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Update (4/27/2011)

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Does Wet + Cool = Turf Disease?

Weather

A brutal week for St. Louis and points south.  Rainfall totals of 6-12” are estimated for much of southern Missouri from last week’s storms, with 18” local amounts.  After a brief reprive during the week, additional rainfall is forecasted for the region over the weekend.  “April showers bring May flowers.”  Enough already. 

Temperatures are seasonably mild, and are anticipated to stay that way over the next 7 days.  Two-inch soil temperatures have steadied to mid 50’s for much of central Missouri and will stay there until we get a warm-up.  Because of this, preventive treatments for summer patch are still at least a week or more away for most of Missouri, except for the bootheel.   

Wet weather pattern mid April

Large Patch of Zoysia

A number of large patch reports have streamed in over the past few weeks on golf courses and home lawns.  Large patch outbreaks occur during the fall and spring on zoysia that is either going into or coming out of dormancy.  The disease is caused by a strain of Rhizoctonia solani, which makes it a kissing cousin to the more commonly known brown patch disease of cool season turf.  As the name implies, the key symptoms are large (nearly indefinite sized) patches of declined turf that are bordered by an intense orange or rust colored margin (termed “firing”) during periods of high pathogen activity.   The recent prolonged cool and wet weather is the perfect environment for this pathogen, and large patch has been especially severe this spring.

Large Patch active in Missouri

Integrated management of this disease includes providing adequate drainage and thatch management with cultivation practices.  However, it is extremely important not to aerify, or perhaps even mow, zoysia with large patch symptoms now because it will spread the pathogen to new areas.  Excessive nitrogen can also exacerbate the severity of the disease, so it is important not to fertilize zoysia now or in the fall after September 1 when the disease is likely to be active.  Fertilization of affected areas should resume in June, when temperatures rise and zoysia is actively growing and can recover.  Also pay particular attention to weed encroachment in affected areas, particularly by other warm season species such as bermudagrass.

Management of this disease with fungicides centers on preventive applications in the fall in September and October, so it is important to map out areas now so applications can be made as spot treatments and fungicide is not used unnecessarily.  For large areas such as golf courses, Google Earth or similar programs can be used to view the past history of the disease at the site.  The above figure shows satellite imagery from April of last year, and another online tool for measuring the affected areas can be found here by following this link -http://www.acme.com/planimeter/.  I have tested this tool vs. ground measurements on several plots at our research farm and have found it to be very accurate. 

Current recommendations are in a state of flux as we continue to unravel the biology of this disease, but strong brown patch fungicides such as Heritage, Insignia, Disarm, ProStar, or Bayleton have worked well preventively in field studies.  We are currently evaluating several other products at the research farm and on a local golf course fairway for large patch control.            

Pythium root rot – Only Needs a Pool to Swim In

It is commonly thought that Pythium on golf putting greens is only a problem during high temperatures.  This is may be true for some Pythium species, such as P. aphanidermatum, which causes a rapid foliar blight, but there are plenty of other species that occur during cooler temperatures when the soil is saturated (read: now).  Some pathologists argue that Pythium root rot not a true disease, and that saturated soils are in fact the sole cause of the root decline.  However, curative use of Pythium fungicides (i.e. Koban, Terrazole, Segway, Stellar) has been shown to alleviate symptoms, strongly indicating the Pythium spp. are a considerable factor in turf loss.

Differences in Pythium diseases

Symptoms of Pythium root rot include a general, irregular decline of the turf.  This is in sharp contrast to Pythium root dysfunction, which tends to occur in patches.  Pythium root dysfunction also tends to occur more readily in drier soils and on newer putting greens, as opposed to Pythium root rot which has one necessary condition – lots of moisture.  We currently have plenty of it.   

Those affected by last week’s rains should be on the lookout for Pythium root rot symptoms on putting greens, and if something looks fishy should send a sample in for diagnosis.  Due to its spotty nature, information on Pythium root rot control is limited.  If you have had a history of Pythium root rot issues, a preventive application such as Subdue Maxx, Banol, or Segway may be warranted.  If you need to apply curatively,  an initial application of ethazole (Koban, Terrazole) as a knockdown is thought to be most effective, followed by a preventive.     

Save the Date:  July 26, 2011

Make plans to join us at the University Missouri Turf & Ornamental Research Farm on July 26th for our annual field day!  We will be presenting the latest research on cultivar evaluations, pest controls, and management considerations for turf, trees, and woody ornamentals.  It’s a fine day and a fine way to interact with colleagues and your local Mizzou research team.

Lee Miller
Extension Turfgrass Pathologist
University of Missouri