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Rapid Blight in the West

Rapid blight continues to be a problem for us in the west - year round on annual bluegrass in California, in the spring and fall on annual and rough bluegrass in Nevada and during the fall overseed on rough bluegrass and perennial ryegrass in Arizona.

A few weeks ago - working with Colorado State University's Tony Koski and Ted Tisserat, we confirmed the first incidence of this disease in Colorado on a course where it had caused significant damage to 9 annual bluegrass greens. The damage was most evident after a spring blizzard and we suspect that irrigation water high in sodium accumulated from winter snow melt is to blame.

The take home message here is that this pathogen can pop up and cause problems when salt levels are elevated on cool season turf and rapid blight is likely more widespread than we'd like to be. Unfortunately - this disease is hard to diagnose without a microscope and assistance from a diagnostic laboratory is needed.

One of the most effective tools that can be used to control this disease is just monitoring soil salinity levels with a handheld TDS meter, such as the Oakton EC tester - readings above 0.6 mS/m in the upper inch of moist soil and thatch (equivalent to 2.4 dS/m based on saturated paste extract analysis) often indicate you are at salinity levels conducive for the development of this disease.

Basically, monitoring is performed by wetting the area with potable, fresh water and jamming the probe into the soil and thatch under the canopy.

Work by Mary Olsen at Unversity of Arizona has shown that the rapid blight pathogen grows best at sodium levels above 2 dS/m (1280 ppm) and that sodium is the primary salt that is needed. Other cations like calcium and potassium don't appear to have an effect on the pathogen. Leaching sodium out of soils with adequate water and calcium (to displace sodium in the system) is the 'cure' for rapid blight. Fungicides like mancozeb, Compass and Insignia are effective in halting the disease, but often the disease will return if salt levels are high.

For more information on this disease - check out the excellent review article on rapid blight avaliable here:

Signing off from the left coast - see you next week!

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