades, stolons, roots, and crowns intermingled with soil (Figure 14). Leaving mowing clippings on the lawn does not cause thatch because clippings are readily broken down by microbes in the soil. Thatch development is greatest in grass that is overfertilized or overwatered. An excessive thatch layer reduces water penetration and can bind up fertilizer or pesticides. In severe cases, roots may be seen actually growing aboveground and rooting into the thatch layer. This is a very unhealthy condition and leaves the lawn vulnerable to many stresses.

 

Figure 14.Thatch layers can develop in St. Augustinegrass, especially when fertilization or irrigation rates are high.
[Click thumbnail to enlarge.]

 

If the thatch layer exceeds 1 inch, it may be removed by vertical mowing, or “verticutting,” in early spring to midsummer. Verticutting uses vertical blades that slice through the thatch and slightly into the soil, resulting in much of the dead material being removed from the top of the lawn. A 3-inch spacing between the dethatching blades is best for St. Augustinegrass. Caution: Vertical mowing may result in damaged turf that requires a period of recuperation. Do not attempt vertical mowing unless the grass is actively growing. Verticut should be done in an east to west or north to south pattern, but not in all four directions. Debris should be removed by raking, sweeping, or vacuuming, followed by a conventional mowing to improve turf appearance and immediate irrigation to prevent root zone dehydration. One week after vertical mowing, fertilizer should be applied at the rate of 1 pound of nitrogen per 1000 square feet to encourage recovery. This material must be watered into the soil immediately following application to prevent plant burn. Periodic topdressing (adding a uniform layer of soil on top of the grass) with ¼ inch of soil similar to that underlying the turf is the best method to alleviate thatch accumulation; however, the physical labor required limits the practicality of this method for most homeowners. If topdressing, be sure to use soil that is free of weed seeds and nematodes and be careful not to exceed recommended topdressing rates, as this encourages large (brown) patch disease.

Renovation

Large, bare areas can be replanted by broadcasting sprigs (1 bushel per 1000 square feet), by planting 2-inch plugs every 12 inches, or by sodding. These areas should be kept continuously moist with light, frequent irrigations several times daily until runners develop or sod is well rooted. Over time, irrigation frequency should be gradually reduced, but duration should be increased to apply ½–¾ inch of water. Refer to ENH03, Establishing Your Florida Lawn (http://edis.ifas.ufl.edu/lh013), for more information.

Tables

Table 1.Relative growth characteristics for St. Augustinegrass cultivars

Cultivars

Mowing height (inches)

Cold tolerance

Shade tolerance

Chinch bug resistance

Green color

Texture

‘Bitterblue’

3.5–4

Good

Good

Slight

Dark

Coarse

‘Classic’

3.5–4

Good

Medium

Unknown

Dark

Coarse

‘DeltaShade’

3.5–4

Good

Good

Unknown

Good

Coarse

‘Floratam’

3.5–4

Poor

Fair

Slight

Dark

Coarse

‘Floralawn’

3.5–4

Poor

Fair

Slight

Dark

Coarse

‘Palmetto’

3–4

Fair

Fair

Unknown

Lighter green

Fine

‘Raleigh’

3–4

Very good

Medium

Poor

Medium

Coarse

‘Sapphire’

2–2.5

Unknown

Unknown

Unknown

Medium

Coarse

‘Captiva’

2–2.5

Good

Good

Good

Dark

Fine

‘Delmar’

2–2.5

Good

Good

Poor

Dark

Fine

‘Seville’

2–2.5

Fair

Good

Slight

Dark

Fine

Table 2.Annual fertilization recommendations for St. Augustinegrass in three regions of Florida

Location1

N fertility guideline

(lbs N/1000 sq ft/year)

North Florida

2–4

Central Florida

2–5

South Florida

4–6

1North Florida in this example is considered to be anything north of Ocala. Central Florida is defined as anything south of Ocala to a line extending from Vero Beach to Tampa. South Florida includes the remaining southern portion of the state.

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Footnotes

1.

This document is ENH5, one of a series of the Environmental Horticulture Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date May 1991. Revised April 2011. Visit the EDIS website at http://edis.ifas.ufl.edu.

 

2.

L. E. Trenholm, associate professor, turfgrass specialist, Department of Environmental Horticulture, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611; J. L. Cisar, professor, turfgrass specialist, Ft. Lauderdale Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida, Ft. Lauderdale, FL 33314; and J. B. Unruh, professor, turfgrass specialist, West Florida Research and Education Center, Institute of Food and Agricultural Sciences, Jay, FL 32565.

 


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