Common name

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Cogongrass Biology and Impacts
Greg MacDonald University of Florida
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Introduction

• Native to southeast Asia
• Infests nearly 500 million acres worldwide
• Found on every continent
• Except Antarctica
• Tropical and subtropical areas, limited spread to
  northern temperate regions
• Considered to be one of the worst weeds

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Introduction to U.S.

• First appearance
• Grand Bay, Alabama
• Escape from crate packing in 1912
• Intentional introduction
• Mississippi as a possible forage in 1921
• Florida introduction 1930s and 1940s
• However, little economic (forage) benefit

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Cogongrass infestation in the southeastern
United States
points of introduction
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Adaptation

• Highly adapted to poor soils
• Ability to survive low nitrogen, phosophorus
• Prefers low pH soils with low organic matter
• Extremely drought tolerant through specialized
  rhizome features
• Unique photosynthetic mechanism
• C4 photosynthesis
• Adapted to low light environments (lt5 sun)

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Pyrogenic

• Fire-based species
• Accumulates excess leaves for fire
• Burns hotter (15-20 C) than normal understory
  fires
• Eliminates trees, shrubs, other forbs maintains
  dominance

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Cogongrass Biology

• Grows in loose to compact bunches, containing
  several leaves
• Leaves arise from a central area along a rhizome
• Originate directly from ground level

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Leaves

• 1-4 feet in length, ½ to ¾ inch wide
• Prominent, off-center, white mid-rib
• Margins are finely serrated, accumulate silicates

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Seed Production

• Predominately in the spring
• Long, fluffy-white seedheads
• Mowing, burning or fertilization may induce
  seedhead formation

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Seeds

• Extremely small
• Attached to a plume of long hairs
• May be carried long distances by wind or humans
• Over 3000 produced per plant
• Relatively short lived, lt 1 year

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Rhizomes

• Comprise over 60 of total biomass
• 40 tons per acre
• Penetrate soil to a depth of 4 feet, but most
  found in the top 6 to 10 inches

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Rhizomes

• Rapid regenerative capacity
• Central core to resist breakage and drought
  tolerance
• Scale leaves surround each bud

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Rhizomes

• Multiple buds per rhizome section
• Apical dominance maintains dormancy
• Evidence of additional dormancy mechanisms

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Allelopathy

• Rhizomes exude substances that retard the growth
  of other plants
• Increasing cogongrass density excludes other
  vegetation

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Varieties of Cogongrass?

• Var. major
• Var. europa
• Var. africana
• Var. condensata
• Var. latifolia
• Imperata brasiliensis Brazilian satintail

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var. Rubra

• Red variety of cogongrass
• Sold widely in the ornamental trade
• Red Baron, Japanese Blood Grass

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Rubra

• Will revert to the normal green biotype
• Conflicting reports on aggressiveness
• Appears to be cold-tolerant
• Genetically related to I. brasiliensis??

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