Dr. Kevin Korus: Please don’t ‘take-all’ of my turfgrass
There are many different insect pests, pathogens and abiotic stresses that can cause turfgrass to underperform or even die off. It can be quite difficult to identify the cause of your turf’s stress, and consulting a lawn care specialist or submitting a sample to a plant disease clinic may be necessary to confirm the cause of dieback. It is important to confirm the cause of stress so that you can tailor your management plan to treat the correct issue. The correct management strategy cannot be implemented until the correct diagnosis is made.
One turf disease, take-all root rot, caused by the fungus Gaeumannomyces graminis var. graminis, tends to appear this time of year when temperatures are high and the turf receives excessive amounts of rainfall or irrigation. Take-all root rot can be an issue with several different turfgrass species; however, St. Augustine grass is particularly susceptible. The fungus infects the roots and stolons of St. Augustine grass but not the leaves. Turf infected with take-all root rot will initially develop yellow or light-green patches. These patches eventually turn brown, and the grass dies all together. Weeds often replace the turf in these areas. Grass roots will be underdeveloped and appear dark brown or black. Stolons will contain dark brown, sunken lesions and will eventually die all together. Take-all root rot will not cause lesions on the leaf or leaf sheaths.
It is extremely difficult to “cure” this disease, so prevention is your best bet. Turf should be properly fertilized and mowed frequently enough so that only 1/3 of the leaf tissue is being removed with each cutting. It is encouraged to take soil samples from your turf area so that a pH of around 5.5 is maintained. Over-irrigating, coupled with plant stress, is the No. 1 cause of take-all root rot. One mistake that homeowners make with turfgrass irrigation is that when they have automatic systems, they will set it and forget it. Turfgrass needs different levels of irrigation depending on the time of year and amount of rainfall received. For proper irrigation recommendations for turfgrass, please consult the UF/IFAS EDIS document ENH9, Watering Your Florida Lawn (edis.ifas.ufl.edu/lh025).
The fungus responsible for this disease is soilborne. This means that if you replace the dead turf in your yard, the new, healthy turf will eventually get the disease as well. The fungus must be removed from the soil via the application of fungicides or through soil heat sterilization. When selecting a turfgrass fungicide, make sure that the product is labeled for the control of take-all. Most turfgrass fungicides are developed for the control of leaf blight fungi; these products will not be effective against take-all. For this disease, you will need a product that moves systematically through the plant and has some soil residual. Fungicides that are labeled for the control of take-all root rot are most effective when applied in a preventative manner. You can achieve some curative control, but it is limited. Fungicide active ingredients that work best for take-all include azoxystrobin, myclobutanil, propiconazole, pyraclostrobin, thiophanate methyl and triadimefon.
For more information on take-all root rot, please refer to UF/IFAS EDIS document SS-PLP-16, Take-all Root Rot (edis.ifas.ufl.edu/pdf/LH/LH07900/pdf).
— Dr. Kevin Korus is the Agriculture and Natural Resources Extension Agent for UF/IFAS Extension Alachua County. Contact him at kkorus@ufl.edu or 955-2402.
This article originally appeared on The Gainesville Sun: Dr. Kevin Korus: Please don’t ‘take-all’ of my turfgrass
