Weather and Turf Diseases – Turfgrass Science at Purdue University

Weather and Turf Diseases

From a temperature perspective, weather patterns in the Midwest have returned to normal this spring.  I recall the 80 F days in March 2012, and all of the concerns about scheduling fungicide sprays.  Hopefully most turf managers have resisted the temptation (regardless of who or what is doing the tempting) to apply fungicides for early season dollar spot control this year.  Fungicides will be effective only if the pathogen is active, and Sclerotinia homoeocarpa becomes active when mild weather prevails—not yet, but we’re getting close!

I also think it is too early for a summer patch spray.  The decision rule suggests that applications targeted towards summer patch should be initiated when soil temperature (2” depth) is 65 F or greater for several days.  There is so much “fudge factor” there.  Little or no hard science went into developing the rule—it’s all empirical.  Keep in mind that the pathogen comes out of dormancy more like a dimmer switch than an “on-off” switch, so it will take a while to ramp up to speed.  We intend to conduct some summer patch trials this summer, so I hope to have something useful to report next year.   

I suspect that symptoms of yellow patch (aka, cool season brown patch) are apparent on bent/poa greens and surrounds.  The heavy rains during the week of April 12 will have aggravated the situation.  Last April, we established a fungicide trial in an area where a yellow patch outbreak was severe—as bad as I have seen it in 15 years or so.  The fungicides included Prostar, Heritage (representing QOI products), Banner Maxx (representing DMI products), Cleary 3336, a chlorothalonil, and an untreated check.  The plots were monitored closely for 4 weeks.  In terms of symptom reduction, there were no differences among treatments, including the unsprayed check.  However, as daily temperatures increased, and the superintendent applied supplemental N, symptoms in ALL plots disappeared within a week.  By June 1, there was no recognizable damage, cosmetic or otherwise, to the turf.

Rick Latin
Turfgrass Pathologist


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