Rapid Blight Fungicides

Rapid blight is a disease of salt-stressed cool-season turf caused by Labyrinthula terrestris. It is most common where reclaimed or otherwise saline irrigation water is used.

What to Look For

Affected turf yellows, bronzes, and dies in irregular patches. Fall overseedings may fail before or after emergence, and damage can be confused with direct salt injury.

Why It Develops

Elevated irrigation-water salinity, sodium accumulation, inadequate leaching, poor infiltration, and salt-sensitive grasses create the conditions needed for disease.

Reduce Disease Pressure

• Test irrigation water and soil salinity.
• Improve infiltration and leach salts below the root zone when water quality and drainage allow.
• Blend or replace high-salinity water where practical.
• Use more salt-tolerant turf species or cultivars in chronic sites.

What University Research and Extension Guidance Says

University of Arizona research established the close connection between rapid blight and saline irrigation and developed assays that correlate with field trials for screening fungicides and turf varieties. Fungicides may suppress the pathogen, but salinity management is the foundation of control.

Choosing and Using a Fungicide

Use the products below as a starting point, then match the active ingredient, FRAC group, turf species, use site, timing, rate, interval, and watering directions to the current product label. Preventive or very early applications are usually more reliable than rescue treatments after extensive injury. Rotate effective FRAC groups and combine fungicides with the cultural changes above.

Research and label note: University research may identify useful activity even when a current product label does not name this disease. That is research evidence, not a label direction. Apply a product only where the turf or application site and use pattern are permitted, and follow the complete label and applicable state requirements.

University sources: University of Arizona: Rapid Blight Fungicide Efficacy Research; University of Arizona: Salinity Problems in Turf.