The Environment of Turfgrass Pathogens

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The Environment of Turfgrass Pathogens
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HOST PLANT
DISEASE
PATHOGEN
ENVIRONMENT
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Pathogen Life History
infection
dispersal
2O cycles
colonization
survival
reproduction
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Pathogen Life History
infection
dispersal
2O cycles
colonization
survival
reproduction
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GRASS
GRASS PATHOGENS
ENVIRONMENT
LOW DISEASE POTENTIAL
HIGH DISEASE POTENTIAL
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GRASS
GRASS PATHOGENS
ENVIRONMENT
LOW DISEASE POTENTIAL
HIGH DISEASE POTENTIAL
SEASON WEATHER LANDSCAPE
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LANDSCAPE EFFECTS
Highly exposed
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LANDSCAPE EFFECTS
Low air movement
Shading
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In natural ecosystems, disease is common, but
epidemics are rare
Disease across a population epidemic
Disease on individual plant
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Turfgrass is prone to epidemics

• Monoculture
• High plant density

Leaf to leaf hyphal growth
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CANOPY
Two parts of the environment
ROOT ZONE
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Above-ground environment for pathogens Positive
factors
Nutrients Sugars and amino acids from plant
(wounds), air (pollen), insects (honeydew)
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Above-ground environment for pathogens Positive
factors
Moisture Atmospheric (humidity) Supports fungal
growth (gt95RH) Prevents dessication Free
moisture (leaf wetness) Needed for spore
germination Bacterial growth and
mobility Nutrient transport Sources dew,
guttation, rain
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Dew
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Guttation
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Above-ground environment for pathogens Negative
factors
Ultraviolet light

• Lethal and mutagenic

• Air movement (wind)
• Causes drying of leaf surface
• Some beneficial effects for
• pathogen, however
• - Evaporative cooling
• - Pathogen dispersal

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Effects of some cultural practices on canopy
environment
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Mowing provides wounds Source of nutrients Point
of pathogen penetration
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Irrigation Lengthens leaf wetness
period Increases canopy humidity Cools leaf
surface
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By design, turf grass is planted in
high densities. This results in - Reduced
ultraviolet penetration - Reduced leaf
temperatures - Reduced air movement through
canopy - Increased canopy humidity - Increased
leaf wetness period
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Below-ground environment for pathogens

• Pathogens typically located within top 8 inches
  of soil profile
• Most are stationary
• Nutrients and host plant must come to pathogen
• Pathogens remain dormant unless provided with
  nutrients

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3
Two parts of the environment
CANOPY
THATCH
ROOT ZONE
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3
Two parts of the environment
CANOPY
Little to no UV Leaf wetness nearly
continuous Very high humidity
THATCH
ROOT ZONE
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3
Two parts of the environment
CANOPY
psuedo-root zone
THATCH
Growth and infection by root pathogens!
ROOT ZONE
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Summary

• Disease epidemics are uncommon in natural stands
  of grass
• Cultural practices cause turf grass to be prone
  to epidemics
• Cultural practices modify the environment to be
  more consistently favorable to pathogen growth
  and infection