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Scouting for turf diseases

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The following key is patterned after Shurtleff (1987) in “Controlling Turfgrass Pests” but has been adapted to turfgrass diseases common in Massachusetts. The four sections include COLD, COOL/WARM, and HOT temperature diseases as well as problems not generally related to temperature.

Technical terminology has been minimized. The word “mycelium” (or hyphae) refers to the web-like growth of fungi on turf when wet. “Black specks” are the spore containers produced by a few of the disease causing fungi. “Sclerotia” are dark, pinhead-sized or slightly larger masses of mycelium that some fungi produce as survival structures.

How to use this key

Decide first the temperature when symptoms first appeared. Then read the subsections to decide which best describes the problem. Symptoms of diseases are often quite different on lawns than on highly maintained, low-mown turf such as putting greens. The most common diseases are indicated by a star (★).The diagnosis of turf diseases can be difficult even in the laboratory. Use this key only as a general guide. For information about disease diagnostic services available from UMass, refer to the UMass Extension Plant Diagnostic Lab at ag.umass.edu/services/plant-diagnostics-laboratory.

Section I. Cold Weather (32–45°F) Diseases and Disorders

A. Irregular patterns or streaks in turf.

  1. Bleached or dead grass, especially in wind-swept areas free of snow with deeply frozen soil. WINTER DESICCATION
  2. New leaves killed back, often in yellow to white patches following freezing temperatures. SPRING FROST

B. Turf killed (rotted or straw-colored) in wettest areas.

  1. May follow drainage patterns. WATER AND ICE DAMAGE
  2. Distinct circular patches of dead grass from 1” to 3” across.
    1. Wet grass is often covered with white to bright pink mycelium; NO sclerotia present. « MICRODOCHIUM PATCH (PINK SNOW MOLD)
    2. Wet grass covered with white to gray or bluish-gray lint-like mycelium; small yellow to dark brown or reddish sclerotia often present in or on grass leaves. « TYPHULA BLIGHT (GRAY OR SPECKLED SNOW MOLD)

Section II. Cool-to-Warm Weather (45–75°F) Diseases

A. Circular patches or rings in turf after grass greens up in spring.

  1. Yellow patches or “tufts” usually less than 1” across. Plants easily pulled from turf. DOWNY MILDEW (YELLOW TUFT)
  2. Sunken, straw-colored patches, 1” to 6” across. May be covered with dense white mycelium in moist weather.
    1. Whitish tan leaf spots with brown, reddish brown or purplish borders. ★ DOLLAR SPOT
    2. Turf wilted, killed, rotted or straw-colored. Often in poorly drained areas. PYTHIUM ROOT ROT
    3. Leaves yellowing and wilting; tiny black, spiny fungal hairs in tufts may be evident with a hand lens. ★ ANTHRACNOSE (CROWN/BASAL ROT)
  3. Patches from 1” to 3’ across.
    1. A prolonged cool rain commonly following melting snow. Wet grass is often covered with white to bright pink mycelium or may be greasy to coppery in color. ★ MICRODOCHIUM PATCH (PINK SNOW MOLD)
    2. Patches usually with green centers.
      1. Yellow to straw colored, sunken in high cut turf. Wet grass not covered with mycelium. ★ YELLOW PATCH (COOL WEATHER BROWN PATCH)
      2. Initially yellow, then reddish brown or bronzed, and finally sunken, tan rings. Centers often invaded by weeds. Most commonly found in cool, moist, coastal areas; most common in bentgrass. « TAKE-ALL PATCH
      3. Patches, rings, arcs, “frog-eyes” about 6” to 8” across, enlarging later. Most common in Kentucky bluegrass sod two to four years old and annual bluegrass. ★ NECROTIC RING SPOT
  4. Rings or arcs up to 15’ or more across; often with outer ring of dark green grass; may be mushrooms in rings; often dead turf on highly managed areas in golf course. ★ FAIRY RING

B. Irregular patterns (usually) in turf.

  1. Colored fungus or spores on leaf surfaces; leaf spots not usually evident.
    1. White to gray powdery mycelium and spores on leaf surfaces; found mostly in shade. ★ POWDERY MILDEW
    2. Gray to black streaks of black powdery spores in leaves; leaves shred into ribbons and curl. Grass may later die in irregular patches or a general thinning; usually in turf three or more years old. LEAF SMUTS
    3. Pink to reddish and mycelium flecks on leaves; red thread-like growths beyond leaf tips; appears tan in patches; most common in low nitrogen turf. ★ RED THREAD/PINK PATCH
    4. Bright yellow, orange, or reddish-brown pustules of powdery spores on leaf blades; mostly late summer, usually on slow growing and low fertility turf. ★ RUSTS
    5. Slimy, superficial whitish gray to yellow fungus-like material in the early stages; turns powdery later. SLIME MOLDS
  2. Irregular patches of turf lacking distinct fungal signs.
    1. Increased leaf senescing on annual bluegrass (indicated by tan patches) or purpling of bentgrass on putting green height turf. Turf may also be off-color, thin or slow-growing in variably-sized patches. PYTHIUM ROOT DYSFUNCTION
  3. Leaves distinctly spotted or with tip blight.
    1. Oval to eye-shaped, dark-bordered spots. In warm weather, turf may look thin and weak (melting-out). ★ LEAF SPOTS AND BLIGHTS/MELTING OUT

Section III. Hot Weather (over 75°F) Diseases

Occur from late spring to late summer.
Possibilities from previous sections

Circular patterns in turf:

  • Dollar Spot
  • Necrotic Ring Spot

Irregular Areas:

  • Rusts
  • Slime Molds

A. Circular patterns in turf.

  1. Straw colored patches often 6” to 8” across, but can be larger; centers often remain green. Most common on Kentucky bluegrass sod two to four years old and in annual bluegrass. Symptoms often appear in hot weather after heavy rains. Symptoms identical to necrotic ring spot.  SUMMER PATCH
  2. Patches up to 2’ to 3’ across; light brown; grass blades usually not matted. Patches appear during wet periods. Gray mycelium may be visible in moist conditions; most common on bentgrass greens (look for “smoke ring”) and tall fescue lawns (distinct tan or chocolate brown lesions on leaf blades).  BROWN PATCH
  3. Tan leaf spots without darker borders. Grass leaves matted and slimy. Copious amounts of dense gray/white mycelium in moist weather.  PYTHIUM BLIGHT
  4. Yellow/golden brown rings (3” to 12” in diameter) on annual bluegrass putting greens. Rare on creeping bentgrass. Rings may have scalloped appearance and enlarge over time. BROWN RING PATCH (WAITEA PATCH)
  5. Circular patches (1” to 2” diameter). Tan dead tissues with reddish-brown borders on young, sand-based bentgrass putting greens. BENTGRASS DEAD SPOT
  6. Circular copper or salmon colored patches less than 3” in diameter, during humid weather. Most common on golf course putting greens. COPPER SPOT

B. Irregular patterns of weak, thin, dormant or dead grass. Large areas appear dry, then wilt, and turn brown.

  1. Turf is yellowish, then reddish brown. Leaves spotted to blighted. Tiny black, spiny fungal hairs in tufts on blades evident with hand lens. Most common in compacted, stressed turf. Most common on annual bluegrass golf course putting greens.  ANTHRACNOSE (CROWN/BASAL ROT)
  2. Oval or eye-shaped leaf spots with dark margins, mostly on Kentucky bluegrass. « LEAF SPOTS/BLIGHTS/MELTING OUT
  3. Irregular gray to brown leaf spots with dark margins and yellow halo. Mostly on perennial ryegrass and tall fescue. GRAY LEAF SPOT
  4. Recently seeded areas have irregular, empty areas due to poor germination. Dying and dead seedlings have dark or black coloration. DAMPING-OFF, SEED ROT
  5. Irregularly thinning turf, soil surface with has green or black coating that is slimy to the touch. ALGAE
  6. Irregularly thinning turf, soil surface has a thick, silvery green mat. MOSSES

Section IV. Other Causes of Poor Turf Usually Independent of Temperature.

A. Turf gradually becomes pale green to golden yellow and grows slowly; stand often thins out.

  1. Definite leaf lesions or mottling present. AIR or SOIL POLLUTION
  2. Yellow streaks may form parallel to the leaf veins. IRON or NITROGEN DEFICIENCY

B. Turf suddenly appears scorched.

  1. Usually in patches, bands or streaks. CHEMICAL BURN or MOWER BURN
  2. Bands, streaks, or irregular patterns; grass is stimulated at margins. FERTILIZER BURN
  3. Ring of dark green grass at margins; patches up to about 1’ across. DOG INJURY
  4. Entire turf area or patches over slight elevations or mowing corners are yellow to brown. SCALPING INJURY
  5. Leaf tips are shredded; appear gray, then tan. DULL MOWER INJURY

C. Round to irregular patches of dead or dormant grass; often follows dry periods. BURIED DEBRIS, INSECT INJURY or THICK THATCH

D. Turf bare or thinned; often in traffic areas, dense shade, waterlogged soil, etc.

  1. Greenish to brown scum that later forms a black crust. ALGAE
  2. Small green plants that grow on soil in slight mounds. MOSS
  3. Soil hard in heavily tracked paths, under swings, etc. COMPACTION

E. Turf dry, bluish green (footprints visible), wilts may later turn brown. DROUGHT, WILT or IMPROPER WATERING