My St. Augustine grass is... #152795 - Ask Extension

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My St. Augustine grass is... #152795

Asked September 15, 2013, 8:40 PM EDT

My St. Augustine grass is developing yellow places and I put some sulphur on the places and it seemed to help but the places are getting larger.  I don't believe it is lack of water.  What can I do?

Parker County Texas

Expert Response

St Augustine lawn turn yellow sometimes from a lack of fertilizer but can be caused by one or several of these reasons: 1.        Leaching nutrients from soil from too much water either rain or irrigation Solution is to cut back on irrigation frequency. Check the irrigation system to make sure it is working properly. Set the controller to cycle and soak, which means applying the same amount of water but with multiple start times. Check your owner’s manual or call the manufacturer’s customer service to find out how to do this.  We do not usually recommend fertilizing during water restrictions, particularly now that the temperature is so high. But if you use a pelleted slow release fertilizer and apply the fertilizer either early in the morning on the day you are allowed to water. Water that morning for a short time and then again that evening for a short time. This will start the process of watering the fertilizer into the roots zone. 2.       Compacted soil will create such tight soils that water and fertilizer never gets down to the root zone. The heavy clay soil in Tarrant county get compacted from regular use – mowing, watering and rain but kids and pets playing can add to the compaction. After construction, soil is very compacted. Aerate the lawn and then spread about ½ inch of compost across the lawn before the aerated holes fill in with expanding clay. Water in the compost. The air in the roots zone and the nutrients in the compost will help. You may want to do this again in the fall. 3.       Lawn diseases may be the cause but usually lawn disease problem is not an entire lawn. Lawn diseases usually start in one spot and then spread. 4.       Misapplication of weed killer.  Take-all Root Rot of Turfgrass Take-all root rot is a serious disease caused by the soil fungus Gaeumannomyces graminis var. graminis. Take-all root rot causes brown, dead areas to develop in turfgrass. The disease was first described in Texas in 1991 on St. Augustinegrass. Since then, it has been confirmed on bermudagrass (where it is often called bermudagrass decline), zoysiagrass and centipedegrass. Symptoms and diagnosis Symptoms of take-all root rot often are noticed first in spring or early summer, but may show up at any time during the growing season. The grass appears yellowish (chlorotic) thins out in large, irregular patches 1 foot to more than 20 feet in diameter. Individual grass blades do not separate easily from stolons (horizontal stems). The roots of infected grass are usually short, blackened and rotted. The stolons often can be lifted easily from the soil because of the poor root system. Nodes may be discolored. The yellowish foliage eventually dies and turns brown. Take-all root rot may be mistaken for Rhizoctonia brown patch or chinch bug injury on St. Augustinegrass. If you suspect your grass has take-all root rot, first eliminate the possibility of these other problems.   The fungus that causes take-all root rot is common in Texas, in both diseased and apparently healthy grass. It does not survive well in the soil without a host plant or plant debris, such as thatch. Turfgrass often shows the first symptoms of the disease from spring green-up through early summer, which suggests that the fungus infects the turf grass in the fall or early spring. However, the disease can occur at any time during the growing season, especially when the weather is warm and moist and grass is under stress. The disease is not spread by mowers or by normal traffic, but it can be spread by the movement of infected grass or infested soil.   Cultural disease management Controlling take-all root rot (and bermudagrass decline, as it is also known) requires both cultural and chemical practices. The first step in preventing the disease is to take proper care of the grass, so that it grows at a moderate rate and there is abundant microbial activity in the root zone. Good surface and subsurface drainage is important. Turf areas that remain wet are prone to disease. Improve drainage if necessary and fill in any depressions in the soil. Avoid over watering. It is better to water infrequently but deeply (6 to 8 inches deep) than to give the grass frequent, shallow waterings. Have your soil tested and fertilize grass on the basis of the test recommendations. Do not apply excessive rates of nitrogen fertilizer. If possible, adjust the soil pH in the root zone so that the pH is slightly acidic, preferably within the range of pH 6.0 - 6.8. To help adjust pH and control disease, spread about ½ inch of compost over the lawn in the spring and fall for several years. Soil also should be aerated if it is compacted. Fungicides If take-all root rot or bermudagrass decline are a problem in your lawn, you will probably need to apply a fungicide. Fall and spring are the best times to do this. The following fungicides are labeled for the control of take-all root rot or have been shown to be effective in research tests. Check with local garden centers and feed stores for a recommendation. Fungicide should be applied in a high volume of water or watered in thoroughly right after application. This will ensure that the product moves into the grass root zone rather than drying on the leaves. Common hose-end applicators work well for soaking the fungicide into the root zone. Fungicides are most effective as preventative treatments and much less effective after the disease has become well established. However, it is usually effective to treat diseased areas in the spring after the easily-removed, infected stolons are raked out or lifted away. Two applications 3 to 4 weeks apart may be required. Always read and follow carefully any instructions and precautions on the product label.   Take-all root rot usually becomes a serious problem only when turfgrass is under stress because of soil compaction, temperature extremes, herbicide injury, imbalanced soil fertility, excessive shade, improper mowing height or frequency, excessive and too frequent watering, or any other condition that weakens the turf.

Dotty Woodson Replied September 17, 2013, 10:31 PM EDT

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