Root Rot in St. Augustine Lawns

Root Rot in St. Augustine Lawns

Take-All –Root rot in St. Augustine lawns

The past few years have been rough on St. Augustine lawns in this area. Summer drought, weeks of winter rain and freezing temperatures below average, all this has taken its toll. Where I work we have had numerous calls concerning poor looking turf with panicked home owners wanting something to put on the lawn to make everything better.  Unfortunately there is not an easy answer or a guaranteed cure.  St. Augustine is susceptible to over a dozen diseases; most are mild and easily controlled or managed. The one that has emerged at the top as the most troublesome to control is commonly called Take-All or Take-All-Root rot. The scientific name for it is a long one, Gaeumannomyces graminis var. graminis. This disease will attack seemingly healthy turf and will move rapidly through stressed or weakened turf.  All varieties of St. Augustine are susceptible; there is no resistant variety at this time. The disease can affect other turf grasses such as Bermuda, Zoysia and Centipede grass. The disease has been documented in Texas, Florida, Alabama and California.

This spring St. Augustine lawns are showing damage done by both fungus and cold.  I have seen one lawn be almost completely green and the one right next door or across the street have moderate to severe damage. It also appears that lawns with the fungus going into the winter may have been more susceptible to cold damage for the simple fact that the turf was already weakened by disease and was not strong enough to take the extra stress of cold. Many people mistake the cold damage for fungus damage, grub damage or even chinch bug damage. I will cover what to look for in fungus damage later in this article but it is too early in the season for chinch bugs and grub damage. If the damage had been caused by either of these two pests if would have had to happened before the lawn went into winter. The damage cause by chinch bugs and grubs generally will show up in summer or fall when they are active; neither is active in cold weather.

There are many diseases that mar St. Augustine turf and all can weaken it but generally do not kill it out right, but it is this weakness that can make Take-All more devastating. The best preventative measures that I can recommend are to keep the lawn as healthy as possible. Mow consistently, do not let the turf overgrow and shave it off. Water as needed, do not over water, but try to not let it get too stressed in hot dry conditions by applying the recommended amount of water for your soil type and area. If you are still not certain about water, talk it over with a master gardener or someone in the county extension office.  Fertilize as needed with a good quality lawn food that is a slow release formula. Do not use fast acting, quick release fertilizers if at all possible.  Most lawn foods have some immediate release nitrogen in them that is fine; you do not want it to be the largest percentage of what you are using. If you are unsure contact the extension agent’s office for a soil test kit.  One other point to consider when feeding a lawn stressed by insect or disease damage: be very careful when using fertilizers containing weed killing agents or weed prevention products; both can be very stressful to turf that is already weak and may damage it more. Read the label to see what restrictions may apply and do not keep asking the garden center employees for the answer you want to hear instead of what you need to hear.  It may come down to a choice of do I put up with some weeds or try to save my turf.

If you have a heavy clay soil consider having the lawn aerated using a service or machine that will pull a plug of soil out and leave it on the surface. The other punch types leave a hole but compress the soil to make that hole. After this is done that is an excellent time to apply fungicide granules, slow acting fertilizers or the peat moss.

As stated before, there are many diseases that can kill or weaken St. Augustine turf, but Take-All has a very distinct habit. The general pattern in the affected turf may vary slightly, but overall it is the same. The disease starts out as a yellowing of the turf that can be a few leaves here and there scattered around the lawn or a specific area, or it can be in streaks like someone has slung yellow paint across the area. At other times it can appear to be “flowing” across an area or it can be in a ring like pattern with dying turf at the center. The one constant in all this is the yellowing that precedes the death of the turf inside the area of yellowing grass blades. Sometimes the turf may die quickly, other times it my go away slowly. Take-All is a soil disease and works by attacking the roots of the turf, causing the turf to lose vigor and generally not grow as well. This is why it is sometimes mistaken for grub damage due to the fact that the roots are gone and the turf pulls up easier. Other times the yellowing is mistaken for the need to fertilize or add iron the lawn; those needs are displayed by a general off color in the turf, not by clearly defined spots or blotches in the lawn.  If you are still unsure contact a certified nursery professional or a master gardener to have it verified.

Once the disease has been diagnosed, there are not many options for the control of it. A few chemical fungicides list the disease on their label, most are a systemic form of lawn chemical and will have limited effect depending on the severity of the disease in the turf. Sometimes you may be able to achieve a good control of the outbreak and other times not, but always read the label first and follow recommended application. Most chemicals can be somewhat expensive, so do not try to save money by skimping on the rate of application. If you do not use enough product, you are wasting your money and time. The other approach to controlling the disease is with the use of Canadian Brown Sphagnum Peat Moss. This is a naturally acidic and organic product that seems to control or inhibit the disease by changing the acidity of the soil and adding organic elements to the soil. When applying the peat do not rake the area too aggressively; the Take-All causes the roots of the turf to rot and become brittle so raking too much can cause even more damage to the already weakened turf.  The peat is applied at a rate ranging from ¼ of an inch to as much as ¾ of an inch in depth.  A bale that is 3.8 cubic feet in size will treat an area of about 1,000 square feet. There is no easy way to apply it other than with your hands or a shovel then gently working it down into the turf so that the turf is not covered up; the grass needs to be able to get sunlight. Then water thoroughly; the peat will not work if left dry. It must be soaked in and watered regularly. There are other soil acidification products out there on the market and some homeowners have had fair results with them, you may wish to use a combination of products to treat the disease.

I cannot offer a statement of use this or use that or do this or do that and everything will be wonderful and all your problems will be solved. This disease is a soil fungus and there is not a product on the market that will wipe it out.  Depending on the season, the weather and the general health of the turf, some years the disease will be worse than others. Like the common cold, all you can do is treat the symptoms as they appear and do your best to keep the lawn healthy in between. As I stated earlier there are not varieties of St. Augustine turf that are more resistant or immune to Take-All. Re-sodding is only an option if you have lost the turf in an area. Removing the old turf and placing new turf will not remove the disease. It is in the soil. I do not intend to sound negative, but like a good doctor I want to give you facts and options, not rosy unrealistic promises. St. Augustine is still a very good choice for lawns in this area and it is in no way about to go away. Depending on your situation there are other options out there to explore. Happy Gardening!

Mark Barnett

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