Short Course - Diseases of TurfLane Tredway & Lee ButlerDept. of Plant PathologyNorth Carolina State University
What is a disease?An abnormality in structure or functioncaused by a long-term association with an infectious agentthat injures the plant or reduces its economic value
Turfgrasses are Susceptible to Disease when STRESSED
Some diseases caused widespread damage in a short period of time...
...others might reduce the uniformity of a playing surface...
...others may reduce the aesthetic appearance of the turf.
Injury is caused by humans or non-living factors.
Three factors are required for disease to develop t en nm Ho o st vir Disease En Pathogen
Five types of microorganisms cause disease Fungi (1X) Nematodes (400X) Bacteria (2,500X) Mollicutes (25,000X) Viruses (36,000X)
Number of Known Diseases by Pathogen Type Mycoplasmas Viruses Bacteria Nematodes Fungi
Percent of Turf Problems by Pathogen Type Nematodes Fungi
Nematode ClassiﬁcationNematodes are grouped by type of symptom induced, or uniquecharacteristic of nematode • Sting • Lesion • Lance • Ring • Stubby root • Spiral • Cyst • Root knot
The sting nematode is most damaging to turfgrasses.
Nematode damage is more severe in sandy soils.
Reduction of root depth is the most obvious symptom of nematode injury.
Diseases attack the turf in different locations Foliar Diseases: Copper spot Bipolaris & Drechslera leaf spots Brown patch Dollar spot Gray leaf spot Gray snow mold Stripe smut Pink patchStem and Crown Pink snow moldDiseases: Powdery mildewAnthracnose basal rot Pythium blightAlgae Red threadBentgrass dead spot RustsLarge patch Southern blightMelting out Yellow tuftWhite patch Root diseases: Bermudagrass decline Necrotic ring spot Pythium root dysfunction Pythium root rot Spring dead spot Summer patch Take-all patch
Mycology 101: Key Characteristics of Fungi• need water or high humidity to grow• grow and cause disease in a narrow temperature range• ubiquitous - they are everywhere!• primary role in nature is decomposition• some able to use a living plant as a food source
Most pathogens are facultative saprophytes, surviving in the thatch and soil when not causing disease
Hyphae are the basic vegetative structure of most fungi.
Masses of hyphae, visible to the naked eye, are called mycelium.
Some fungi produce spores directly on the leaf surface, whileothers produce them inside of special structures.
The Environment Triggers Disease Development• Weather – temperature, rain, humidity, dew, sunlight, day length• Microclimate – shade, air movement, soil type, drainage, trafﬁc• Management – mowing, fertilization, irrigation, cultivation
The Environment Triggers Disease Development• Temperature and water are the most important factors inﬂuencing disease development• Foliar Diseases – low night temperature, leaf wetness duration• Root and Crown Diseases – soil temperature, soil moisture
The Environment Triggers Disease DevelopmentFoliar diseases are triggered by low night temperature • Dollar Spot - >50ºF • Brown Patch – >60ºF • Pythium blight - >65ºF
The Environment Triggers Disease DevelopmentRoot diseases are triggered by soil temperature • Summer Patch - > 65ºF • Take-all Patch - 40ºF to 60ºF • Spring Dead Spot - 60ºF to 80ºF • Large Patch - <70ºF
Why is Accurate Diagnosis Important? • Essential for prompt and effective problem management • Incorrect diagnoses cost TIME and MONEY, and may result in further turf damage • New generation of fungicides and insecticides control a smaller number of diseases or pests
Turfgrass Disease Diagnosis: A process of elimination 1. Start with a list of possibilities based on turf species and time of year 2. Look for clues 3. Rule out diseases, narrow the list of possibilities 4. Repeat steps 2 and 3 5. Send sample to a diagnostic lab
RE MI CE RE CR NT CE OC CU NT LIM LT WE AT Diagnosis Triangle UR AT E, AL HE PR R, AC TIC ES PL DIAGNOSIS AN TA NDSIGNS OF PATHOGEN ST AN D SY PT M OM S
Stand SymptomsSymptoms evident from a distance Spots – less than 4” diameter Patches – irregularly shaped areas greater than 4” diameter Circles – perfectly circular areas greater than 4” diameter Rings – surrounded by healthy turf to the inside and outside Irregular – no pattern
Plant SymptomsSymptoms evident on individual plantsLeaf Spot – round or oval areas on leaves with a distinct borderFoliar Lesions – large, irregular areas on leaves with a distinct borderStem Lesions – large, irregular areas on leaf sheaths with a distinct borderFoliar blight or dieback – necrosis of leaves or entire tillersCrown Rot – necrosis of the crown, rhizomes, or stolonsRoot Rot – necrosis of the roots
Conditions Favoring Disease• Extended periods of hot/humid weather• Most severe when daily low/high is above 70/90 respectively• 10-12 hours continuous leaf wetness• Poor water management• Excessive nitrogen• Perfect recipe ... repeating afternoon thunderstorms after dry spell • Front porch rule
Brown Patch Resistance in Tall Fescue Cultivars 1996 NTEP Trial, Lexington KY KENTUCKY-31 JAGUAR 3 REBEL 2000 WOLFPACK PLANTATION CHAPEL HILL ARID RENEGADE APACHE II MUSTANG IIFALCON III (MB 212) TAR HEEL FALCON II COCHISE IISOUTHERN CHOICE SHORTSTOP II COYOTE BONSAI TOMAHAWK-E CORONADO 0 5 10 15 20 % Brown Patch
Brown Patch Control• All of the labeled fungicides control brown patch effectively• Products differ in “residual control”, or the number of days of control• For tall fescue, application intervals can be extended by 7 to 14 days
Residual Control of Brown PatchQoIs – 21 to 28 daysDicarboxamides – 14 to 21 daysCarboxamides – 14 to 21 daysBenzimidazoles – 10 to 14 daysDMIs – 7 to 10 daysContacts – 7 to 10 daysPolyoxin D – 7 to 10 days
Conditions Favoring Disease• Most devastating ﬁrst year of establishment• Temperatures between 70 and 95 F• 14 hours of continuous leaf wetness• Excessive nitrogen• Heavy rains will promote rapid spread of spores due to splashing effect ... as will mowing
Conditions Favoring Disease• Low temperatures above 65°F• 12-14 or more hours of leaf wetness or high relative humidity• High nitrogen levels• Poor surface or subsurface drainage• High soil pH (above 7.0)
Conditions Favoring Dollar Spot• Low temperatures >50°F• High temperatures <95°F• 10 consecutive hours of leaf wetness• Low nitrogen and other nutrients• Low mowing height• Excessive thatch accumulations
Dollar spot is most severe in under-fertilized turf.