Managing Gray Leaf Spot on Perennial Ryegrass

Bruce B. Clarke

Rutgers University

Gray Leaf Spot

٠Causal agent: Pyricularia oryzae (teleomorph Magnaporthe grisea)

٠Susceptible turfgrass species: ٠St. Augustinegrass ٠perennial ryegrass ٠annual ryegrass٠tall fescue ٠kikuyugrass

GLS in CA 2003

• Almost 30 courses with positive diagnoses –mainly perennial ryegrass

• 1st epidemic: § August – September

• 2nd epidemic § October – November

GLS on Kikuyugrass (Pennisetum clandestinum)

Frank Wong

Frank Wong

Conditions Favoring Gray Leaf Spot

¹ 70º - 90 ºF Day Temp

¹Optimum when night temp > 70 ºF Temp

¹ High Humidity, young turf (4-5 weeks)

¹ Prolonged Leaf Wetness (9-24 hrs)

¹South-Facing Slopes without Shade

¹High Cutting Ht , High Nitrogen

Gray Leaf Spot Results

Nitrogen Study

CONCLUSIONS :v Severity of GLS typically increases with increasing

nitrogen (N) rate above 0.25 lb N 1000 ft2

v N source has been reported to affect GLS inPRG and TF, but not SA

v Compared to controls- water-soluble N sources increase GLS severity - slow release N sources may reduce the disease

v GLS appears to be more severe @ lower pH (<6.5)(e.g., Unlike summer patch, ammonium sulfate increases GLS)

Gray Leaf Spot Results

Cutting Height Study

Gray Leaf Spot Results

v Clipping Removal Study

Cultural Practices for Minimizing Gray Leaf Spot Pressure in Perennial Ryegrass

v Nitrogen should be avoided in summer, but if necessary, use no more than 0.1 to 0.25 lb nitrogen / 1000 sq ft / application

v Avoid acidifying and quick release sourcesv Don’t irrigate as dusk approaches.v Maintain a standard mowing height in fairways.vRemove clippings.vDelay overseeding until mid- to late – September.

Gray Leaf Spot Results

Developing Cultivar with Improved Tolerance to

Gray Leaf Spot

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1 2 3 4 5 6 7 8 9Gray Leaf Spot Rating (1-9 scale)

Mean = 4.7s.d. = 1.6

Mean = 6.8s.d. = 1.2

2000 Pop 2001 Pop Mean of selected parents

Population distribution of gray leaf spot resistance in perennial ryegrass populations comparing unselected populations with

selected populations.

Cycles of Selection for Gray Leaf Spot Resistance

OriginalC1C2Original C1 C2

The first Gray Leaf Spot resistant cultivars were sold in 2003

‘Ph D’ Blend ‘Paragon GLR’

Dramatic Improvements in Gray Leaf Spot Resistance over the past 5 Years

Perennial Ryegrass Cultivars with Improved Resistance to Gray Leaf Spot - 2007 (FS 1048 turf.rutgers.edu/)

1G2

1G2All*Star 3Apple GLCharismatic I GLSRDartDerby XtremeDP – 1 (Soprano)Exacta II GLSR*Fiesta 4*GL – 2HarrierManhattan 5 GLRPalace

Palmer IVPalmer VPalmer GLSPanther GLSParagon GLRPrelude GLSPrimaryProtégé GLRRegal 5Repel GLSRevenge GLXSecretariat II GLSRSR 4600Stellar GL

Gray Leaf Spot Control on Perennial Ryegrass: Rutgers 2007 (14-d)

Turf

Are

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Gray Leaf Spot Control and on PRG :

Daconil (top) , Heritage + Daconil (middle), Heritage (bottom)

Gray Leaf Spot Control on Perennial Ryegrass: Rutgers 2008 (14-d)

Turf

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fect

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CONCLUSIONS, cont.

v Fungicides:- most effective when used preventively- QoIs (Heritage, Insignia, Disarm) and

thiophanate- methyl are most efficacious

- DMIs (Banner) and chlorothalonil (Daconil) often provide good to excellent control under moderate pressure

- QoI + cholorthalonil (Renown) or QoI + DMI (Headway) have consistently provided the best control under high disease pressure