The following is from of a University of Florida publication on the care of St.Augustine Grass lawns.
JUNE - AUGUST
Mowing: Mow at 3 inches (as high as possible with a home rotary mower) on low-maintenance lawns or 2½ inches on higher-maintained ones. Use only a sharp, balanced mower blade and return clippings on the lawn unless the amount is excessive and clumping occurs. If clippings are excessive, allow them to dry in the sun and scatter them by remowing, blowing, or raking.
Fertilization: Fertilize with 1 pound of nitrogen per 1000 square feet (e.g., 1 pound nitrogen = 6.5 pounds 15–0–14 or 6.25 pounds 16–4–8 per 1000 square feet) in early July for higher-maintained areas. A slow release nitrogen source (e.g., IBDU, milorganite, SCU, urea formaldehyde, poly-coating sources) will extend nitrogen response and discourage rapid flushes of growth or nitrogen loss due to excessive rainfall.
Using an iron source during summer is an alternate recommendation to nitrogen to provide desirable dark color without undesirable flush of growth. Using a quick-release nitrogen or water soluble nitrogen source at this time may encourage chinch bugs or disease development. Fertilizers without phosphorus (e.g., 15–0–14, 8–0–24) are acceptable during this time if soil tests indicate moderate to high levels of soil phosphorus.
If excessive yellowing occurs, supplemental iron applications may be required. Refer to the fertilization for "February - May" section for information on iron application. Check for manganese deficiency as mentioned previously.
Irrigation: May is still dry, so water thoroughly on your watering days. For the summer months though frequent, intense rainfall normally occurs during this period. Therefore, irrigate to prevent drought stress only on an as-needed basis. Apply water (¾ inch) as previously noted, and then wait until the turf shows signs of wilting (blue-gray color or footprinting occurs) before irrigating again.
Weed Control: The best method to control weeds is through a healthy, vigorous turf. Applying any postemergence herbicides during summer may result in objectionable turf injury. St. Augustinegrass is damaged by certain herbicides (e.g., MSMA, DSMA). Follow label directions and use with caution. Do not apply herbicides unless grass and weeds are actively growing and not suffering from drought stress and air temperatures are below 85°F.
Insect Control: Check for chinch bugs by the previously described method. If the turf turns yellow in spots or responds poorly to watering and fertilization, suspect root damage from white grubs. Check for white grubs (root feeders) by cutting three sides of a 1-foot square piece of sod about 2 inches deep with a spade/shovel at the edge of one of the yellow areas in the lawn. Lay back the sod and check for white C-shaped grubs. Apply an insecticide if two or three grubs are found per square foot.
Check for additional insects such as armyworms, sod webworms and mole crickets by mixing 1 to 2 ounces of dishwashing soap in a 2- gallon sprinkling can full of water. Drench a 2 square foot area with this solution. If insects are present, they will surface in several minutes.
Read and follow all pesticide labels.
Disease Control: Important disease symptoms are usually expressed as circular brown patches one to several feet in diameter or by spots (lesions) yellow, brown or purplish in color on individual leaves (gray leaf spot disease). Many times these result from overirrigation or excessive nitrogen fertilization. Therefore, reduce the amounts of these applied. If damage is extensive, a fungicide application may be necessary.
-->Refer to your local county Cooperative Extension Service office for disease sample submission and the latest fungicide recommendations.