Understanding your Lawn: St. Augustine Grass By Mario Villarino

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Understanding your lawn: St Augustine grass

As our temperatures steadily increase and maintain temperatures, so is our desire and interest in the garden and lawns. After last weekend, the consultations coming to the extension offices related to lawn issues increased significantly. Common questions related St. Augustine grass lawns. St Agustine grass (Stenotaphrum secundatum (Walt.) Kuntze), is a perennial robust grass widely used for pastures and lawns. In the warmer climates of the tropics and subtropics it rivals bermudagrass in importance. St. Augustine grass is adapted to moist, coastal areas with mild winter temperatures. It is known to be tolerant of high summer temperatures, and St. Augustine grass retains its color at temperatures as much as 10° lower than those which discolor bermudagrass.

St. Augustine grass tolerates moderate shade, being as good or better than other warm season grasses for shaded sites. However, under densely shaded conditions, St. Augustine grass develops thin, spindly turf. So long as fertility and drainage are adequate, St. Augustine grass tolerates a wide range of soil types. St. Augustine grass grows satisfactorily at a pH range from 5.0 to 8.5, but develops a chlorotic appearance in highly alkaline soils (above pH 7.5). It does not tolerate compacted or waterlogged soil conditions. St. Augustine grass is highly tolerant of soil salinity, producing satisfactory growth at salt levels as high as 16 mmhos. Bermudagrass will tolerate only slightly higher salt levels.

St. Augustine grass is used primarily for lawns as it does not tolerant traffic as well as some other warm season species. It produces satisfactory turf at moderate levels of maintenance, effectively competes with weeds and other grasses and has only a few serious pests. After establishment the success of St. Augustine grass as a lawn grass depends largely on management. Mowing, fertilization and supplemental watering are required to maintain a dense, green, weed-free turf of St. Augustine grass. The growth rate of St. Augustine grass is dependent on temperature, moisture availability and nutrient availability. Any one of these factors can limit the rate of growth of this species. In the spring with mild daytime temperatures and cool night temperatures, St. Augustine grass greens up, but makes little growth. As day and night temperatures increase during late spring and summer, the growth rate increases.

Thus, an established turf of St. Augustine grass may require mowing every 2 weeks in early spring and as often as every five days by late spring if nitrogen fertilizer is applied. St. Augustine grass is responsive to nitrogen fertilizer in terms of color and growth rate. On sandy soils St. Augustine grass requires about 1 pound of nitrogen per 1,000 square feet per month during the growing season to maintain satisfactory color and density. At rates above 1 pound per 1,000 square feet, St. Augustine grass produces lush growth that is highly susceptible to insects and diseases. On heavier textured soils 1/2 pound of nitrogen every month is adequate to maintain good color and growth. Thatch accumulation is also a problem when nitrogen fertilization exceeds the required rate.

Pests. Several insect pests cause serious damage to St. Augustine grass lawns. The Southern lawn chinch bug is the most serious pest on St. Augustine grass where the insect if active most of the year. In other states it ranks among the most serious pests along with SAD, brownpatch and white grub.

Timely applications of insecticides will control chinch bugs. Two or more treatments are required during the growing season in most areas, and as many as 5 or 6 may be required in some areas. White grub are also a serious pest on St. Augustine grass lawns. The grubs are the larvae of the May beetle or June bug that develop in the summer and fall just below the soil surface. The grubs feed on roots of St. Augustine grass and cause significant losses of turf during some years.

Damage usually appears the following year as dead areas of grass that can be easily lifted from the lawn. Grub control is difficult since the larvae are often quite large when detected and feed below the soil surface. Also, for them to be effective, insecticides must be drenched into the soil where the insects feed. Since some insecticides are tightly bound to the thatch layer of St. Augustine grass, drenching the material into the soil is difficult.

St. Augustine grass is susceptible to a number of turfgrass diseases including brownpatch, SAD, gray leaf spot, Helminthosporium, Pythium, rust, downy mildew and others. All of these diseases, except SAD, are caused by fungi and can be controlled by good management and fungicides. SAD is a virus disease for which there is no chemical control. Only resistant varieties of St. Augustine grass are effective against this disease. Floratam, Seville, Raleigh and several experimental varieties have shown good resistance to the SAD virus.

Brownpatch and gray leaf spot are the most serious diseases caused by fungi attacking St. Augustine grass. Although these diseases rarely kill St. Augustine, they severely weaken and thin the grass to the degree that the lawn is unsightly. Preventive applications of fungicides are most effective against these diseases.

A healthy St. Augustine grass lawn effectively crowds out most weeds. But St. Augustine grass that is not properly maintained or is weakened by insects or disease can be invaded by grassy and broadleaved weeds. Cool season weeds such as henbit, chickweed and clover are a serious problem in dormant St. Augustine grass. These weeds can be controlled by hormone-type herbicides in early spring.

Annual grassy weeds such as fescue, annual bluegrass and crabgrass are best controlled by timely applications of preemergence herbicides. Perennial grasses such as dallisgrass and bermudagrass are difficult to control in St. Augustine grass turf. Nonselective products can be applied as directed sprays to these weeds to obtain control. For more information on this or any other agricultural topic, please contact the Hopkins County Extension Office at 903-885-3443 or email [email protected].

Coming UP

Basic Vegetable Training with the Hopkins County Master Gardeners, Tuesday April 24, 2018 at the Hopkins County Extension Office 7:00 to 9:00 PM. $10 at the door.

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Mario Villarino DVM, Ph.D.
Hopkins County Extension Agent for Ag and NR
1200B Houston Street
Sulphur Springs, Texas 75482

Author: Savannah Everett

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