Last summer’s heavy rain and stress from January’s icy weather have contributed to widespread take-all root rot.
The culprit? A soil-inhabiting fungus — Gaeumannomyces graminis var. graminis — that causes leaf color loss and yellow grass patches ranging from a few inches to more than 15 feet in diameter.
Symptoms appear in the spring, but the disease can persist all summer and survive winter. Over time, the entire area dies as the root system rots away.
When disease occurs, raise the cutting height. Scalping grass damages the growing point; raising cutting height increases the green plant tissue available for photosynthesis, resulting in more energy for turfgrass growth and subsequent disease recovery.
If an area of the lawn has an active fungus, washing or blowing off the mower after use will reduce the disease's spread to unaffected areas.
The amount of water and timing of its application can prevent or contribute to disease development. Most fungal pathogens that cause leaf diseases require free water — rainfall, irrigation, dew — on the leaf to initiate the infection process.
Still, irrigating daily for a few minutes is not beneficial for turfgrass — it does not provide enough water to the root zone — but it does benefit turfgrass pathogens. So you should irrigate when dew is present, usually between 2 and 8 a.m., and only apply enough water to saturate the turfgrass' root zone.
Excessively high nitrogen fertility contributes to turfgrass diseases, so you should apply the minimum amount required for the grass species.
Potassium (K), key in disease prevention, prevents plant stress. Applying equal amounts of nitrogen and potassium is recommended for turfgrass health.
When disease damages turfgrass roots, it is beneficial to apply nutrients in a liquid solution. However, nitrate-nitrogen increases diseases' severity, so avoid its use when possible. Ammonium-containing fertilizers are preferred nitrogen sources.
Heavy liming has also been linked to take-all root rot increase. Since most turfgrasses can tolerate a range of pH, maintaining soil at 5.5 to 6.0 can suppress the pathogen's development. When the disease is active, frequent foliar applications of small amounts of nutrients is necessary to keep the turfgrass from declining.
Additional maintenance practices are thatch removal and reduction of soil compaction.
Applying azoxystrobin, fenarimol, myclobutanil, propiconazole, pyraclostrobin, thiophate methyl and triadimefon and excessively irrigating newly laid sod can help prevent disease development.
Ideally, the turf area should be mowed and irrigated prior to fungicide application. Unless the product needs to be watered in, do not irrigate for at least 24 hours after a chemical treatment.
Do not mow at least 24 hours to avoid removal of the product attached to leaf blades.
Since recovery of take-all damaged turfgrass is often poor, complete renovation of the lawn may be necessary. Removal of all diseased tissue is advised. As a native, soil-inhabiting pathogen, take-all root-rot cannot be eliminated. But suppression of the organism through physical removal, followed by proper cultivation of the new sod, is critical to establishing a new lawn.
Turfgrass management practices, not chemicals, offer the best control of the disease.
Sheila Dunning is an agent at the University of Florida's Extension office in Crestview.