Microscopic identification of turfgrass diseases
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Microscopic Identification of Turfgrass Diseases. Horticulture In-service Training, September 30, 2005 The Inn at Virginia Tech, Blacksburg, VA. Purpose of session. Learn procedure for disease identification Locate and identify fungal structures

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Microscopic Identification of Turfgrass Diseases

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Microscopic Identification of Turfgrass Diseases

Horticulture In-service Training, September 30, 2005

The Inn at Virginia Tech, Blacksburg, VA


Purpose of session

  • Learn procedure for disease identification

    • Locate and identify fungal structures

    • Help confirm/eliminate a field diagnosis based on symptoms

    • Possibly eliminate fungicide applications


Diagnosing turfgrass samples

  • Disadvantage:

    • plants are small

    • many microorganisms in soil

  • Advantage:

    • plants are small

    • verification of initial field diagnosis

    • quicker treatment if necessary


Tell a story with pictures


Useful equipment

  • Dissecting microscope (4 – 40X)

  • Compound microscope (40 – 1000X)

  • Digital camera (Sony, Nikon)

    • Universal adapter

  • Lab supplies

    • Scapula, forceps, probing needle, distilled water or stains, slides & covers, etc.


Dissecting microscope

  • Useful for observing mites, insects, and some fungal structures

  • Helps pinpoint problematic areas

  • Not powerful enough for fungal ID


Compound microscope

  • Difficult to pinpoint if starting blind

  • Useful for distinguishing fungal hyphae, spores, fruiting bodies, and other structures


Digital camera

  • Can be mounted on microscope

  • Provides documentation for archives

  • Rapid sharing of information

  • Tell a story


Factors affecting disease diagnosis

  • Turf species and cultivar

  • Weather patterns, time of year

  • Cultural and chemical inputs

  • Symptoms and signs


Diagnostic procedure

  • Collect information

  • Examine plant under dissecting scope

  • Identify problematic regions

  • Make wet mount from diseased tissue

  • Examine under compound scope


Diagnostic procedureCompound microscope

  • 4x- focus and find fungal structures

  • 10x- to pinpoint spores, hyphae, etc.

  • 40x- identify fungus based on spore and hyphae characteristics


What to look for

  • Spores

  • Hyphae

  • Fruiting bodies

  • Plant parasitic nematodes


Hyphal characteristics

  • Septation

  • Branching

  • Pigmentation

  • Consistency


Spore morphology

  • Shape

  • Number of cells

  • Spore origin


Moist Chamber

  • Promotes disease development, mycelial growth, sporulation

  • Sample placed in plastic container with moist paper towel & checked daily


Rhizoctonia species on turf

  • Rhizoctonia solani

    • Rhizoctonia blight

    • “warm weather” brown patch

  • Rhizoctonia cerealis

    • Yellow patch

    • “cool season” brown patch

  • Rhizoctonia zeae

    • Rhizoctonia leaf and sheath spot

    • “hot weather” brown patch


Rhizoctonia characteristics

  • Right angle branching

  • Septate (cross walls)

  • Uniform hyphae

  • Septae near branching

  • Constricted hyphae at branching point


Pythium species

  • Pythium blight

  • Pythium root rot


Pythium characteristics

  • Coenocytic (no cross walls)

  • Small, thin filamentous hyphae

  • Oospores

  • Sporangia

  • Non-pigmented

250x

540x


Dollar spotSclerotinia homoeocarpa

  • Clear hyphae

  • Variation in size

  • Often branches in V

  • Granular cytoplasm


Gray Leaf SpotPyricularia grisea (oryzae)

  • Spores (conidia) are hyaline

  • Pyriform shaped

    • Bowling pins, pear, ice cream cone

  • 2- to 3-celled conidia borne on slender stalks (conidiophores)


AnthracnoseColletotrichum graminicola

  • Acervulii w/ setae on leaf and crown tissue

U. Of Guelph


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