by Larry Williams, UF/IFAS Horticulture Agent
Take-all root rot is a disease that often affects our Florida lawns this time of year. Rainy weather can trigger this disease.
The name take-all is descriptive in that this native soil-borne fungus, Gaeumannomyces graminis var. graminis, can result in relatively large areas of a lawn dying down to bare ground. This pathogen affects all warm-season turfgrasses.
Managing a lawn to prevent this disease is important. This includes mowing at the correct height for the type of grass you have. Lawns do best when the sprinkler system is set on manual. Irrigating daily for a few minutes is not beneficial for a lawn but does benefit turfgrass pathogens. Irrigate when dew is present, usually between 2 and 8 a.m. and only apply enough water to saturate the lawn’s root zone. It is important to use a fertilizer program that provides equal amounts of nitrogen and potassium. Most homeowners use lawn fertilizers with too much nitrogen and too little potassium. Acidifying fertilizers such as ammonium sulfate or slow-release urea products may be helpful. Heavy liming has 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. Fungicides may be useful but only when used preventatively, applied weeks or months in advance of above-ground symptom development. Without eliminating the plant stresses via cultural control methods, fungicides will have minimal effects.
Below are key points concerning this disease taken from the UF/IFAS Extension publication “Take-all Root Rot” (http://edis.ifas.ufl.edu/pdffiles/LH/LH07900.pdf).
- High rainfall and stressed turfgrass trigger the disease.
- By the time aboveground symptoms appear, the pathogen has been active on the roots for at least two to three weeks—probably longer.
- The turfgrass must be mowed at the correct height.
- Nitrogen applications should be balanced with equal amounts of potassium. For every pound of nitrogen applied, an equal amount of elemental potassium should be applied.
- Nitrate-nitrogen products and quick-release urea products (e.g., uncoated urea) should be avoided.
- Extra potassium may be useful in late summer and early fall.
- Fungicides are best used preventively, meaning they must be applied prior to symptom development.
Since recovery of take-all damaged turf is usually poor, complete renovation of diseased areas of a lawn may be necessary.
As a native, soil-inhabiting fungus, take-all root rot cannot be eliminated. But suppression of the pathogen through physical removal, followed by correct management of the new sod is critical to establishing a new lawn.
Correct lawn management practices, not chemicals, offer the best control of this common lawn disease.